Australia's First 4 Billion Years: Awakening

PBS Airdate: April 10, 2013

RICHARD SMITH (Biologist): Over four billion years in the making, an island adrift in southern seas: it's Australia, the giant down under; a young nation with all the gifts of the modern age, but move beyond the cities and an ancient land awaits, one nearly as old as the earth itself.

Australia is a puzzle, put together in prehistoric times. And the clues that unlock the mystery can be found scattered across Australia's sunburnt face.

I'm Richard Smith, and this is an amazing country. I'll show you that every rock has a history, every creature a tale of survival against the odds. Join me on an epic journey across a mighty continent and far back in time.

Of all continents on Earth, none preserve the great saga of our planet and the evolution of life quite like this one. Nowhere else can you so simply jump in a car and travel back to the dawn of time.

In this episode, the beginning of it all: from a cosmic maelstrom a planet is born. This is no paradise, but, somehow, life gains a toehold then is nearly frozen out.

This is the tale of the first Australians, how they survived and flourished. From Australia's ancient stones comes the story of our world. Australia's First 4 Billion Years: Awakening, right now, on NOVA.

The best way to understand the story of Australia is to get out into it, feel the sun beating down on its ancient bones. And I do mean "ancient." To get a true appreciation of how old Australia really is, you need to get a sense of Deep Time.

Okay, so this looks like a pretty ordinary four-wheel drive, but imagine, just for a moment, that it's fitted with a Deep Time Drive. I simply dial up the time I want to go to and, by the magic of time-shifted G.P.S., it does the rest.

G.P.S. VOICE: You have selected the Beginning.

RICHARD SMITH: I've set the controls for a million years per minute. That's 60-million years of history for every hour we travel down the road. You want to see the real old Australia? It's quite a ride.

At a million years per minute, a blink of an eye sees us in an Australia before Europeans. A few seconds later and we pass the first Aboriginal footprints. Within minutes, you're dodging marsupials the size of minivans and dragons far longer.

G.P.S. VOICE: Caution: hazardous wildlife.

RICHARD SMITH: Worried about roadkill? It gets worse. An hour down the road and suddenly the land is dominated by dinosaurs.

It will stay this way for the next three hours, as we barrel back, deep into the past.

G.P.S. VOICE: Recalculating Deep Time.

RICHARD SMITH: Over 250-million years down the road of time—about four hours at this speed—and it's the world before dinosaurs; even further, and there is no life on land at all. I drive on. At 500-million years—about eight hours since we left the present day—all life is underwater and distinctly weird. But time is deep; there's still 90 percent of history to go.

While the entire history of humanity occupied only the first few seconds of this journey, and complex animals the first nine hours, I have to travel back over two and a half days, at this speed, to reveal the first stirrings of life.

G.P.S. VOICE: Caution: destination approaching.

RICHARD SMITH: Finally, after over three days travelling at 60-million years an hour, I've driven back four-and-a-half-billion years. I've run out of road. We have arrived in the darkness at the edge of time.

When the first rays of the newborn sun shone out into space, they illuminated a scene of untold cosmic violence. Swirling around the young star, was a disk of dust and debris, every fragment locked in mortal gravitational combat with every other lump of rock, metal, ice and dust in orbit. This is the process of gravitational cannibalism that marked the formation of all the planets. And the earth grew bigger and hotter with each conquest. The heat came not only from collision, but from the natural radioactivity building up inside.

Then, just as the outer crust was beginning to harden, it's thought our planet was almost wiped out. Another competitor, this one the size of Mars, crossed Earth's path.

The aftermath was the formation of our pale, airless companion: the moon, and the red-hot, iron-rich ball of rock we know today as home.

Understanding the fiery birth of the earth really helps explain how the engine of our planet works. The crust I am sitting on might have cooled down, but the planet below all of us is still a hot ball of rock, spinning around in cold space. And it's still trying to cool down.

And as long as it cools, the continents we sit on continue to move. This is the engine of plate tectonics that's driven the story of our world since day one. And for Australia, we can pretty much date that first day.

Nearly 2,000-billion sunrises after that first dawn, I'm heading west, to one corner of the country that has faithfully kept a record of the earliest days of Planet Earth.

SIMON WILDE (Curtin University of Technology): So, we are almost there. Just in, just in front of us there,….

RICHARD SMITH: For decades, geologist Simon Wilde has been climbing the Jack Hills in Western Australia, date-stamping the early earth.

SIMON WILDE: This is the famous discovery outcrop, the site where the world's oldest zircon crystals have been recorded.

RICHARD SMITH: Though ancient, it's not the rocks themselves that are so old here, but the microscopic crystals of zircon within them. Known in the gem trade as poor man's diamonds, zircon crystals form when molten rock cools in the earth's crust. And, just like diamonds, zircons are forever.

If you ever wanted to find a spot to ponder your oneness with the great age of the earth, you couldn't do better than this rock, because, within it, are the oldest remnants from the early earth ever found: older than you and I by a mere 4.4-billion years.

At just a whisker younger than the age of the planet itself, this tiny treasure, zircon W74, is the ultimate Aussie survivor.

Recycled from rock to rock, zircons like W74 have resisted everything the planet has thrown at them. And yet, they've somehow managed to keep a diary of the earliest days locked deep within their crystal lattice.

Reading that diary in the lab has been a revelation.

The oldest zircons, it seems, crystallized inside molten continental granite that cooled rapidly in the presence of abundant liquid water. Waves were probably breaking against the cooling shore of the future Western Australia, within a-hundred-and-fifty-million years of the earth's formation.

Today's sun beats down here on tiny fragments of what may be our planet's oldest continent and much of the earth's most ancient rock. It's no surprise then that Australia feels like an old, tough country.

Within a stone's throw of the Jack Hills is the nearby Mileura Station. Here, third-generation rancher Patrick Walsh ekes out a living from the oldest corner of an ancient land, a red and rocky heritage from the dawn of time.

The geologists are up there getting terribly excited, bashing rocks.

PATRICK WALSH (Mileura Station): Oh, yeah, they're very excited. I always joke with them and say that that's the new G spot in geology, because, you get a good laugh out of it, and I, you know it is important; it did rewrite the, the geology books. That doesn't happen every day.

RICHARD SMITH: This new picture of the young Earth is of a landscape you might have recognized: rich in water, clouds and raw geology, but almost totally devoid of oxygen.

If you were lucky enough to have been able to travel back to the very earliest days of the planet, you would have been treated to some of the greatest shows on Earth. But you would have needed a lot more than a hard hat and a gas mask, because this was a very dangerous world.

We can tell, from the heavy cratering on the moon at this time, that the early earth must have been pounded to within an inch of its life.

You can get a sense of what this must have been like by visiting Wolfe Creek Crater in the Kimberly.

The great thing about Wolfe Creek Crater is, because it's so fresh, relatively speaking, it's a terrific place to see what sort of impact a big impact can make.

When the object hit over there, it released so much energy that it set off an explosion the equivalent of an almighty nuclear blast. As the material came out, it literally flipped the rock back onto itself around the edges. This sandstone is now leaning back, and everything that was in there either vaporized or was hurled out into the surrounding countryside.

But Wolfe Creek crater was formed only recently, by an object probably only a few yards across.

Combine at least one 30-mile-wide asteroid striking the earth every century with a corrosive acidic atmosphere and you probably have the reason why so little of the early earth survives.

The craters of the moon show that the great bombardment slowed about 3.8-billion years ago. But while the moon's face has changed little, the Archean earth looked nothing like the world today: none of our familiar continents, no green blush of life on land.

But dive into those ancient Australian seas and you would have found the first stirrings of life. It probably looked like this: slime. Some of the earliest tantalizing signs of what could be fossilized bacteria appear in Western Australian rocks about 3.5-billion years ago, not long after the meteor bombardment ended.

While the details of the origin of life remain shrouded by the mists of time, scientists are starting to get a fix on when, and probably where, it happened. And one thing is for sure, the early earth had plenty of the raw ingredients: a reliable supply of water, heat and biologically useful chemicals could all be found close to volcanic vents, like in these hydrothermal pools, in New Zealand. This blistering water contains no free oxygen; instead, it's rich in poisons, like hydrogen sulfide and arsenic, and rich in life, too. The orange scum lining the rocks is a jungle of primitive bacteria and archaic microorganisms, all feeding on the noxious goodies oozing from the hot earth below.

Similar environments have existed in the sunless deep sea for billions of years. Both habitats are home to the most primitive life forms we know, and both are closely linked to the dynamic tectonic world we now live on.

Wherever it started, life soon took hold in the sunlit shallows, and to see what it looked like, we need to head to the beach.

The Australian outback: bone dry and baking hot, hardly the sort of conditions you'd associate with the origin of life. But it's precisely because of this tough environment that down at the end of this road we can find a unique glimpse into the world of the dawn of life.

If you ever wanted to pay a visit to your most distant ancestors, then Shark Bay, in Western Australia, is the place to do it.

The high rates of evaporation here, in Hamelin Pool, make this shallow water twice as salty as the open sea, just the sort of tough preserving conditions for slow-growing old-timers who prefer to be left alone.

Meet your most distant living relative: the stromatolite, still going strong here in the salty waters of Shark Bay. Now, these guys might look more like rocks than your relatives, but you shouldn't be easily fooled. On the outside is a vast living community of microscopic bacteria that have developed the knack of gluing mud into mounds. And they've achieved this with the revolutionary trick of harnessing the power of sunlight.

Photosynthesis changed the world. No longer slaves to volcanic energy, light-harvesting bacteria began to spread to any sunlit surface in the sea. And growing as stromatolites, they could even make their own. It's the ultimate living rock.

How the bacterial colonization of those distant shores began is a puzzle that scientist David Flannery is keen to solve, and a simple living algal mat offers a remarkable clue.

DAVID FLANNERY (University of New South Wales): It's much easier to interpret things in the fossil record if you have a modern example. Here is a piece of rock from Western Australia in the Pilbara that's 2.7-billion years old, and it has a very similar structures, and it comes from a very similar environment. You can see the modern example is made up of these tufts and ridges and this polygonal pattern, and the fossil example is made up of the exact same stuff.

RICHARD SMITH: They may come in a range of shapes and sizes, but these high-rise bacterial communities have barely changed in billions of years.

To swim here is to take a dip deep into the past. This is a time tourist's trip to a three-billion-year-old beach.

We know that stromatolites dominated the ancient Australian shorelines, because you can still visit them, preserved in the rocks of Western Australia's Pilbara region.

The town of Marble Bar—population about 350, plus a few dogs—claims the dubious distinction of being the hottest town in Australia. It's probably why some joker dubbed this torrid little spot, a few hours out of town, "North Pole..

Geologists can read perhaps the oldest preserved planetary landscape in the rocks here, a coastline with beaches and sandbars and something else: the gentle laminations in these rocks have been interpreted as the first tangible evidence of life.

Visible to the naked eye, these may be the world's oldest fossilized stromatolites, dated to nearly three-and-a-half-billion years. Though the biological origin of the oldest fossils is still debated, the Pilbara's rocky ranges are clearly awash with once-living stromatolites that, in places, must have formed extensive coastal reefs.

As far as we can tell, this was the Australian seaside, circa 3,000-million years ago: stromatolites in the shallows, smoke on the horizon and fire in the sky.

These simple life forms made their mark on the world in a far bigger way than as fossils in the landscape. They started making the landscape themselves. South of "North Pole," lies another Pilbara treasure, Karijini National Park.

I'm taking a shortcut to the distant past. The deeper I drop into iron-rich Hancock Gorge, the further back in time I travel.

Down here, you can look back at one of the earth's great turning points. Two-and-a-half-billion years ago, the atmosphere was still without oxygen, but beneath the waves, stromatolites and their photosynthetic kin were steadily releasing this reactive waste product into the water.

It didn't get far. The oceans were full of dissolved iron left over from the planet's formation. Mix oxygen with iron and you can guess the result. The oceans began to rust.

Year after year, for hundreds of millions of years, the oceans rusted. Layer by layer of rich, red ooze settled softly onto the deep sea floor.

Now, this is what I wanted to show you. See these dark bands of iron? This is the so-called "banded iron" formation. Now, each one of these layers represents a rain of rust that fell to the sea floor, two-and-a-half-billion years ago. And you can see these pale bands in between. Now, nobody knows if this represents some kind of strange seasonality, but if you think that every one of these layers of rust represents a pulse of oxygen in the oceans, then what you are looking at is the planet breathing: the first breaths of the biosphere.

Today, that first biosphere breathes life into the Australian economy. The massive iron ore deposits of the Pilbara are the direct economic legacy of the rusting of the oceans.

It's not until you stand deep in the pit of an iron ore mine, like Mount Whaleback, that you get the true sense of the scale of the rusting of the oceans. The hills here are literally made of iron. Every year, over 33-million tons of ore are mined at Mount Whaleback alone. And this is the business: high-grade iron ore, exposed to sunlight for the first time in billions of years. Bang it together, it sounds like metal. And this stuff is heavy.

All of this, Australia's great wealth of iron, because of a waste product pumped out by microscopic bacterial slime, operating on an industrial scale in those ancient seas.

The empire of the stromatolites was, without doubt, the greatest in the history of the earth. Forget the Romans, the Persians, even the dinosaurs. These humble bacterial mounds dominated the planet for over 2,000-million years, and they engineered its greatest transformation.

Once turned on, the oxygen tap could not be turned off. The formation of iron was just a phase the earth was going through. After 700-million years of rusting, the oceans pretty much ran out of iron, and the oxygen had nowhere else to go but up.

Now, for the first time, oxygen began flooding into the atmosphere. It was to be the greatest pollution event in history. Without the oxygenation of the atmosphere, we wouldn't be here, nor would the myriad species we share the planet with.

There might have been a revolution underway, but there wasn't much for a time tourist to see or breathe, for that matter. With oxygen concentrations at only a twentieth of today's levels, your first gasp would have been your last. Even geologists have found the second half of the Proterozoic a little, well, a little dull. After all the earlier dramas, things got stuck in such a long geological rut that they've dubbed this period "the boring billion..

But it was quite a good time for continental construction. The hot planet below had been busy pushing and welding together the ancient chunks of continental landmass that, today, make up most of the western two-thirds of Australia.

By about a billion years ago, most of the wandering continents, including embryonic Australia, had been crunched together into a super continent called Rodinia. Fossil evidence points to some of the first seaweeds, sponges and embryos appearing at this time. Life was moving beyond bacteria, and just as it did so, it was nearly stopped in its tracks.

Welcome to "Snowball Earth..

Unmistakable evidence from around the world points to two great waves of glaciation that locked the planet in the firm, icy grip that gave the Cryogenian its name. These were the most severe ice ages in the planet's history.

The Flinders Ranges, in South Australia, seem a world away from a great global ice crisis, yet it was here that clues to just such a calamity were first found. Paleontologist Jim Gehling sees hard evidence for cold climates in these old sea floor muds.

JIM GEHLING (South Australian Museum): This is tidal, rhythmic sedimentation. In other words, every single tide has been recorded as a couplet of layers. The beauty of this, it's a complete record of tides for as much as 60 years, and that is unique for rocks that are 640-million years old.

RICHARD SMITH: These soft sediments settled on the sea floor with the precision of grooves, on an L.P. record, each band turning to the beat of an ancient tide. The fine undisturbed layering of this tidal calendar could only have formed one way: with the sea floor protected by a ceiling of ice.

JIM GEHLING: The sea floor was actually sealed off from waves and storms, because there was an ice cover over it. We were almost straddling the equator, and yet, this ocean was covered with ice.

RICHARD SMITH: This is what we think the oceans of our planet would have looked like during one of these events: frozen solid from the poles to the tropics. Now, this is the frozen Arctic Ocean, north of Barrow, in Alaska, today. In a month or two, most of this ice behind me will break up and drift away. It'll come back next year, but just imagine if the ice set in, not for a season, not for a century, but for a million years or even 10-million years. It's very hard to imagine anything surviving such a cold, cold world.

But survive it did. It was plate tectonics to the rescue! Furious volcanic eruptions, it's thought, primed the atmosphere with greenhouse gases, and the "Great Snowball" was soon followed by the "Great Thaw..

As the icecaps melted, seas rose and flooded back across the land, but the world that returned had changed. Life had not only survived the icebound snowball years, it was about to flourish.

The moment is caught in time, here, in the Flinders Ranges, with a sudden shift to warm yellow rock, the so-called "golden spike..

Now, "So what?" you might ask. Well, this is a really significant moment in Earth history, because everything down here is icehouse, the end of the great snowball earth; but up here, the planet's returned to greenhouse conditions. But much more than that, at this precise point, 634-million years ago, we suddenly enter a world clearly inhabited by animals.

In a secret location, in the hills, not far away, Jim Gehling and his team have unearthed a whole section of sea floor, a tableau of life in the Ediacaran. These are some of the oldest multicellular animals to be found on Earth, so significant that their discovery near Ediacara, in the Flinders Ranges, has given the age its name.

JIM GEHLING: So you're looking at a snapshot of life, on the quiet bottom, just below the reach of waves during fair weather.

RICHARD SMITH: Here was a garden of strange animals: frond-shaped creatures feeding in the current, others resembling anchors and throat lozenges.

JIM GEHLING: Now, the most common one is this little pancake-shaped thing, Dickinsonia.

RICHARD SMITH: Like a puffed up placemat, Dickinsonia could reach about three feet across. It seems to have slid slowly over the sea floor, stopping from place to place to feast on the carpet of bacterial slime. One of the puzzles has always been, though, how did these creatures feed.

JIM GEHLING: It probably crawled over the mats, decayed the mat underneath it and absorbed the nutrients.

RICHARD SMITH: So, no mouth.

JIM GEHLING: No mouth.

RICHARD SMITH: What is certain is that there were things moving about on the sea floor looking for food.

What's this guy here.

JIM GEHLING: Oh, yeah, now that's one of my favorites. It's spriggina, and it's important, because we see that there's a head end, looks like a shield,….

RICHARD SMITH: Yes.

JIM GEHLING: …;with a bulge behind that,….

RICHARD SMITH: Yes.

JIM GEHLING: …;which might just be a concentration of its sensory organs.

RICHARD SMITH: So a brain? An early brain.

JIM GEHLING: That's right, so the first smart creature on Earth, perhaps.

RICHARD SMITH: Maybe the last.

Spriggina was an animal on the prowl, a pioneer crawling into the record books, right here on a long-lost Australian shoreline.

JIM GEHLING: The record that we have here is of the first animals, the Ediacara biota, which could actually move and feed on the sea floor. And forever after, the earth was going to change.

RICHARD SMITH: For the great bulk of the planet's history, we've travelled through a landscape where raw geology ruled the world, and slime ruled the waves, and now, after nearly four-billion years on the road, we've arrived at the end of the beginning.

While life was starting to soften the planet's surface, Earth's underground heat engine had been busy driving Australia, Antarctica, India, Africa and Madagascar together into the famous supercontinent, Gondwana.

As the Gondwanan giant was shunted together, shockwaves rippled across the Australian mainland, pushing up a titanic mountain range, the Petermanns, that once towered over central Australia. By the time the sun was glinting off their jagged icy peaks, it was also sparkling through into the first seas of the Cambrian.

TICKET AGENT: There you go.

RICHARD SMITH: Thank you, very much.

A time-travelling tourist to Australia, 540-million years ago, would have been able to complete what is today an impossible journey.

FERRY WORKER: Push it right over that side, mate.

RICHARD SMITH: Thanks, mate.

You would have been able to board a ship somewhere to the north of Cairns and sail inland, almost to the south of Adelaide. The eastern states of Australia, where they existed at all, were still mud at the bottom of the tropical sea.

If you'd been able to gaze down into those warm ancient seas, you would have seen that they were teeming with an abundance and diversity of life, the like of which the planet had never seen.

It's been dubbed the "Cambrian Explosion," a reflection of just how quickly animals took over the oceans at the time. There'd been strange creatures in Australian seas ever since the Ediacaran, but now, suddenly, things that might not look out of place on a seafood platter were scurrying over the sand.

One of the best places on the planet to meet them is Kangaroo Island.

Tucked away, high above the waves of Emu Bay, lies one of the world's premier Cambrian fossil sites.

This is awfully good fun, but I have to keep on reminding myself that what I'm actually doing here is taking a half-billion-year-old rock, tapping it with a hammer, and coming face to face with perfectly formed little crustacean-like things that were scurrying around over 500-million years ago.

These are trilobites, ancestral arthropods that made their grand entrance in Cambrian seas.

JOHN PATERSON (University of New England, Australia): The Cambrian Explosion was a time period in the history of life which is probably one of the most significant in our earth's history. We see animal groups that are recognizable today first appearing in the fossil records, so, the arthropods, for example, things like spiders and crustaceans and insects. And the mollusks are another major group that we see today. They have their recognizable beginnings in the Cambrian.

RICHARD SMITH: There are so many trilobites found at Emu Bay, they must have been scuttling everywhere. The gentle days of the garden of Ediacara were over. This was a world of mouth parts and mobility, hunters and the hunted. Armor-plated arthropods patrolled the seas, searching for easy pickings, they were bug-eyed and bristling with new technology.

Astonishingly, some of their soft body parts have been exquisitely preserved. Here's looking at one of the world's oldest eyeballs.

Here's a decent-sized beastie, a trilobite called Redlichia. Now, you can see all its segments quite clearly and you can see this beautiful head shield with these big spikes down each side.

But if you look even more closely, up here, you'll see its two antennae…;just amazing.

Growing longer than a man's hand Redlichia was the largest trilobite in these Gondwanan waters, but it was still well-armored with defensive spines. There was a good reason for this.

Top predator in the Cambrian ocean was a giant arthropod called Anomalocaris. Anomalocaris was an animal that grew to over six feet in length.

JOHN PATERSON: So this thing would have been fluttering around in the surface waters, looking for, for probably other arthropods.

RICHARD SMITH: Clearly the evolutionary arms race had begun. While the trilobites went on to reign for another 250-million years, Anomalocaris swam into oblivion by the end of the Cambrian.

Back on land, and with no botanical protection, the high peaks of the Petermann Ranges, in central Australia, were wearing away. For a hundred-million years or more, rivers had been tumbling from their bare snowy peaks.

These days, the Petermann Ranges are little more than a fading blue blip on the central Australian horizon, but their legacy lives on. As the ancient waters poured out of the mountains, they carried the raw materials for two of Australia's most treasured rocky landmarks.

The rivers that roared out of the mighty Petermann Ranges, which once towered on the horizon, swept their heavy load of worn-away mountain as far as the water would carry it. A lot of it ended up here, to form the magnificent bedrock of Kata Tjuta.

The smooth domes of Kata Tjuta are the eroded remnants of a thick conglomerate of rounded river cobbles, dropped by the fast-flowing water. A lighter load of sand was carried further afield. It ended up here, about 20 miles away, where rivers slowed as they met the shore. This is how Uluru, the great red rock in Australia's desert heart, began life, as wet sand from a recycled mountain range, settling at the edge of a now vanished Cambrian Sea.

The lights went down on Cambrian Australia with the stage set for the next great drama in the story of the earth. And the cast was already gathering out to sea.

Despite the explosion of life going on in the sea, if you'd taken a walk on a Cambrian beach, you probably wouldn't have noticed much going on at all. Perhaps a trilobite might have tickled your toes, but apart from the wind and the waves, this was a silent world. There was still no life up there, on land.

It would not stay this way for long. The seas, now bursting with life, were set to spill their cargo onto the bare earth, and Australia was ripe for conquest.

Australia: Life Explodes

PBS Airdate: April 17, 2013

RICHARD SMITH (Biologist): Over four-billion years in the making, an island adrift in southern seas: it's Australia, the giant down under; a young nation with all the gifts of the modern age, but move beyond the cities and an ancient land awaits, one nearly as old as the earth itself.

Australia is a puzzle, put together in prehistoric times. And the clues that unlock the mystery can be found scattered across Australia's sunburnt face.

I'm Richard Smith, and this is an amazing country. I'll show you that every rock has a history, every creature a tale of survival against the odds. Join me on an epic journey across a mighty continent and far back in time.

Of all continents on Earth, none preserve the great saga of our planet and the evolution of life quite like this one. Nowhere else can you so simply jump in a car and travel back to the dawn of time.

In this episode: the world above water has sat silent and lifeless, but now armies storm the beaches, and biology conquers the world. It's the battle for life on Earth, the struggle for legs and lungs, sunlight and shelter, even the quest for sex. From Australia's ancient stones comes the story of our world: Australia's First 4 Billion Years: Life Explodes, right now, on NOVA.

If Australia seems a little tired and worn, it's because she's seen a lot happen over the course of her long life. In the last episode, our journey down the road of time began with the earth's fiery birth, four-and-a-half-billion years ago. We passed the first fumbles of life in the waters skirting Australia's ancient shoreline. Along the way, we've seen the planet change from poisonous to pleasant and the first animals begin to swim in the seas. Yet, save for a thin smear of slime and bacteria along the soggiest of margins, all the continents themselves had lain bare for over four-billion-years. In terms of the lifetime of a continent, Australia, and the world around it, is still an infant, still attached to its motherland—the great supercontinent Gondwana—and still a blank canvas on land.

GPS DIGITAL VOICE: Your destination is the Paleozoic.

RICHARD SMITH: Now, with 90 percent of Earth history behind us, it's time for conquest. The tremendous explosion of life that began in the oceans of the Cambrian was still going strong at the dawn of the Ordovician, the second of the six great periods that make up the Paleozoic. And it was in Ordovician oceans that a second wave of animal experimentation began, as well, one that ultimately would lead to the first Australians coming ashore. With the seas now crowded with life, the first tentative footsteps onto land were not far away.

Now, at the time, Australia was just one of an exotic collection of lands, including India, Africa, South America and Antarctica, that, today, we call the supercontinent Gondwana. Australia's position was just about here, right on the tip, just north of the equator and mostly under water.

Oceans were rising around the planet, and seawater flooded in across parts of central Australia. At the time, the sea of sand we know today as the Simpson Desert was slap bang in the middle of the Larapinta Seaway, a tongue of warm ocean water that licked right across the country. Back then, this bouncy drive would have been a bumpy boat crossing. As the rising waters swept in, they carried a rich bloom of plankton, food for some of the earliest fish to swim in the sea. And they swam right here, right above me.

The last vestiges of the old Larapinta sea floor lie tumbling from the top of the mesa-shaped hills of the Simpson Desert. Even in the best of seasons, like this, the Simpson is a harsh unforgiving landscape. Now, you probably wouldn't expect to find the world's earliest fish in the dead center of the driest inhabited continent on the planet, today. But it was on the side of this hill in the Simpson Desert that the fossil of Arandaspis lay, waiting to be discovered.

We only know Arandaspis from the bony head plates and body scales it left behind, enough to tell that this was a fish with a simple tail and no real fins. Nor did fish like Arandaspis have jaws or even teeth. They probably just slurped in whatever morsels they could find.

But don't underestimate the significance of this fish. This was an animal with a backbone. It's one of the first vertebrates, so we can all trace our ancestry back to an animal like this.

But giant invertebrates ruled these Ordovician seas, and to them Arandaspis was just a bite-sized snack.

While the first fish took to swimming out of danger, their invertebrate foes would soon be flexing their leg muscles in a different way; time to put the foot down and head for the seaside in the Silurian.

On a remote stretch of the Western Australian coast, the 21st century Indian Ocean eats away at an ancient Silurian shoreline. Wind and water have exposed the burrows of long-gone animals in the sandy coastal cliffs.

The original inhabitants of the burrows remain a mystery, but not the predators attracted by such rich pickings along the prehistoric shoreline. Clues to their identity are revealed in the rocks of nearby Murchison Gorge. Here, the river has sliced deep into the Silurian past.

The Murchison Gorge, back in the Silurian, wasn't a gorge at all, of course. It was a vast estuarine flood plain, with rivers winding down from the hills in the distance, carrying sand into the sea. But for the first time in the history of the planet, those Silurian shorelines down there were alive with animal activity.

This may not have been a good time to take the kids to the beach. Armies of sea scorpions were massing in the shallows. Known to paleontologists as eurypterids, some of these intimidating arthropods grew as long as a man is tall, and they bristled with armored legs and fearsome claws.

Far less threatening was this bloke. Kalbarria was probably an ancestor of modern crustaceans and grew about as long as a king prawn. Whether in search of food, a safe place to mate or simply to avoid the nasty neighbors, Kalbarria clambered ashore, and left clear imprints of its many tiny feet in the rocks.

A descent into Murchison Gorge takes you back to those ancient Silurian shorelines.

Down here, it soon becomes clear that the sea scorpions followed Kalbarria ashore.

MICHAEL PAXMAN (Kalbarri National Park): This is what we call track central.

RICHARD SMITH: I can see why. Yeah, there are tracks everywhere.

MICHAEL PAXMAN: This is probably the best site in the park to look at these eurypterid tracks.

Our animal's come through here.

RICHARD SMITH: So, in shallow water.

MICHAEL PAXMAN: Shallow water.

RICHARD SMITH: Okay, been slipping and sliding a bit as it comes around the corner.

MICHAEL PAXMAN: That's exactly right.

RICHARD SMITH: But here, I mean, I can see clearly it's a kind of sloppy-looking track here. But once you come over here, you start seeing really discrete footprints, clear graphic demonstration of a creature walking out of the water and onto dry land.

MICHAEL PAXMAN: And where we are, here, in the depth of the gorge, we're in the oldest of the Silurian sediments in the, in this area.

RICHARD SMITH: Quite an historic little spot you've got here.

MICHAEL PAXMAN: Very. Very.

RICHARD SMITH: These trackways offer some of the oldest evidence for animals on land. And even though these formidable beasts could not stray far from the water's edge, a beachhead had been established. So, this seems to be how the animal invasion of the land began, with a scary assortment of arthropods with attitude slinking and scuttling ashore onto the wet sands of a new frontier.

But this wasn't just a continent to exploit; there was a whole planet for the taking. Waiting beyond the breakers were all the wide brown lands of Earth.

Australia, already under animal assault found itself center-stage for the waves of invasion and conquest that would follow.

But animals were not going to get far inland without help from plants. They, too, came out of the sea: first as slime, then as low-spreading things that clung to dampness. Seaweeds captured the shoreline, then tiny forests of lichens, liverworts and mosses pioneered the move inland.

Today, we take for granted the plants around us. It's their oxygen we breathe, their food we eat, but the land can be a tough, dry place to live, and any plant going to make it big out here needed a thick skin and a little internal fortitude. Just such a plant first took root somewhere around here.

If you thought that this was just another ordinary roadside cutting, on a pretty, but ordinary, country road, well, of course, you'd be dead wrong. It was here, near Yea, in Victoria, that fossils of some of the world's earliest land plants were found. Indeed, these rocks contain the first signs of the greening of Gondwana.

Just amazing.

This is Baragwanathia, possibly the oldest true land plant in the world.

Not much to look at perhaps, but with green leaves and a stem to carry sap internally and to support its weight, the world above water was its oyster. In life, it would have looked much like this. This is a lycopod, or club moss, as was Baragwanathia, rising out of the water in a coastal bog in Queensland, today.

These are the direct descendants of the green revolutionaries who changed the face of the planet. If you look closely, you can see many of these Silurian-type plants still clinging on in damp corners around the country: here a rainforest Selaginella, a tropical tassel fern; a club moss in Tasmania; even a Psilotum in Sydney.

Plant life had, by now, engineered a solution to the ultraviolet radiation that had been sterilizing the earth's surface, an ozone layer built from excess oxygen. The low-spreading thickets provided the perfect humid cover for other arthropod forms, like millipedes, centipedes and mites, to make the transition to land complete. Some mollusks even brought their own homes, because it was still not a very welcoming place.

While life was exploring the fringes, most of the Gondwanan supercontinent was dry, probably still quite bare, and almost certainly windy. The Larapinta Seaway had receded, leaving much of what is now central Australia resembling the Sahara Desert.

And that desert became mountains. Titanic tectonic forces, operating over a span of 150-million years, buckled the earth and pushed great folds of rock into the air. In their heyday, central Australia's MacDonnell Ranges would have been a mountaineer's dream, as high, it's thought, as any on Earth today. But Australia would never experience mountain-building on this scale again.

After a near-eternity of erosion, the diminished remnants of the MacDonnell Ranges still run in long, jagged wrinkles across the heart of Australia. From the air, they protrude into this ancient landscape like the bony skeleton over which the dry skin of a tired continent is draped.

All other continents boast mighty mountain ranges—the Rockies, the Alps, the Andes, the Himalayas—but they're all relative newcomers and mostly still growing. What sets Australia's landscape apart is its venerable antiquity and its great flatness.

LISA WORRALL (Zeus Resources Limited): Australia is actually quite remarkably flat, and when you look at it from space, it's not just flat but it's apparently saucer-shaped.

RICHARD SMITH: It's a saucer that holds many secrets for geologist Lisa Worrall.

Her interest is not so much the bedrock of the Outback, but the story of all its eroded remnants, accumulated over a vast gulf of time.

LISA WORRALL: We know parts of Australia have been exposed for millions, if not billions, of years. We're partway through an ongoing geological story. The rivers that, in Australia, mostly drain inland are actually losing or have lost the ability to carry sediments out and down into the seas, so inland Australia is filling up with sediments.

RICHARD SMITH: Outback Australia is drowning in sand. Head towards the coast, in any direction from the red center, and you cross oceans of these old weathered sediments. It's the sort of landscape you should expect from the flattest continent on the globe.

Travelling northwest, it's 700 miles before you reach the next significant patch of high rocky ground: the Kimberley. While mountains were still pushing skywards in the continent's heart, up here, in Purnululu National Park, others were already wearing down to nothing.

Epic tales of erosion and recycling lie behind most geological features in the Australian landscape. The sands and gravels that make the Bungle Bungle Ranges started arriving here about 375-million years ago, dumped by rivers that wore away highlands far older and now long gone.

This landscape was already secondhand, long before the rocks began eroding away into the famous striped beehive domes we see today. The distinctive striping of the rocks here is a dead giveaway to how the Bungle Bungles were formed, layer by layer, as mighty rivers washed sediment from distant mountain ranges to fill the basin. This unfolding landscape is a two-toned testament to change, left as a parting gift, by rivers that ran down into a Devonian tropical sea.

Three-hundred dusty miles to the west of the Bungle Bungles and you can run down to that same ancient sea, once home to some of the most spectacular tropical reefs on the planet.

Surprisingly, you can still visit these reefs today.

I'm standing at the base of the great Devonian Barrier Reef. These towering limestone cliffs were once towers of life, rising into the clear sunlit waters of a colossal reef system that once circled the Kimberley.

In both size and significance, the Devonian reef rivaled modern Australia's Great Barrier Reef. Its limestone ramparts were once festooned with crinoids and corals, sponges and sea squirts, and many other creatures still found clinging on in tropical waters. That Devonian life is gone, but the great reef walls still stand to this day.

It's easier to see from the air.

In the same way that the Great Barrier Reef fringes the Queensland coast today, the Great Devonian Reef skirted in a sweeping curve around the Kimberley hinterland, for perhaps 600 miles. Reef after reef line up across the landscape, as if a giant bathplug had been pulled.

At Tunnel Creek, one such stream has carved its way right through the Devonian limestone range. It's a deliciously cool change from the sweltering heat outside and offers dark access to the very heart of the reef itself.

A whole suite of reef-building organisms built this great Devonian Reef above me. You can see a lot of their ghostly remains in the rocks, still: sponges, stromatolites, corals, strange extinct things called "stromatoporoids." But the real stars of the show, here, weren't the things that made the reef, but the things that swam around outside it, things with fins, because this was the great "Age of the Fishes..

It was in the Devonian that, for the first time, fish filled the oceans; fish of all shapes and sizes, just not quite the shapes and sizes we see today.

Like the reefs themselves, the fish of the Devonian northwest are amazingly well-preserved, protected in limestone nodules scattered across nearby Gogo Station.

You don't get a lot of bites around here. About one nodule in every thousand yields a good fossil strike. But whenever you catch a Gogo fish, it's always something special.

GAVIN YOUNG (Australian National University): Oh, wow.

KATE TRINAJSTIC (Curtin University): That's a lot of bone.

GAVIN YOUNG: That's all bone, there; some very large plates.

KATE TRINAJSTIC: So, what do you think that is, Gavin.

GAVIN YOUNG: It's clearly a large placoderm, probably a big arthrodire.

RICHARD SMITH: Kings of the Devonian seas were the placoderms. Fish had moved on since the days of Arandaspis. Now they had jaws, fins and teeth to go with their bony head plates.

GAVIN YOUNG: The front part of the body was covered in these bony plates, and then the tail would be pretty much shark-like. They were, in fact, very agile, successful predators, and they had a highly developed sensory system.

Some of them had electrosensory perception, like modern sharks and rays.

RICHARD SMITH: Many of these fossil features have been preserved in fabulous 3D.

KATE TRINAJSTIC: Oh, look. There's some ridging.

RICHARD SMITH: The Gogo nodules have protected the fossils from being crushed.

KATE TRINAJSTIC: Do you think it might be a Holonema.

A nice bath in acid's going to clear it up.

GAVIN YOUNG: Even soak it in some water and scrub it with a toothbrush.

KATE TRINAJSTIC: If I'm not getting a shower at night, this fish certainly isn't.

RICHARD SMITH: It's only once the limestone nodule is dissolved away, in acid in the lab, that the fossilized fish within come back to life in astonishing detail: scales, teeth, eye sockets, brain cases, bones and fin rays. The fish are all so fabulously well-preserved for their age, that even soft body bits can be made out.

In more ways than one these are pretty sexy fossils.

KATE TRINAJSTIC: Well, this one, here's particularly interesting, because it's one of the few male fossils that we have. And we can tell that because it has this clasper.

RICHARD SMITH: Like in a shark.

KATE TRINAJSTIC: Very much like a shark.

RICHARD SMITH: This bony tube structure is the oldest confirmed male appendage, a fishy private part for impregnating a female.

The Devonian was an important time for vertebrate life, with many biological experiments underway, including the all-important vertebrate sex. Even today, sex in the sea can be a bit of a hit or miss affair, a tradeoff between precision and plenty. Without coupling and live birth, vulnerable progeny sink or swim on their own, not a strategy destined for success on land.

This is a portrait of the world's oldest preserved mother with child, and we have the fossil to prove it.

KATE TRINAJSTIC: This is perhaps our most famous discovery, to date. This is the mother fish, and this is the real, kind of, clincher we had that you could have live birth. And it's this little structure here, right around the bottom, and that is the umbilical cord, which is attaching the mother to her unborn embryo.

RICHARD SMITH: My goodness, that's the world's earliest umbilical cord we know of.

KATE TRINAJSTIC: It is. It is the world's earliest evidence of live birth, in any vertebrate.

RICHARD SMITH: Our backboned ancestors were making all the right moves, already on the road to becoming social, smart and sexy. And they were everywhere.

As rain fell on Australia's newly constructed east, rivers ran back down towards the sea, filling the freshwater lakes and backwaters of the new coastal landscape. Throw a line into one of those Devonian rivers and you would have caught plenty of fish that looked almost identical to this.

Whoa, hi, big guy. Oh, look at you! Aren't you something special.

Now this is something truly special, a living link to our fossil past. It's the Queensland lungfish, Neoceratodus forsteri, and I'm trying to hold him, I hope. Now, he is the most primitive of the handful of lungfish that still swim on Planet Earth. Think about it for a moment. These guys were already ancient history a hundred-million years before the first dinosaurs walked the earth. And if you're worried about that "fish out of water" thing, these guys are called lungfish for a reason: they're built for it.

There you go, matey. Off you go. Thank you.

When lungfish moved from the sea into fresh water, in the Devonian, they brought with them the ability to breath with or without gills when the going got tough. It's a skill that still stands these remarkable living fossils in good stead. They live on in just a few river systems in South East Queensland. And when oxygen levels fall, they can switch to gulping air from the surface. It's a strategy that has doubtless allowed them to struggle through more than one Australian drought.

Not all fish have been so lucky.

As far as we can tell, drought is a problem that has plagued the country for at least 360-million years. We know this because, in 1955, the local council sent a bulldozer to smooth out a bad bend on the Canowindra to Gooloogong Road. Well, the bad bend in the Canowindra to Gooloogong Road is still here, and you wouldn't know it to look at it, but I've just parked right on top of one of the most spectacular Devonian freshwater fish sites in the world.

The road works inadvertently lifted the lid on Australians' oldest known Outback waterhole. When a paleontological team returned to open the site, thousands of fish tumbled out. They were lying on the slabs, just as they had been the day they all died together, when their water hole dried up.

Like their saltwater Gogo cousins, many were armor-plated placoderms. There were lungfish here, as well, and another, related, group of fishes with four-lobed fins, that we humans should be very thankful for.

Of the 4,000 or more fish uncovered on these Canowindra slabs, this one is special. It's been given the name "Canowindra grossi," after the town, of course, but its real claim to fame are the features that it shares with those fish-like animals that were leaving the water behind. A single pair of external nostrils suggests it, too, could breathe with both lungs and gills, and it was one of the lobe-finned fish, a group with four limb-like fins with a bony internal structure we can recognize in our own arms and legs.

It's not hard to imagine that somewhere in the drying Devonian waterhole at Canowindra, at least one of those fish might have got away by walking onto land. And this is why: hard evidence, in the form of fossilized four-legged footprints, of about the same age, and found near the Genoa River, in Victoria.

It was a different Genoa river, but these early fish-like tetrapods, about three feet long, were among the first animals on Earth to feel the sand between their toes.

It's not hard to see how the evolution of walking limbs might have come about. Many Australian fish species today are still testing out ways of getting about without swimming. This is the aptly-named "handfish," hopping and skipping its way along the Derwent Estuary in Tasmania; and this, that master of the tropical mangrove, the "mudskipper..

However they managed it in the first place, amphibians soon walked out into the botanical wonderland of the Carboniferous. The Carboniferous saw all sorts of new plants putting down roots and pumping out oxygen, at levels the planet had never seen before. Huge forests, especially in the northern hemisphere, helped push up oxygen levels in the atmosphere, perhaps 50 percent higher than today.

The extra oxygen saw some invertebrates grow to enormous sizes. It allowed millipedes the size of snakes to scuttle across the land and insects as large as seagulls to take to the air.

The rich insect pickings on offer must have favored the spread of the amphibians, now moving through the landscape. But like their froggy descendants today, these ancestral four-legged animals needed to return to water to reproduce.

Sometime in the Carboniferous, the first reptiles overcame this limitation. Wrapping their eggs in a membrane blanket with a hard outer shell, reptiles could take a watery egg with them on their travels. It was a solution so successful that it allowed the many contemporary "Lizards of Oz" to still claim the arid Australian Outback as their own.

There was yet another Carboniferous legacy left out here. The greening of the earth began to at least partly turn Australia red. The highly oxygenated atmosphere began to rust the iron rich soils and rocks of the Outback. And some rocks out here are bigger than others.

It's very impressive.

LISA WORRALL: It's a fabulous monolith isn't it? It's justly famous for being the biggest rock, the largest bit of rock, lump of rock in the world. And it's just gorgeous.

RICHARD SMITH: And it's very red, the color of weathered iron minerals, like hematite.

LISA WORRALL: Many of the rocks of Australia are rusted. We know that we had oxidizing rocks back to around the Carboniferous. That coloration in the landscape is very old and very persistent.

RICHARD SMITH: But at the end of the Carboniferous, just as world domination lay within the reptiles' grasp, the changing world threw up another great climate challenge. The drift of Gondwana saw Australia heading south and getting colder. It was more than just the location; the earth had slipped into another ice age, and Australia was covered in more ice than it would ever see again.

By the time we reached the Permian, a deep chill had settled in. Ice carved its calling card on the country, nowhere more clearly than the Fleurieu Peninsula in South Australia.

The bedrock here was scoured by glaciers. All of these long scratches and grooves in this smooth surface were gouged by rocks and debris being dragged along on the bottom of an ice sheet flowing in this direction.

What these rocks are telling us is that, clearly, if you look to the south of Australia, back in the Permian, you wouldn't have seen the open ocean we see today. If you looked back that way, you would have seen the mountains of Antarctica.

It's incredible to think that if you travelled to Australia in the early Permian, the landscape probably looked much like this, over at least the southern half of the continent. Evidence for ice can be found stretching across the country, from the Kimberly to the coast of Tasmania. But this cold landscape was not frozen solid like Antarctica; it was seasonally cold, more like a northern Alaska or Canada.

Well, Permian Australia might have been freezing cold, but it was far from lifeless. These remarkable rocks on Maria Island, are just stuffed to the gunnels with shellfish. And nearly every one of the animals in the rocks here and in the rocks behind me and in the cliffs in the distance, belong to one species of clam: this one, called "Eurydesma..

What Australia's Permian ocean lacked in diversity it made up for with abundance. Life crowded the sea floor.

It was the same story on land. And the proof can be found hidden underneath Australia's moist eastern seaboard, much of it right under modern Sydney. Beneath the Eucalypt forests that surround the city of Sydney today, lie cool-climate forests far more ancient.

ELEVATOR OPERATOR: Welcome underground, gentlemen.

RICHARD SMITH: Ground floor: the Permian.

I'm heading deep into a coal mine, at Helensburgh, on Sydney's southern outskirts. The seams of rich black coal here have been mined for longer than any other in the country.

What you are looking at, here, is the exhumation, half a kilometer underground, of the dead black graveyard of a vast swampy forest that once stretched right across the Sydney basin. It's hard, messy, noisy work, but there's treasure in this coal, the raw energy of fossilized sunlight.

Half the energy used to light Australian homes, fuel industry, cool beer and power this program comes from Permian plants, buried faster than they decomposed, over a quarter-of-a-billion years ago. When scientists looked closely at these coal seams, they found something not seen in the Australian forest growing so far above me, today. The fossil leaves they encountered were found in alternating, repeated layers. Every autumn, it seems, these now blackened Permian coal forests were once a riot of color.

One tree above all others dominated the Permian forests: Glossopteris. Glossopteris had solved another part of the problem of reproducing on dry land, by encasing its embryo in a protective seedy shell, so successfully, it turns out, that fossilized Glossopteris leaves are the botanical signature of all Gondwanan lands.

The planet had come of age in the Permian. Here was a world with great oxygen-producing forests, inhabited by animals with four legs; insects had taken to the skies; and the seas were brimming with animals.

Life on Earth was going swimmingly well, and then, suddenly, everything went diabolically wrong.

Well, the Permian came to a sudden and very sticky end, right here at the greatest extinction boundary in the planet's history. Now, this black coal is the last coal to have been deposited anywhere on Earth, in the Permian, the last of the great Gondwanan Glossopteris swamps. But it also marks the bitter end for over 80 percent of all species alive on the planet, at the time. This truly was the world's greatest cataclysm. This figure is conservative. Some estimates have 95 percent of all species dead and gone, wiped out in a geological blink.

The trigger, it seems, did not come from outer space but from underground. It's now thought massive volcanic eruptions in Siberia pushed CO2 levels sky-high, and the planet into a runaway greenhouse crisis. These were the days when our living earth nearly died. Acidified and stagnant, great swathes of the ocean festered; toxic bacteria took over from plankton; and deadly hydrogen sulfide spilled into the skies.

But with change, even of the calamitous kind, comes opportunity, and the earth would soon echo to the thunder of giants.

Australia's First 4 Billion Years: Monsters

PBS Airdate: April 24, 2013

RICHARD SMITH (Biologist): Over four billion years in the making, an island adrift in southern seas: it's Australia, the giant down under; a young nation with all the gifts of the modern age, but move beyond the cities and an ancient land awaits, one nearly as old as the earth itself.

Australia is a puzzle, put together in prehistoric times. And the clues that unlock the mystery can be found scattered across Australia's sunburnt face.

I'm Richard Smith, and this is an amazing country. I'll show you that every rock has a history, every creature a tale of survival against the odds. Join me on an epic journey across a mighty continent and far back in time.

Of all continents on Earth, none preserved the great saga of our planet and the evolution of life quite like this one. Nowhere else can you so simply jump in a car and travel back to the dawn of time.

In this episode: out of the chaos of disaster rises a new world order, ruled by reptilian tooth and claws. It's the age of dinosaurs, down under. Join me, as I retrace the footsteps of predators and prey and dive into a long lost sea.

From Australia's ancient stones comes the story of our world: Australia's First 4 Billion Years: Monsters, right now, on NOVA.

It's a long journey back to our modern world from distant ancient Australia. From the birth of the earth to the present day, the road of time stretches a mind-boggling 4.6-billion years. It helps to imagine, just for a moment, that this car can travel through time.

I set the controls for a million years per minute, that's 60-million years of history for every hour we travel down the road. You want to see the real old Australia? It's quite a ride.

G.P.S. VOICE: Your destination is the Mesozoic.

RICHARD SMITH: Travelling at a million years per minute, the entire story of Australia and the planet is condensed into a little over three days solid driving.

And for most of those first three days we have roared through the infancy and childhood of the Australian continent. And now, with 70 hours of my journey behind me and only another four to go, we've arrived at the start of Australia's wild adolescence.

It's the Mesozoic. It's the most familiar of all geological eras and for good reason. It's in the Mesozoic, home of the Triassic, Jurassic and Cretaceous periods, that dinosaurs ruled the earth. But despite such world domination, evidence for their conquest of Australia has been a little thin on the ground, until now: time for the Age of Dinosaurs, down under.

The Triassic, the first of the three great periods that made up the Mesozoic, got off to a pretty shaky start. The Permian crisis, the world's most catastrophic extinction event, was over, but gone with it was perhaps 95 percent of the biological diversity of the planet. Around the world, life had been all but wiped out in the sea and devastated on land.

Yet, somehow, out of the carnage and confusion 5of that devastated world rose a new one, and with it, the dramatic sandstone landscape of Sydney.

TIM FLANNERY (Macquarie University): I think, Richard, this would have to be one of the best places to see the Sydney sandstone. There is the Pacific Ocean, there is North Head, over there; there is the entrance to Sydney Harbor, just behind us there. Over here is the gap.

RICHARD SMITH: And a lot of rock underneath us.

TIM FLANNERY: There is about 250 meters solid sandstone.

RICHARD SMITH: Biologist Tim Flannery knows the landscape of my hometown well. Sydney, it seems, was built on the aftermath of disaster.

TIM FLANNERY: We would have been standing, when this sandstone was laid down, in a post-catastrophic world. We've had the great disaster of the Permian extinction, with life almost extinguished, 95 percent of all species gone.

RICHARD SMITH: Even plants struggled to recover.

The colorful forests and rich coal swamps at the Sydney basin had gone, and over the next 20-million years, the lush world of the Permian was buried deeper and deeper in sand.

TIM FLANNERY: There's been some recent studies suggesting that this sand here, particularly, may have come from as far away as East Antarctica, and that is a massive distance.

RICHARD SMITH: Storms raged on those distant mountains, and rivers thundered from their denuded slopes, carrying unimaginable quantities of sand northwards, across vast spreading flood plains.

TIM FLANNERY: This rock talks to me of a time when life was slowly recovering, but there is not even enough life and vegetation to hold the banks of the river together. It's just this great braided system running across the landscape.

I can just imagine standing there, seeing these ripples, six meters high, imagining this world where the physical processes of the planet are just laid so bare. These sand grains saw that. They, they…the sun that was shining down on the planet then struck those sand grains that we are standing on now. And it's that great physical reminder. That's why I love geology, you know? That you know that that rock was there at the time, 230-million years ago.

RICHARD SMITH: Shifting sand has turned to solid stone, and the debris from the end of the Permian world is now the foundation for a new one. Now, after waiting quietly in the dark for some 230-million years, the lost sands of Antarctica have a new job, as the bedrock and building blocks of a great global city.

Sydney is defined by its Triassic geology, from the warm glow of its stone buildings to the shape of its harbor. The sandstone dictates everything, from the flow of traffic to the form of its native flora. The sandstone cliffs stand hard and proud against the Pacific Ocean and weather into the soft golden sands of the surf line. The sand also buries the Permian peak lands, allowing them to become the coal that powers the city. And rising to the west, this same sandstone forms the rocky ramparts of the Blue Mountains and the Great Dividing Range, all of this a legacy from the dark days when the earth nearly died.

It was the sudden lurch into an intense greenhouse climate that seems to have triggered the initial disaster at the end of the Permian. A series of wild climate swings then plagued the early Triassic, before the planet finally stabilized. And even when it did, temperatures still simmered. Conditions would have remained pretty hot and dry, no matter where you went on the planet.

Australia was still part of a supercontinent—Gondwana—but Gondwana was now part of a super-supercontinent called Pangea, where all lands were one. Given a decent four-wheel drive, you really could have gone just about anywhere.

Australia had joined the wild bunch, though it was very much at the bottom of the continental pack. Australia lay near where Antarctica does today, but this was a South Pole in an ice-free, greenhouse world: there were ferns and gingko trees, freshwater fish and giant carnivorous amphibians.

But the Triassic earth belonged to reptiles. Some were taking to the air, others to the sea. Walking the land were lizard-like reptiles, mammal-like reptiles and the first dinosaurian reptiles, as well. Though we know these early dinosaurs roamed across southern Gondwana, they've left almost no trace here in Triassic Australia.

But the evidence for Australian dinosaurs is out there, if you know where to look.

The old gold-mining town of Mount Morgan, in Central Queensland, is one such place. When the old miners excavated clay from a nearby hill, what they dug away was the mud that once filled a Jurassic lake.

So this was all lake, a lake deposit here?

FEMALE: It was, yes. So we're in underneath where the dinosaurs walked, on the edge of that freshwater shallow lake.

RICHARD SMITH: Left behind in the rocky ceiling are the three-toed imprints of dinosaurs that walked on the lake's muddy fringe. The ghosts of dinosaurs past still haunt these caverns.

FEMALE: There's a few up here.

RICHARD SMITH: Oh, yes, yes, yes.

These footprints, and those from other mines, help flesh out a Jurassic Australia, rich in forests and waterways.

I'm standing in what was the muddy edge of a lake, and up there, on the lake's surface, a Theropod once walked above me, about a hundred and 90-million years ago; an imprint as clear as day.

But Australia is big and old and red and flat, this is a geological landscape that has kept its Mesozoic secrets well-hidden.

The botanical landscapes Australia's dinosaurs walked in, though, are much easier to experience. You can still walk in them today. The Mesozoic was a great time for plants. The earth was an ice-free greenhouse world: warm, wet. Thick forests spread around the globe, and the southern lands of Gondwana were no exception. Cycads, ferns and gingkoes were common and had now been joined by the tree ferns that still abound in the rainforests and gullies of eastern Australia. But the standout trees of Mesozoic forests, worldwide, were the giant conifers.

Luckily, some of those giant conifers are still with us. This towering sentinel is a Queensland bunya pine. And it's remarkable, not only for it's great size, but because it's so-little changed.

The bunya, oak and Kauri Pines of eastern Australia are well-known living fossils from the days of the dinosaurs. But in 1994, the ultimate "pinosaur" was discovered: the Wollemi Pine, a green giant, 130-feet tall and hiding only a hundred miles from Sydney.

Here, in a couple of secret canyons are less than a hundred of perhaps the oldest surviving tree species in the world, the spitting image of fossils from as far away as Antarctica.

Today, the great conifer forests of Australia are gone, but the few surviving pockets allow you to dream of the days when you could have driven from coast to coast with not a eucalyptus leaf in site.

The Mesozoic earth was restless. Like a teenager with a growth spurt, it was on the move again. The supercontinent Pangea was breaking up, leaving Australia, still attached to a remodeled Gondwana, in the Southern Hemisphere.

And around the end of the Jurassic, a little extra remodeling was applied from space. A falling rock, in the shape of an asteroid or comet, slammed into central Australia It was a bull's eye that you can still see, almost bang in the middle of the continent. As impressive as it is, Gosses Bluff, or "Tnorala," to give it its indigenous name, is a shadow of its former self. Most of the original 13-mile-wide crater has been worn away. What's left is merely the bowl, punched deep into the earth, below ground zero. Still, the ring of low hills gives a pretty good hint at the scale of utter devastation that must have been visited upon the land for at least 60 miles in every direction.

Sometimes, you get a chance to truly grasp the scale of past geological events, and when you do, it's truly humbling.

It wasn't the Gosses Bluff impact that did in the dinosaurs, but it was a portent of dangers to come.

When dawn broke on the Cretaceous, dinosaurs still had their claws on the continent, from one side of it to the other. It's been a long wait, but, finally, the 21st century is throwing new light on the Australian dinosaur story. For years, the ancient secrets of the Kimberly coastline, near Broome, have been guarded by extreme tides and extensive crocodile-inhabited mudflats. It makes for an easy place to imagine what might have been walking the land in the primeval past.

But imagination, alone, is not required here. The giant beasts of the early Cretaceous have made their presence clear to us.

The first clear chapter in Australia's rather secret history of dinosaurs starts here, on the beaches near Broome, in the Kimberly. Back then, this was a vast coastal forest, running down to flood plains and estuaries near the sea, not radically different from the tropical mudflats of today, except for the 15 or so species of very large dinosaurs that have left their marks in the rocks here.

A rich reptilian community once stomped this landscape. Dinosaur footprints stretch over 60 miles of coast. They must have been everywhere. Even the suspected Stegosaur left its mark here: one of only a handful of such five-toed prints in the world. But the largest and most abundant footfalls belonged to the towering vegetarian sauropods. And this is the trackway of one large sauropod that came wandering past Broome about 132-, 135-million years ago: big footprints, one there, another one there, a big footprint here; and interspersed amongst them, some smaller footprints, thought to have been made by a calf, wandering with its mother. There is little evidence, though, for parental care in sauropods, and once you reach this sort of size, little need for it. Finding enough to eat was probably a bigger concern than avoiding predators. But for most Australian dinosaurs, day to day life was a hazardous experience, as a small herd discovered 95-million years ago, near Winton, in Queensland.

That moment is frozen in time, here, at Lark Quarry, the site, it's been thought, of the world's only recorded dinosaur stampede. Picture the scene here, one ordinary day in the Cretaceous. This was a broad muddy spit, running down into a lake just over there. Now, sometime during the day, a mixed herd of small dinosaurs wandered across the mud to take a drink at the water's edge. Here you can see the very clear footprints of a small chicken-sized meat-eater, and, here, the emu-sized tracks of an ornithopod dinosaur. But behind me, probably more or less where the wall is, was the start of a forest of tree ferns and gingko trees.

These rich forests, dominated by conifers, provided shelter and food; and cover for a meat-eater. Even for a weary dinosaur, the Cretaceous was no time for complacency. Now, if you popped your head up and looked back this way, you would have seen one very large, very hungry Therapod, head down and heading your way. In the pandemonium that followed, a hundred and fifty terrified dinosaurs scattered in all directions, sliding on the mud and crashing into each other as they raced to reach the relative safety of the forest beyond.

Footprints, though, can only ever tell part of the story. Bringing Australia's true blue dinosaurs to life needs bones. And, finally, those bones have also started turning up.

DAVID ELLIOTT (Australian Age of Dinosaurs Museum): Here's your coffee.

JUDY ELLIOTT (Belmont Station): Oh, thank you.

DAVID ELLIOTT: How is it going?

JUDY ELLIOTT: Slowly coming together, very, very slowly.

RICHARD SMITH: They've come to occupy a very special place in the lives of sheep farmers David and Judy Elliott.

DAVID ELLIOTT: You've only got 10,000 pieces to go.

JUDY ELLIOTT: Yeah, I'm doing really well.

RICHARD SMITH: And, yes, that is a dinosaur on their kitchen table.

JUDY ELLIOTT: It's a pile of rock that's got tiny bones in it, and we've dubbed it "Chook" or "Chooky," because that is about the size of the animals that the bones relate to. So it's Chooky.

RICHARD SMITH: Hunting dinosaurs was never part of the Elliotts' business plan, but they are fast becoming experts.

DAVID ELLIOTT: This dinosaur site that we are going to is probably the most exciting and it's definitely the most significant of what I've found, so far. And it's a place that's produced a tremendous amount of material in quite a short time.

RICHARD SMITH: The Elliotts began their dinosaur odyssey by accident, pretty much by tripping over the bones of some of some dead ones on their property.

So, Dave, this is a big hole in the ground?

DAVID ELLIOTT: Yeah. Here we are. This is where it all started.

If you can imagine 95- to 100-million years ago, we, were sitting in a lush rainforest area. Look back in the north, and where we have nice flat open grassland, so that would have been an inland sea. And what we had were these big rivers coming in and bringing silt, and just depositing silt so slowly that sea was being pushed back to the north. And the rivers would have been full of lungfish and turtles, big crocodiles and freshwater fish.

RICHARD SMITH: From what they have seen so far, David's convinced the dinosaurs being unearthed have a unique Australian pedigree.

DAVID ELLIOTT: The dinosaurs out here are totally different, and that's so true for just about everything Australian, isn't it? Even us, you know? We're a little bit different aren't we?

RICHARD SMITH: Before the dinosaurs showed themselves in Western Queensland, Winton was most famous for its song. A visit to this billabong, an Outback waterhole, inspired bush poet Banjo Patterson to pen the country's most famous national tune.

That legacy lives on. Each animal being revealed to us, bone by ancient bone, is given a local nickname.

DAVID ELLIOTT: If there's a dinosaur, say, that comes from the Winton area, then it needs to have that context, and one of the strongest contexts, of course, with Winton, is Banjo Patterson, Waltzing Matilda, and, and that link.

RICHARD SMITH: Not exactly waltzing, but here's one big-boned girl: the sauropod, Matilda. Matilda stretched 60 feet, tip to tail, and stood 13 feet high at the hip. And then there's Banjo, himself, the fearsome southern hunter.

DAVID ELLIOTT: You look at these things, and they are just bitty bones, really. They don't look all that significant. But you start fleshing these bones out and putting sinews on them, putting muscles on them, and then you put that leg on that animal, as it would have stood, and you can see that what we're dealing with isn't any spring chicken. It is one hell of a big and very dangerous dinosaur. And it's not the sort of thing you'd particularly like to have chasing you up the garden path or down the hallway.

What you've got is an animal that didn't rely on its teeth to kill: massive claws, massive, big, beefed-up arms. Imagine it just getting its claws in, driving them in and just tearing them apart. And it would have had that strength.

RICHARD SMITH: In an extraordinary twist of irony, it now turns out that the spot where the bones of both Banjo and Matilda were found was indeed a billabong. It's not quite Jurassic Park, but after years languishing as a dinosaur backwater, Outback Australia is opening up as the hot new Cretaceous playground for paleontologists.

It's always been a big country out here, and after an unusually wet year, this red landscape is so green it even looks like it could carry some pretty large livestock. A 500-mile drive south of Winton brings you to the site of some of the biggest dinosaur discoveries yet, near the small town of Eromanga, population a hundred and seventy one. A warm summer's day here is 117 degrees. As far as towns go, Eromanga is no titan, but that's not so true of the bones found on nearby Plevna Downs station.

In a thundering echo of the Winton story, ranchers Robyn and Stuart Mackenzie have been unearthing bones belonging to some of the largest dinosaurs to have ever shaken the planet.

This enormous drumstick is over six feet long: a giant leg bone from an, as yet, undescribed species of Titanosaur, a big bloke called "Cooper."

ROBYN MACKENZIE (Outback Gondwana Foundation): Cooper is approximately 95-million years old, and so what we've got here is the largest bone of the largest animal that ever walked around on Australian soils and is actually up there in the top 10 in the world.

RICHARD SMITH: At over 100 tons, and with a hip height as high as the hotel roof, this giant would have barely fit in Eromanga's main street.

DR. SCOTT HOCKNULL (Queensland Museum): Australia is really in a natural history revolution. There's dinosaurs being found all over Queensland central, central Queensland from Winton down to Eromanga, and even in Southern Australia. So, in the last decade, we've found hundreds and hundreds of dinosaur bones, from the smallest dinosaurs to the largest. There's no stop to it now.

RICHARD SMITH: For a tiny town, Eromanga can make some big claims to fame: being furthest town from the sea in Australia is another one. But it wasn't always so. Ask a geologist and they'll tell you the town has lent its name to the largest inland sea in Australian history. By the middle of the Cretaceous, ocean levels were on the rise again, climbing 600 feet above today's levels. With the center of the continent already subsiding, the sea flooded into central Australia. Today Eromanga's only reliable source of water comes from underground: the Great Artesian Basin.

MAN'S VOICE: Nineteen-hundred-and-nine, it was first sunk.

RICHARD SMITH: It's one of the largest artesian basins on the planet.

QUILPIE SHIRE COUNCIL PLUMBER: It's 160 P.S.I. pressure, at a hundred degrees Celsius. You've got to be very careful working around it.

RICHARD SMITH: The heat comes from the warmth of the earth over half a mile below us. It's smelly, because it's been trapped down there for a million years.

Of course, this isn't stinky prehistoric seawater coming out, rather it's fresh groundwater that has taken an age to seep deep into the porous stone that was once the sand at the bottom of the Eromanga Sea. Without the Eromanga Sea, there wouldn't be a Great Artesian Basin. It's the fine muds of the old Eromanga sea floor that seal the top of the Artesian Basin.

Mark out the bore holes that tap into it, and you can pretty much draw a map of where the ocean used to be. About 120-million years ago, the Eromanga Sea spread out over a quarter of the continent.

I'm heading to Coober Pedy, on its southern shoreline. Scattered on the outskirts of town are strange clues to its past: petrified driftwood, the salty glint of gypsum, even rocks dropped from winter ice that once rafted overhead.

Today's mysteriously beautiful landscape was once a seascape. When the first European explorers made it out here to central Australia, some of them expected to find an inland sea. Now, we all know they failed, but not because it was a silly idea. They just got here 120-million years too late. Arrived when the tide was still in, and they would have found the Eromanga Sea full of monsters: toothy marine reptile monsters like plesiosaurs and ichthyosaurs, air-breathing animals that had returned to the sea. Both these types of reptiles are known to have hunted in Eromanga waters. And they died here, too. Sometimes a corpse sank to the sea floor and fell all the way to the future.

These days, Coober Pedy bakes in the heat. It might look like a ramshackle collection of mineshafts, underground houses and tourist traps, but this is opal central. The diggings here produce over 70 percent of the world's supply of this rainbow-hued treasure. So it's no surprise opal is Australia's national gemstone.

MINER: What you do is pull it, and you are going to go down slowly.

RICHARD SMITH: I feel like an ant here.

MINER: Yeah, don't look up too much.

RICHARD SMITH: Brothers Steve and Drago Marianovich make their living prizing these precious stones from the ancient seabed on the outskirts of town. This is their daily commute, a tight fit, dangling on a wire, 70 feet down a giant wormhole.

Wow.

Hi, Drago.

DRAGO MARIANOVICH (OPAL MINER): Hi, mate.

RICHARD SMITH: Drago has offered to lead marine reptile expert Maria Zammit and I deep into the prehistoric Eromanga sea floor. The brothers have dug an extraordinary catacomb of shafts and tunnels into a Cretaceous marine graveyard.

So, Drago, is it hard to tunnel through this?

DRAGO MARIANOVICH: Oh, yeah.

RICHARD SMITH: Opal formed here, it's thought, when silica-laden water leached through the rock, pooled where it met resistance, and then slowly evaporated. Occasionally, when this mineral-rich water encountered a fossil, a biological treasure became a mineralogical one, as well.

Wow! That is just beautiful. That green one is stunning, and it's clearly a shell.

MARIA ZAMMIT (University of Adelaide): You're absolutely right. You can really see that they are shells. I mean, that tells us a little bit about the seabed that was here at the time. However, for me, of course, the favorite are the vertebrate fossils, so, the parts of those marine reptiles that do occasionally get opalized.

RICHARD SMITH: These are some of the opalized body parts recovered, so far: backbones, rib bones, tailbones and flipper bones; near-complete skeletons from long-dead reptilian sea monsters.

MARIA ZAMMIT: I've heard of some descriptions of them being like a snake, threaded through the body of a turtle. And that's really what they look like. They've got these gigantic flippers attached to this body, and then you've got this long neck stretching out in front.

RICHARD SMITH: Enough plesiosaur remains have now been found to determine that many found in the area were juveniles.

MARIA ZAMMIT: You do see some that are only about this big. So, you know, they are obviously juveniles. How young? We don't know if they're, they're just newborn babies or if they're, they're slightly older than that, but it is suggested that, because we see so many specimens that show these signs of being quite young, that it was a nursery.

RICHARD SMITH: Plesiosaurs could calve and fatten up in the nutrient-rich waters, heading north again, before the winter returned. It might have been a safer place than most to raise a youngster, in a dangerous ocean. Sail out into the Eromanga Sea, and you would have encountered a host of strange Cretaceous sea creatures. And it's highly unlikely that they were all as friendly as dolphins.

DR. MARK NORMAN (Museum Victoria): What I think is amazing is, if this was 100-million years ago, we'd be travelling over very similar seas to this, but when we got there, we wouldn't be looking for these strange animals. They'd be looking at us.

RICHARD SMITH: Marine biologist Mark Norman and I are off to meet one of the strangest survivors from these Cretaceous seas. It's the nautilus.

CAPTAIN: Now, it should have been straight through here.

RICHARD SMITH: It's not easy to find. These days, this ancient mollusk hides away, far below the reach of daylight and divers, on the darkest, deepest reef walls in the Coral Sea. A trap has been sitting at depth overnight, set with some unusual bait.

Woo.

MARK NORMAN: They're taste for chicken went against them. The phrase "living fossil" gets used a lot for these long-lived ancient groups of animals. These went through seven mass extinctions. The dinosaurs didn't make it through one. The nautilus and their relatives over 500-million years are the great survivors.

RICHARD SMITH: Modern-day relatives of the nautilus are squids, cuttlefish and octopus, all cephalopods, a clan with a long and proud history.

Meet a face from the distant past: eyes for seeing, and hidden within a nest of 90 tentacles, a mouth for eating. Primitive it may be, but this whole prehistoric package is jet-propelled.

The distant ancestors of the modern nautilus were the nautiloids. We know them from their fossil shells, which in the early days were mostly straight.

MARK NORMAN: For hundreds of millions of years, these sorts of animals dominated our oceans and got to massive sizes. Some of the straight ones got to 10 meters long, so they were like giant telephone poles, bobbling along, hoovering up trilobites.

RICHARD SMITH: By the Cretaceous, it was the nautiloids' coiled cousins, the ammonites who ruled the molluskan world. The Eromanga Sea was full of them. Some grew larger than tractor tires, and they must have had an appetite to match. Rich pickings were to be had, throughout the Eromanga, for mollusk and reptile, alike.

Out here, even the long-necked plesiosaur needed eyes in the back of its head, for the Eromanga was the hunting ground of perhaps the greatest sea monster of all time: the pliosaur, Kronosaurus.

MARK NORMAN: So here we have just the skull of the Kronosaurus Queenslandicus, the largest marine predator of all time. We start at its snout, we go past these amazing teeth—these crushing, bone-crushing teeth—back to the back of the skull. Here is where the actual eyes would have been, and right where I'm standing, two meters away, is the back of the skull.

RICHARD SMITH: This toothy monster was a meat-eating machine, and we can even see what its last meal was.

MARK NORMAN: Right here is a ribcage of Kronosaurus. Inside its stomach we can see the vertebrae of its meal. This is a longneck plesiosaur, and it even preserves the stomach stones from this animal. On top of that, we have turtle. So this animal was eating longneck plesiosaurs and turtles.

RICHARD SMITH: These were the dying days of Gondwana. Africa had long ago slipped off to the west. Now India was gone, too. Even at the bottom of the world, the strain between Australia and Antarctica was beginning to show. Marking the boundary between the separating continents was a rift valley, rich in forests, lakes and rivers. But this entire landscape lay within the Antarctic Circle, so close to the South Pole that in the summer the sun never set and mid-winter would be dark for months on end. And that made it interesting when dinosaurs started turning up here, as well.

For over three decades, paleontologist Tom Rich has been on the hunt for bones of animals that lived in these primeval polar forests.

TOM RICH: There weren't many places anywhere in the world where you get polar dinosaurs, so that makes this site and this area particularly important. Australia was one of the most isolated blocks of land, at that time, in the world. So things we might find out about this are things we won't find anywhere else. It's almost as if this is an independent experiment in evolution, going on here.

RICHARD SMITH: Some of these experiments were small or mythopod ornithipod species, like these. Outwardly conventional, these were rare dinosaurs, thought to be permanent polar residents. Their bones lack signs of a hibernating lifestyle, suggesting they remain active right through the long chilly gloom of the sunless winter. But the dinosaurs weren't the only polar pioneers living in these dark forests. Some had fur.

While reptiles may have ruled the world, from the poles to the tropics, it's easy to forget they didn't have the planet all to themselves. There was another type of animal hiding in these prehistoric forests. They're still here, and there's one, just over there. The ancestors of the platypus have been poking their mammalian noses into the billabongs and waterways of Australia for at least 120-million years.

Proof is kept locked in this safe at the Australian Museum, in Sydney. It's another opalized national treasure: a tiny lower jaw from an ancestral platypus; a wonderful iridescent gem recovered from a lightening ridge opal mine. Warm-blooded, furry, and for the most part small, the mammals we know existed at the time could hide and hunt in the shadows of the giants. They were born survivors. It went with the territory.

Like all empires, the reign of the dinosaurs was coming to an end, and they might have seen it coming if they looked to the sky. When an asteroid slammed into Mexico's Yucatan, at the end of the Cretaceous, the repercussions were felt around the world. Though Gondwana and Australia escaped a direct hit, within an hour of impact, bits of pulverized Mexican sea floor, flung into space, began raining back down all over the planet. In places, it would have turned the sky as hot as a giant rotisserie. No good record of this bad day on Planet Earth has been found yet in the rocks of Australia. But step across to the south island of New Zealand, and you'll find hard evidence for the blanket of cosmic dust that's settled over the planet.

This, believe it or not, is the moment that the world changed forever. Now it might not look like much, but this thin gray band of rock, found around the world, offers a remarkable window into one of the most dramatic events in the planet's history. Below this boundary lie dinosaur bones, and rising in the rocks above is a world clearly recovering from a catastrophe. The days were numbered for any Australian dinosaurs that clung on after the initial impact. A tremendous darkness is brought, in the form of soot, dust and smoke, settled over the rest of the world in the immediate aftermath, lasting months, years or even decades.

Temperatures plummeted, plants withered, dinosaurs disappeared. The great lizards were gone, but the show was far from over. The tremendous calamity of the end if the Cretaceous had cleared the global stage, though this time, not only for the next scene in the great drama of life on Earth, but for the appearance of the Australia we know today.

Australia's First 4 Billion Years: Strange Creatures

PBS Airdate: May 1, 2013

RICHARD SMITH (Biologist): Over four billion years in the making, an island adrift in southern seas: it's Australia, the giant down under; a young nation with all the gifts of the modern age, but move beyond the cities and an ancient land awaits, one nearly as old as the earth itself.

Australia is a puzzle, put together in prehistoric times. And the clues that unlock the mystery can be found scattered across Australia's sunburnt face.

I'm Richard Smith, and this is an amazing country. I'll show you that every rock has a history, every creature a tale of survival against the odds. Join me on an epic journey across a mighty continent and far back in time.

Of all continents on Earth, none preserved the great saga of our planet and the evolution of life quite like this one. Nowhere else can you so simply jump in a car and travel back to the dawn of time.

In this episode: with dinosaurs dead and gone, Australia set sail for the modern world. Isolated and alone, life leaps into some unusual territory. We're uncovering lost worlds and subterranean death traps.

Blimey this tight!

An exotic band of castaways ruled this faraway land, until we turned up.

From Australia's ancient stones comes the story of our world: Australia's First 4 Billion Years: Strange Creatures, right now, on NOVA.

So far, our travels down Australia's road of time, have taken us from the very formation of the earth, through the forging of the continent, to the origin of the life and the conquest of the land.

G.P.S. VOICE: Your destination is the Present Day.

RICHARD SMITH: But it's only now, as we race towards our modern world, that the familiar face of Australia is finally revealed. This is the story of how an island continent became isolated from the rest of the world and how the life aboard this wandering ark adapted to a changing landscape. But it's a rocky road we travel. When the age of the dinosaurs came to a dead stop, 65-million years ago, a great darkness settled over the planet, and the whole course of evolution shifted.

When the skies began to clear, in the first grim days of the Paleogene, most of the great Cretaceous forests were gone. But life on Earth is tenacious. Ferns were quick to take advantage of the new world, colonizing what was left of the damaged forests of Australia, Antarctica and New Zealand. And following closely behind the ferns, a remarkable Australian tree made a dramatic comeback in the post-apocalyptic world.

This is its microscopic seed, found fossilized amongst the fern spores, just above the level of the asteroid debris that marks the last days of the dinosaurs. Like a B-grade monster, this is a tree that is hard to kill. It's the Huon pine. Every branch that falls can re-sprout from the ground. This entire tangled glade is a clone from a single, original, ancient tree.

Now, the Huon pine is more than just one of Australia's great Gondwanan survivors, this particular tree is thought to be Australia's oldest living organism.

It's been growing on this same spot—the cold wet, windy slopes of Mount Read, in Tasmania—for over 10,000 years.

But while life was on the rebound, the supercontinent Gondwana was in its death throes, and the consequences for Australia would be dramatic. India and New Zealand had already slipped away, now Antarctica and Australia were being torn apart. First, a great rift valley opened up and widened, then Australia and Antarctica started to unzip from the west. A trickle became a flood, as a new southern ocean surged into the gap between the separating lands. Only Tasmania stood firm, holding the two continents together.

Today, Tasmania wears its war wounds with pride. For over a hundred-million years, intruding molten rock had been forcing its way upwards, looking for a weak spot. This is the volcanic dolerite rock that now dominates Tasmania. There's more of this rock here than anywhere else on Earth. Towering dolerite sea cliffs guard the coast. Dolerite punches through the highlands, and the rock glowers over the capitol of Hobart, itself, all indelible evidence of the dying days of Gondwana.

This was a torrid time across the planet. Although much of the Australian landmass still lay within the Antarctic Circle, the climate was warm rather than polar, thanks to a sudden surge of greenhouse gases that peaked around 55-million years ago.

In this steamy world, the conifers that had dominated the forests of the dinosaurs were now being replaced by broad-leafed, flowering rainforest trees. Some live on, here, in Tasmania's forests. These leaves belong to a characteristic Gondwanan tree, the southern beech tree, Nothofagus. You can still find Nothofagus on the Australian mainland, in South America and even Antarctica, as fossils. They're a reminder of the days when Tasmania was holding the last of the Gondwanan brotherhood together.

At the time, you could have walked all the way from Australia, via Tasmania and Antarctica, to South America, without ever leaving the green embrace of the great Gondwanan forest. And it was through this green transantarctic highway that marsupial mammals scurried out of the forests of South America and onto Australian soil.

Marsupials, mammals with a pouch to carry their young, now dominate Australia. But marsupials were neither the first nor the only mammals in the country. They found themselves mingling with the monotremes, curious furry enigmas, like the platypus, that still laid eggs, a legacy from their distant reptilian ancestors. Only two types of monotreme live on our planet today, and they are both a little peculiar.

Now, this little guy, of course, is a truly famous Australian: the echidna or Tachyglossus, and it was, was one of the true survivors, for the early age of mammals. And we know that because it lays eggs, like the platypus.

He's tunneling to China, I think.

But there's another group of survivors from those Mesozoic times, with even closer reptilian affinities than the echidna, and they still inhabit the forests of their forbearers.

One type of feathered dinosaur did survive the great extinction. Today, we call them birds. Come eye to eye with the flightless cassowary, and the close family connection is hard to miss. While cassowaries owe their existence to the dinosaurs, the rainforests of tropical Queensland owe their existence to the birds. It's a chain of connection that links down through time, all the way to the Hewett family, modern human residents of the ancient rainforest at Cooper Creek. The cassowary has evolved to become a modern distributor of forest fruits and seeds, a job likely first done by herbivorous dinosaurs.

NEIL HEWETT (Cooper Creek Wilderness): This is the cassowary plum. The cassowary is the only animal large enough to be able to swallow this fruit whole and, in doing so, increase its germination rate from seven percent to an ultimate 92 percent.

RICHARD SMITH: In a complex relationship, with a mutual advantage, at least 37 species of rainforest tree rely on the cassowary for dispersal. It's a big job, but someone's got to do it.

Neil Hewett makes a living here, too, sharing the rich botanical heritage of his 130-million-year-old back garden with visitors like me.

NEIL HEWETT: Here in the Cooper Valley is the world's richest diversity of primitive flowering plant families found anywhere on the planet.

RICHARD SMITH: These rainforests are extremely old, far older than the Amazon, and probably the oldest continuously surviving jungle in the world. Today, they cover less than one percent of the surface of Australia.

It seems hard to believe that, for so many millions of years, most of this now-arid continent was festooned with forests of almost unimaginable richness. All that changed the moment that Tasmania finally let go of Antarctica. And with the apron strings torn asunder, sometime between 30- and 40-million years ago, Australia sailed free from the rest of the world.

When not only Australia but the Patagonian tip of South America also let go of Antarctica, cold ocean currents were able to sweep freely around the southern continent for the very first time, and Antarctica's fate was sealed. Encircled by icy currents, Antarctica and all who sailed on her began to freeze solid.

Australia, loaded to the gunnels with Gondwanan refugees, set course for the tropics: a raft of life, adrift on a sea of change.

And as it drifted, it dried. It was more than a passage into warmer climates, the freezing of Antarctica had taken much of the planet's available fresh water with it. This was the trigger for one of the planet's great biological experiments. Isolated and alone now, Australia's plants and animals began taking on their own unique identity. A remarkable rocky record of this defining moment has been found at Riversleigh, in North West Queensland.

When the fossil window reopens in the rugged limestone hills here, it opens with a bang.

For prehistoric animal hunters, like Mike Archer, Riversleigh is one of the richest caches in the continent.

MIKE ARCHER (University of New South Wales): We know nothing about Australia's mammals, right through the period when Australia separated from Antarctica at 35-million years ago, until, suddenly, the window is thrown open, and there are thousands of fascinating things to look at.

They document the last 26-million years of Australia history in exquisite detail.

RICHARD SMITH: With every fossil-rich boulder recovered, and bone, tooth and jaw released from acid bath, the ancient animals of Riversleigh are telling their own backstory of Neogene Australia. It was in the Neogene that Australia began to show its true colors.

MIKE ARCHER: The beginning of Riversleigh's story was of a rich forest, cool, temperate, permanently wet, no seasons. So we started thinking about this as a kind of a, a green cradle. Here were the first brushtail possums; here were the first ringtail possums; there were the first koalas. All the things people think about today as typically Australian animals had their roots in these ancient rainforests.

RICHARD SMITH: By the time Riversleigh's window into time was closing, around 15-million years ago, the rainforests had begun their long retreat. As the continent edged closer to the equator; the blooms of many new types of flowering plants started bursting out across the land.

Amongst them, a previously low profile, low spreading plant took root: grass. For the first time, extensive grasslands spread out across the continent, ready for the nibbling. Think Australia, and one grass-grazing animal above all others leaps to mind.

TIM FLANNERY (Macquarie University): Kangaroos are the archetypical successful mammal in Australia. They've taken over every ecological niche, from the tropical rainforests, you know, in the treetops there, through to the harshest deserts in Australia. And they do something that no other large mammal does, which is to hop.

RICHARD SMITH: Perhaps the most energy efficient means of forward motion developed by a mammal, hopping allows kangaroos to move vast distances over a tough country. The quintessential Australian they may be, but how did such a biological oddity come about?

TIM FLANNERY: If you can take the bag from me,...

RICHARD SMITH: It's a puzzle that mammalogist Tim Flannery has sought to solve since his early twenties.

TIM FLANNERY: I crawled around on my hands and knees for days on the edge of a salt lake, and I finally picked up this thing that was the size of a match head, really, it was just this tiny bone, and I knew immediately, I put it on my tongue, washed the salt off it so I could see it properly and knew that it was the ankle bone of an ancient, ancient kangaroo, far more primitive than anything that had been seen before.

RICHARD SMITH: Tim had found the missing link between the kangaroos' tree-loving, possum-like ancestors and the ground-dwelling, grass-nibbling hoppers on the country's coat of arms.

TIM FLANNERY: If you look under the microscope, here, you'll be able to see that little stepped facet there. See how it's got, like, a double step on it?

RICHARD SMITH: Oh! Absolutely, it's clear as day.

However small, the shape of this ankle bone is the key to the kangaroo story. With this stepped facet locking the bones closely together, ankle twisting was a thing of the past.

TIM FLANNERY: Kangaroos evolved from possums. Possums need to have a very flexible foot. If kangaroos had an ankle like that, they'd dislocate their ankle every time they hopped. And that stepped structure is what they evolved.

RICHARD SMITH: All of this early ankle experimentation took place in the rainforests of Australia's green cradle. And it's back in the damp jungles of North Queensland that you find the closest surviving relative of the first kangaroo. And here she is: the musky rat kangaroo, the most primitive member of the kangaroo clan and a living fossil. The first thing you'll notice about this busy little girl is the way she moves. No matter how long I sit here, watching her eat food in the forest, she'll never hop. Hopping for kangaroos came later.

Down from the trees and now with improved ankle-bone technology, the first kangaroos were set to make that giant evolutionary leap. And, in many ways, the story of their evolution charts the course of the drying out of the continent itself.

Not only new animals emerged out of this green cradle, the plants were changing too. The old Gondwanan forests shrank steadily back to the country's damp coastal corners, and in their place rose another true Australian original: the gum tree. Now, this is a tree definitely worth hugging. Meet Centurion, the tallest Eucalypt in Australia and the tallest flowering plant in the world. This towering Tasmanian mountain ash, a species of Eucalyptus, has recently been laser-measured at 327 feet high. Only a giant Californian redwood, a conifer, grows taller.

The Eucalypts have come to dominate the country. Gum trees have proven themselves in the toughest environments Australia can throw at them. They laugh off droughts and stand tall in the floods that follow. They soldier on, deep in snowfall, and respond to the perishing heat of a bush fire with a burst of new green growth. These are the trees that love a sunburnt country, and just as well.

About 5,000,000 years ago, desert began to finally claim central Australia. The last vestiges of a jungle flora, now surrounded by a sea of sand and Spinifex grass, found refuge deep in natural soaks and damp gorges. Arid Australia had arrived and so had the Quaternary, the slow drying of the continent that pushed kangaroos out of the trees and onto two legs. But as Australia drifted north, it blocked the flow of moisture to the west, as well, pushing an upright ape to stand tall on the planes of Africa.

But even more change was on its way: the ice ages. While Australia escaped the heavy ice sheets that remodeled the landscapes of the northern hemisphere, these cycles of freezing weather and glaciation sucked even more moisture from the sky. Sea levels dropped dramatically, exposing dry land from New Guinea to Tasmania. Plants grew even tougher and less nutritious. It was a climate change that pushed animals in a radical direction, best seen with a swift decent into South Australia's Naracoorte Caves.

Paleontologist Gavin Prideaux has offered to guide me to the big game of Ice Age Australia.

The ground under Naracoorte is riddled with caverns into which animals have stumbled and fallen to their deaths. As holes to the world above opened and closed, over time, snapshots of a changing land were preserved in the subterranean darkness. In 1969, a team of scientific cavers pushed on into the bowels of the earth here, further than you might think is sensible.

GAVIN PRIDEAUX (Flinders University): This is the famous squeeze.

RICHARD SMITH: So are we going through there?

GAVIN PRIDEAUX: Yes, we are going through there.

RICHARD SMITH: You're kidding me.

GAVIN PRIDEAUX: Nope. Helmet on the side as you come through the tight bit, and then just use your toes to push yourself along.

RICHARD SMITH: Some people do this for fun,…

Blimey, this is tight!

…and it probably is, if you like being the human meat in a mountain sandwich.

GAVIN PRIDEAUX: Through, Richard?

RICHARD SMITH: Oh, right, okay, okay.

Most of the mammals that entered these caves never made it out alive.

GAVIN PRIDEAUX: Well, here we are, Richard.

RICHARD SMITH: The pit of doom.

GAVIN PRIDEAUX: It certainly was.

RICHARD SMITH: When the first cavers emerged into the Victoria fossil chamber, they came face to face with a megafauna graveyard.

GAVIN PRIDEAUX: Megafauna means "giant animals," basically, big animals from the last million years or so. Animals like the diprotodon, about the size of the rhinoceros, probably weighed around two and a half tons.

RICHARD SMITH: Diprotodon, the largest marsupial that has ever lived, raised alongside the largest kangaroos of all time. Procoptodon goliath grew over two meters tall.

GAVIN PRIDEAUX: It all relates to the fact that larger animals have a much lower metabolic rate, that means they can survive on much rougher, less nutritious vegetation, becoming more and more widespread across Australia, as the country dried out.

And, of course, the carnivores, the meat-eaters, get bigger, because the herbivores get bigger.

RICHARD SMITH: This is the skull of Thylacoleo, Australia's marsupial super-carnivore. It had stealth, speed and a bite force without mammalian equal. Thylacoleo was the top mammalian predator in Ice Age Australia, but not for long. A placental mammal made land somewhere on the northern coastline. It didn't fly in, like the bats, or swim, like the rats; this mammal must have come by boat.

The first human footsteps on Australian soil were made somewhere between here in the Kimberley and Arnhem Land in the Northern Territory. The people came out of the setting sun, from Indonesia in the northwest, and they came a staggeringly long time ago. Modern science is now able to put dates on the arrival of the first people.

Geochronologist Bert Roberts uses sand grains and laser light to peer back to the start of the human story.

RICHARD "BERT" ROBERTS (University of Wollongong): We are using the very best techniques we can, at the present stage, and we now think that people got to Australia maybe 50,- or 60,000 years ago. And the very earliest occupations took place in the north of the country, maybe through Kakadu, maybe through the Kimberley.

RICHARD SMITH: Wherever those first people landed, they found themselves on a lonely alien coastline. With the oceans rising behind them and a dangerous welcoming committee, they pushed on.

TIM FLANNERY: Once you push your way through the mangroves, you would have found a world unlike anything that you'd seen. There would have been gigantic tortoises with horns like a cow.

GAVIN PRIDEAUX: So, there was a giant flightless gooselike bird, called Genyornis.

BERT ROBERTS: Huge wombats, huge kangaroos, giant echidnas, even giant koalas…

TIM FLANNERY: Sixty species of short faced kangaroos…

GAVIN PRIDEAUX: And giant goannas, about five times the size of a Komodo dragon.

RICHARD SMITH: It was a land of plenty. From the beachheads of the tropical north, it seems the first people spread rapidly south. Following the coast and tracking inland along the watercourses, they penetrated deep into the heart of the continent. Within only a few thousand years, it seems, people were camped by the shores of Lake Mungo, in far western New South Wales.

In 1969, fragments of a cremated skeleton were found weathering out of the bone-dry lakeshore. A second discovery soon followed. With dates firming it around 40,000 years, these are the oldest human remains yet found on the continent, and some of the oldest ritual burials in the world.

NICOLA STERN (La Trobe University): This is bone five.

RICHARD SMITH: The crumbling clay of the prehistoric lake edge is still releasing secrets: animal dinners, cooked on fires amongst the dunes; fragments of stone tools, relics that speak to archaeologist Nicola Stern of distant times, changed climates and a forgotten landscape.

NICOLA STERN: My interest is primarily in the rubbish left behind from people's everyday life. It's a record that spans the entire history of human settlement on the continent, about which we know very little.

RICHARD SMITH: Clues left behind in the lakeside cooking fires paint a picture of lakes brimming with water and fish, fringed with trees and wildlife: a different Mungo from today.

Mungo is a magic, moving place. You can walk on a landscape where people have been leaving footprints for over 50,000 years. There's few places on the planet with such a continual record of human occupation. Half close your eyes, and you can almost hear the sounds of the people camped on the shoreline, enjoying a sunset much like this.

There are other ghosts in this landscape. Even before the first human burials here, the giant animals of the megafauna had disappeared from the continent. The timing alone suggests human involvement, but this remains a scientific cold case, hotly debated.

Some suspect that the shifting Ice Age climate did them in, but the records stored in the bone beds of Naracoorte suggest otherwise.

GAVIN PRIDEAUX: The populations of different species of mammal waxed and waned, if you like, in response to those glacial, interglacial cycles, but nothing became extinct until about the time humans arrived.

RICHARD SMITH: Whatever it was that killed these giant animals, the final desiccating wave of global glaciation was soon making life tough for the humans that survived them. At its peak, around 20,000 years ago, the bountiful land faulted.

Forced back to the security of their lakes, Mungo people marked their passage on the edge of a drying claypan. But these first Australians left behind more than footprints. Rock shelters on the Kimberley coast hold a collection of cultural evolution extending back, it's suspected, as far as the last ice age.

With the arrival of the first people, the story of Australia is written not only in the rocks, but on them as well. Rocks polished smooth by the rub of countless human bodies, an artwork to rival any modern gallery. It's the art gallery that never closed, still cared for by the artists' living descendants, like Wunambal man, Greg Goonack.

GREG GOONACK: Welcome to Wunambal country.

RICHARD SMITH: Pleased to meet you. I'm so glad to be here; it's just so impressive.

This is a collection of artwork that archaeologist June Ross and her team are keen to fully document and date.

JUNE ROSS (University of New England, Australia): It is the story of Australia. It's a story of the people who were here first. The people that lived here, very successfully for thousands and thousands of years. And we are very interested in knowing how they managed to do that.

RICHARD SMITH: Recorded here, are clues to how people adapted to the evolving climate. At least three conspicuously different styles are on display in the caverns. The oldest are slender, elongated figures.

JUNE ROSS: They appear to be floating, almost standing on their toes, like ballet dancers. The thing that fascinates me is all the different hairstyles and headdresses.

RICHARD SMITH: This flamboyant style is then replaced by more business-like figures.

JUNE ROSS: So we think something's happening to the culture, at this particular time. We see a lot more weapons: the barbed spears, the hook sticks.

RICHARD SMITH: Whether or not dating will show this cultural shift was a response to a changing world, an evolving tropical climate certainly influenced the art of the last few thousand years.

RANGER JOHN: Gorlingi, Gorlingi. We come with respect.

RICHARD SMITH: Wanjina figures, like these images of the creator spirit Gorlingi, are strong cultural links to the modern monsoon.

Each Wet bringing new life on the land.

JUNE ROSS: When I arrived at this site for the first time, it took my breath away. And I think it has the potential to answer lots of highly significant questions, not just for Australians, but for the entire world.

RICHARD SMITH: Across the country, aboriginal Australians were witness to extraordinary change. They saw people walk to Tasmania, the last volcanic eruptions on Australian soil and, then, the coming of the Europeans.

When navigator James Cook climbed to the summit of Lizard Island, in 1770, after running aground on Endeavour Reef, he was horrified to find that his ship and crew were trapped inside a coral labyrinth, the extent of which exceeded his worst nightmares: a maze of over 3,000 reefs and islands, extending over 1,200 miles along the coast.

Australia's Great Barrier Reef is probably one of the greatest reef systems the planet has ever seen. But Cook climbed up here for salvation not scenery. He was looking for a way out.

Surprisingly, if Cook had come only about 10,000 years earlier, he wouldn't have seen the reef at all. His view from the coast to the horizon would have been of dry land, because the barrier reef hadn't arrived yet. At the height of the last ice age, sea levels plunged over 300 feet. And the older reefs were left high and dry.

Aborigines would have walked where sharks now swim, hunting kangaroos on hillsides that fish now graze. As the Ice Age waned and the world thawed, the seas rose yet again. Coral larvae drifted in to reclaim the sea floor.

Today's Great Barrier Reef, so big you can see it from space, is a surprisingly new arrival on the Australian stage. And so, for the most part, are we.

In many ways, you can think of James Cook's climb here, to the summit of Lizard Island, as a kind of turning point, the place from where our modern, still-unfolding chapter of Australia's long story began, because it's from here that he spied an escape route back to England, and the modern world soon followed.

It was like a collision of continents, a sudden end to a long isolation. In the blink of a geological eye, humans have altered the continent forever. We've cleared and cultivated the land, losing prehistoric forests and ancient soils in the process. The rest of the word has been brought in with us, in the form of animals and plants, pests and diseases, and much of what did live here has gone.

TIM FLANNERY: Well, in here, Richard, really, is the cabinet of catastrophe.

RICHARD SMITH: Look at them all.

TIM FLANNERY: This cabinet's full of mammal species that no longer exist. What we've got here is a desert rat kangaroo, last seen in 1931, central Australia.

RICHARD SMITH: Beautiful pelt.

TIM FLANNERY: Look at the beautiful, black sub-terminal bands.

These are short faced Pateros, last seen in 1875. This is a pig-footed bandicoot, last seen about 1906, in central Australia.

RICHARD SMITH: And this is the final filmed record of the now extinct thylacine, the largest marsupial predator to make it into modern times.

TIM FLANNERY: The reason it was persecuted, this animal, is because it supposedly killed sheep. We now know that 80 percent or so of the sheep that did die were stolen by convicts. They weren't killed by this animal.

RICHARD SMITH: What the film doesn't show is the moment when, in righteous indignation, the thylacine opened its remarkable marsupial jaws and bit the photographer firmly on his placental rear end.

Many of Australia's marsupials remain at risk.

TIM FLANNERY: This extinction event is equal with the one that happened 50,000 years ago of the giant megafauna. It's on the sort of scale that we see in the great prehistoric extinctions; it's the devastation of the continent.

RICHARD SMITH: As clear as the cosmic dusts marking the last days of the dinosaurs, our indelible radioactive signature is now being recorded in the rocks: the mark of the Age of Man. Around the world, we've become a powerful force of nature, the equal, at least, of any life that has come before.

You shouldn't underestimate the power of life to shape the planet. After all, it was industrious prehistoric bacteria, in the shape of stromatolites, that created Australia's vast iron ore deposits.

And it's us, life in the form of humans, that can shift whole mountains of the stuff to the other side of the world. Each year, humans shift more rock and soil than the flow of rivers and glaciers carries to the sea.

And civilization is on track to burn as much energy each year as is released as heat from within the earth. In doing all this, we alter the chemistry of our thin, precious atmosphere and finite oceans, and the geological extinction record shows we do so at our peril.

We may now hold dominion over the earth, but the planet always wins in the end. Almost nothing we see in the landscape of modern Australia will survive the test of geological time. Eventually, all this will go: the people, the buildings, probably the bedrock itself.

Today's legacies will linger in stories passed down in the rocks that are endlessly recycled and in the genes of living organisms that keep flowing down the road of time. This rhythm of life runs unbroken through the history of the Australian continent.

The first life forms skirted the shoreline here, then they climbed ashore. Now, four-and-a-half-billion years down the road, we've climbed aboard, as well.

We may not know what lies ahead for us, but thanks to some very accurate G.P.S. measurements, we do know where the continent's going. Each year now, Australia and everything on it is moving about the length of my finger, in this direction, towards the northern hemisphere. Sometime in the future, Australia should cross the equator, as it last did half-a-billion years ago. It will once again be part of another great supercontinent,a new world, somewhere in the North Pacific.

Our challenge, in this our geological instant, is to steer a path that does not cut our own future short, and with it that of the many plants and animals along for the ride.

That is what is so remarkable about the age we live in, for the first time in history there is a species on this remarkable walkabout continent that has that choice to make.