Secrets Beneath the Ice

Secrets Beneath the Ice

PBS Airdate: December 28, 2010

NARRATOR: It's a mystery continent at the bottom of the world and the largest single mass of ice on Earth. For longer than humans have walked the planet, ice has dominated Antarctica.

But what about the future?

TIM NAISH (Director, Antarctic Marine Geology Research Centre, New Zealand): Ice melts from this continent, sea level goes up.

NARRATOR: As Earth gets warmer, what will happen to Antarctica?

DAVID HARWOOD (Geologist, University of Nebraska): We're going into uncertain lands, uncertain future. How will the earth respond?

NARRATOR: Today, a pioneering team is searching for answers with a bold new plan and a revolutionary new machine.

TIM NAISH: No one has ever drilled through an ice shelf, and that presents these challenges.

NARRATOR: They must drill down nearly a mile and more than 20 million years, deep into Antarctica's ancient history. In this unforgiving place, it's never been done before.

RICHARD LEVY (ANDRILL Science Management Office): It's quite amazing, when you think about where we are and what we're doing. Anything can go wrong at any minute.

NARRATOR: The stakes are high because the secret to Earth's future lies buried in Antarctica's past. Right now on Nova, Secrets Beneath the Ice.

It's the coldest, windiest, driest and most desolate landscape on the planet, with few permanent residents except penguins and seals. This frosty continent appears locked in a perpetual ice age. A colossal cloak of ice covers almost every inch of land, and in some places, the ice is so thick and so heavy it depresses the earth's crust almost half a mile.

Some people call it "Earth's freezer," but scientists call Antarctica "the ice."

RICHARD LEVY: Antarctica plays a fundamental role in the way the earth functions.

NARRATOR: For polar researchers, Antarctica is a giant laboratory, more than one and a half times the size of the United States and home to 90 percent of all the ice in the world.

RICHARD LEVY: Anything that happens down here, anything that changes, will affect the rest of the world.

ROBIN BELL (Lamont-Doherty Earth Observatory, Columbia University): Most people don't think that change in Antarctica matters to them, but when we look at New York City and we look that it's in front of the ocean, it matters.

NARRATOR: What would happen if all of Antarctica's ice were to melt?

ROBIN BELL: If Antarctica melts, sea level goes up... all of Antarctica melts, sea level goes up 12 stories in New York City.

ROB DECONTO (Climate Modeler, University of Massachusetts): Sea level would rise by more than 150 feet, flooding most of the world's coastal cities, displacing hundreds of millions of people. That would be a change that you could see from space. The earth would look different.

NARRATOR: In any case, even a loss of just 10 percent of Antarctica's ice would be catastrophic.

ROBIN BELL: It would raise the sea level over there in Manhattan about 19 feet, right up along the edge.

ROB DECONTO: Big sections of Brooklyn would be under water. Certainly the Mediterranean and some of my favorite cities, like Venice, would, would look very different.

STEPHEN PEKAR (Geologist, Queens College, City University of New York): Tens of millions of people would have to be relocated.

DAVID HARWOOD: It'd be almost a different planet.

RICHARD LEVY: If sea level changes and the climate around the coastal regions change, it's going to affect the climate where you live, it's going to affect the things you can grow, it's going to affect how you live.

There may be a list of things in store that come as a result of raising sea levels that we haven't even thought about yet.

NARRATOR: Could this be our fate? Is Antarctica heading for a major meltdown?

If so, it may happen over centuries, but it could already be starting, because the climate is changing. And it's changing because burning fossil fuels has increased the level of carbon dioxide in the atmosphere.

STEPHEN PEKAR: Today, we have something that's completely manmade. And that is the addition of carbon dioxide being put into the atmosphere by humanity, by us.

NARRATOR: Carbon dioxide is a "greenhouse" gas: it prevents the sun's heat from escaping.

STEPHEN PEKAR: I'm in the Brooklyn Botanic Garden in a greenhouse. Greenhouses, they are basically like heat motels, heat motels where the sun's rays can come in, and they get trapped inside the greenhouse. They can't get out.

NARRATOR: So, like glass in a greenhouse, gasses like carbon dioxide trap solar energy in our atmosphere. But now, those levels are increasing.

STEPHEN PEKAR: The result is that our earth is now warming up, and the ice is melting, both in Antarctica and the Arctic.

ROBIN BELL: In the north, there's two clear signals. In the Arctic Ocean, you have lots of floating ice...and sticking around through the summer. That's one sign of it getting warmer. The other sign is the edges of the Greenland ice sheet are changing.

NARRATOR: And the loss of Greenland's ice is now speeding up. In August 2010, an iceberg four times the size of Manhattan broke off the edge of Greenland. But Antarctica has nearly 10 times as much ice as Greenland, and in the past decade alone, rising temperatures have caused giant pieces of coastal ice to shrink or crumble.

Polar researchers fear that this could be just the beginning of a chain reaction. But have Antarctica's ice sheets ever collapsed before? That's what an international team of geo-detectives wants to find out.

RICHARD LEVY: We actually have some water, some melt water, coming out of the ice.

NARRATOR: To get a more precise picture of Antarctica's future, they plan to dig deep, for answers in the past, with a giant drill.

DAVID HARWOOD: By drilling into areas around Antarctica, we're able to perceive a history that has an impact for where we're headed as a planet.

NARRATOR: Antarctica was not always locked in a deep freeze. A hundred and sixty million years ago it was part of an enormous supercontinent closer to the Equator. At the time, Earth was much warmer than today, and fossil evidence suggests this giant landmass was a tropical habitat, teeming with dinosaurs. Eventually, the supercontinent broke apart and Antarctica drifted south.

As Earth was getting colder, falling carbon dioxide levels and powerful ocean currents cooled the isolated continent even further. And then, around 34 million years ago, ice slowly began to form. It would take millions of years for Antarctica to finally lock into a deep freeze, and during that time it remained warm enough for plant life to survive.

Evidence of that was recently unearthed in a relatively ice free valley in the interior. Here, geologists Alan Ashworth and Adam Lewis find a remarkable fossil.

ALLAN ASHWORTH (North Dakota State University): There's a leaf! Look at that!

ADAM LEWIS (North Dakota State University): That leaf fell into the mud maybe 20 million years ago.

ALLAN ASHWORTH: That may be the best leaf yet.

ADAM LEWIS: That's a sweet leaf.

ALLAN ASHWORTH: Yes it is. It may be the best one.

NARRATOR: And then, they find something extraordinary.

ALLAN ASHWORTH: This is like a peat moss. And then if we take, tease some of this out, they're like they're freeze-dried.

NARRATOR: Under the microscope, these brittle mosses are in pristine condition. These moss fossils are not rock, but actual plant tissue, the last vestiges of vegetation from a time when Antarctica was still warm.

They were found under a layer of volcanic ash that dates back millions of years.

ADAM LEWIS: This is the original moss tissue. And even the cells are preserved in these fossils.

NARRATOR: These plants were flash frozen when Antarctica plummeted into a deep freeze that preserved them until today.

ADAM LEWIS: It's mind-boggling. The only way is to say the climate remained very, very cold, it remained very, very dry, and it did not warm up for even relatively short periods of time in this location. Otherwise, these things are gone.

NARRATOR: But now, as Earth is heating up, what will happen to Antarctica? Will it melt, raising sea levels all over the planet? How sensitive is this frozen land to the temperature changes we currently face?

But before researchers can investigate in Antarctica, last minute testing is taking place here, over 2,000 miles away, in the countryside of New Zealand, with a brand-new drill.

ALEX PYNE (Antarctic Marine Geology Research Centre, New Zealand): Yeah. It's a shakedown. We've got a few leaking connections and things that don't quite fit as well as they need to. A little bit of modification's required…pretty common with a brand-new piece of equipment.

NARRATOR: Weighing in at a whopping 40 tons, this mechanized marvel is as heavy as a humpback whale and just as large. Towering some five stories high, the giant rig will soon dwarf everything in sight except the ice.

ALEX PYNE: This will be the largest drill rig in Antarctica that's used on land.

NARRATOR: And this mammoth rig can drill in more than one place. That's because it's mounted on a sled.

ALEX PYNE: I think it probably is unusual. All of the equipment is on sledges, so in Antarctica we pull it all with big bulldozers.

NARRATOR: It's been specially designed to drill from the ice, in order to extract hidden secrets from beneath Antarctica itself.

This unique multi-national enterprise is called ANDRILL, the Antarctic Drilling project. For team leader David Harwood, it's a dream come true.

DAVID HARWOOD: As a scientist, there's a passion that comes in trying to figure it out, trying to identify what has been the past history of the ice sheet and wondering what the future might hold.

NARRATOR: Soon, the giant drill will be dismantled and readied for a long sea voyage, but now, the ANDRILL team gathers at Christchurch, New Zealand for the six-hour flight to Antarctica in a C-17 cargo plane, jam-packed with people and gear.

Their flight passes over the Transantarctic Mountains, which divide the continent into two regions, with colossal glaciers, called ice sheets, blanketing both.

The giant east Antarctic ice sheet is ten times the size of the west. It's frozen firmly to bedrock, high above the sea, and in some places the ice towers almost three miles into the sky.

The smaller west Antarctic ice sheet is less stable. That's because it rests on land well below sea level, and it extends hundreds of miles over the ocean in floating ice shelves.

It's likely east and west Antarctica will respond very differently to a warming world.

The ANDRILL team touches down in the west, on an icy runway at McMurdo Station, the largest U.S. research base in Antarctica. As David Harwood and Richard Levy step out onto the ice, the first thing they notice is the weather.

RICHARD LEVY: Breeze is a bit chilly, but it's beautiful. It's good to be back.

NARRATOR: It's October, springtime, and it's minus-20 degrees.

RICHARD LEVY: It's the earliest I've ever been down to Antarctica, and it's very cold. When the wind picks up, it's rather an unpleasant place to be working. When the wind isn't blowing and the sun's shining, it's actually really quite nice, but very cold.

NARRATOR: But even a sunny afternoon can turn nasty at a moment's notice.

Guy in shorts: It's a beautiful day!

NARRATOR: McMurdo Station has been a vital hub of research for over half a century. What began as a tiny outpost has, over the years, grown into a small town. McMurdo houses a population of 200 people year-round, but during the research season, it becomes home base for over a thousand.

Every year, McMurdo supports scores of research projects, providing lab facilities, food and supplies, and survival training for teams of scientists who will head out to remote field camps. This season, those numbers include the ANDRILL team of over 50 technicians and researchers from the U.S, New Zealand, Germany and Italy.

ANDRILL is funded by their governments and the National Science Foundation.

RICHARD LEVY: There's probably a week, at least, of work in McMurdo, where we have to get all of our gear sorted out, getting everything we need in order to be able to work and survive out in the field.

NARRATOR: As they gather supplies for more than a month on the ice, one item is in high demand.

LAURA LACY (ANDRILL, University of Nebraska): Sugar actually heats your body. It gives you quick energy, especially if you're, like, freezing. And we expect to be very cold.

We don't really know how much chocolate is enough. We can take up to 560 candy bars. But I‘m looking at this, and I'm already getting queasy. I don't know if I can eat this or not.

TIM NAISH: Hey, David.

NARRATOR: As ANDRILL researchers prepare for life in the field, they join hundreds of other scientists fanning out across Antarctica. And many are focused on the same question: could Antarctica be headed for a meltdown?

ADAM LEWIS: Over here is Mt. Boreas.

DAVID HARWOOD: We're going to have a lot of scientists working together and challenging each other's theories, challenging what we know. As a community, we're going to find the answers.

NARRATOR: But the continent won't give up its secrets easily. The stark beauty of Antarctica masks a treacherous nature. More than 70 percent of all the fresh water in the world is harbored here, but most of that water is frozen. And with less precipitation than the Sahara, Antarctica is the driest desert on Earth.

Raging winds, of up to 200 miles per hour, sometimes blast the frozen terrain, where temperatures can drop to a hundred degrees below zero. Only during the short Antarctic summer can most researchers gather precious scientific data from this giant mystery continent.

A four-hour flight and 400 miles from McMurdo, is the center of the west Antarctic ice sheet, and for one team, this is the best way to find out about the past.

KENDRICK TAYLOR (Desert Research Institute): This is the side of a snow pit. It's a thin wall between two pits. The other side is open, so the light can shine through the wall. You can really see the different layers in the pit. So this is one year's worth of snow accumulation, and there's a second year's worth of snow accumulation here, below it: two years of record, right here in the snow pit. But, of course, we want to go back a lot further in time than that. In order to do that, we can't just use shovels and chain saws like we did here, so we have to use a drill.

NARRATOR: Ken Taylor's team is drilling through ice. Their goal is to gather samples from the nearly two-mile-thick west Antarctic ice sheet. And the deeper they go, the farther back in time they travel.

REBECCA ANDERSON(Desert Research Institute )We're at about 480-meters deep right now. This was right around the time when Jesus lived. It's right about zero A.D., right when B.C. years turned into A.D. years.

NARRATOR: These ice cores contain tiny bubbles of ancient atmosphere that were trapped each year as the snow was compressed into ice.

KEN TAYLOR: Nice bubbles in this one. That's ancient air in there. When we crush samples like this, that'll get the gas out of there. We can sample the ancient atmosphere. We can also get a record of how things like temperature and sea ice changed in the past. And by combining these different records, we can understand how the climate system has operated in the past.

NARRATOR: But the ice record, valuable as it is, only goes back about 800,000 years, a tiny fraction of geologic time. To get a more complete picture of Antarctica's climate history, you have to drill farther back in time.

And that's what the ANDRILL team is trying to do. They want to paint a picture of Antarctica as it changed from warm to cold, millions of years ago. In order to do that, ANDRILL will have to drill deep into the earth. But finding the right location is a major challenge on a continent covered by ice. And even in those few places where the ice has receded, it's still not easy.

ANDRILL's David Harwood and Richard Levy are searching for places to drill. But as they fly over a field of rubble, they see that gathering evidence for a chronological history is not possible here. Something has stirred things up. And that something is the ice itself.

That's because ice moves. For tens of millions of years, glaciers have slowly scoured the land, gobbling up rocks and debris and spreading them all across the landscape in random order.

DAVID HARWOOD: This we call "glacial paleontology," some call it "garbage pile paleontology" ‘cause we are looking and sorting through these moraines to try and get pieces of information that the ice sheet has brought to us.

NARRATOR: A moraine is the chaotic accumulation of rocks and debris deposited by glacial movement.

RICHARD LEVY: This one, here, has an abundance of shell fossils.

NARRATOR: This shell, brought here by a glacier, comes from a time when the continent was warmer and water ran through these valleys.

This landscape is a treasure trove of Antarctica's climate history, but the ice has scrambled all the clues.

DAVID HARWOOD: We're looking at a jigsaw puzzle.

NARRATOR: Yet there's one place where the evidence remains undisturbed, intact. That's in the sea floor beneath the Antarctic ice shelf, where the glacial movement has also deposited layer after layer, in chronological order.

DAVID HARWOOD: Drilling gives us an opportunity to get a, get a serial history in time, back in time. Each layer goes back in time. We know a rock above is younger than a rock below, so we can put it into a history.

NARRATOR: The ANDRILL team aims to drill through the Antarctic ice and the sea below. Then, like a hollow tube thrust through a layer cake, they'll bore deep into the ocean floor, in order to recover millions of years of rock and mud that trace Antarctica's climate history.

Even after ice began to form in Antarctica, around 34 million years ago, the continent remained warm enough for plant life to survive, a lot like areas of New Zealand, today, where ice can be found bordered by trees and plants.

But when did Antarctica plunge into a solid deep freeze? And how did it happen? Was it gradual or abrupt? Will the story of how Antarctica changed from greenhouse to icehouse reveal new clues about the continent's climate future and our own?

The ANDRILL team will spend the next few weeks searching for drilling locations from the surface of the ice, but David Harwood remains focused on what lies below.

DAVID HARWOOD: When I'm driving across there, I'm always thinking about what's beneath us. I'm over about 15 feet of ice, and over that, I'm over about 1,500 feet of water, and the sediment's below that.

NARRATOR: Here, at the bottom of the world, the sun never sets in the summer, and as night blends into day, the work begins in earnest.

The team heads out to McMurdo Sound, a place where the ocean freezes annually, creating a precarious platform of floating sea ice that will only last a few months.

DAVID HARWOOD: We're standing, right now, in the southern part of McMurdo Sound. Seasonally, this region will break out to sea ice that we're standing on and will melt out. It's now strong enough, perhaps 20 feet beneath us is the thickness of ice, and then 1,500 feet of water beneath us, as well.

NARRATOR: Just to be sure they're in the right place, the team blasts powerful sound waves through the sea ice and into the seafloor below. The result is a sonic street map of layer after layer of rock and mud, each one representing a different era of the past.

DAVID HARWOOD: By looking in the past, we can maybe project into the future. How dynamic has been the behavior of the ice sheets. Have they been static and slowly changing? How active of a player have they been?

NARRATOR: Finally, it's time to tow the giant drill out onto the ice. To ensure that the weight of the rig isn't supported by the sea ice alone, divers attach flotation devices to the drill pipe. And at the end of that pipe is a whirling tool with a unique cutting edge, a drill bit made of diamonds, that can bore through almost everything in its path.

DAVID HARWOOD: The diamond core system that we have, it's almost like melting the core down through the rocks, just cuts through whatever's there. If you hit a big boulder, you'll just end up with a cylinder of that boulder, and it'll just keep going.

NARRATOR: Now the real drilling begins. There's not a minute to waste, because the Antarctic research season is so short. The crews work around the clock to recover cores of rock that trace Antarctica's ancient past.

The powerful drill bores down over three quarters of a mile, bringing up 12 feet of core at a time, each foot averaging a thousand years of climate history.

It's an astonishing feat.

RICHARD LEVY: It's quite amazing, when you think about where we are and what we're doing. We've got a drill rig, a 60-ton to 90-ton—with all the equipment on it—the drill rig, sitting behind us, on eight meters of sea ice, above 380 meters of water. And then we're drilling down into the seafloor below that with a 3 to 4 inch diameter pipe that's turning round and around like a piece of spaghetti hanging down through the water and into the ground. And it's wobbling around a bit, and we're turning around and bringing out core from deep from within the earth.

Anything can go wrong at any minute with this process.

NARRATOR: And all too soon, it does.

Sometimes even a drill bit made of diamonds can run into trouble.

ALEX PYNE: We haven't been getting particularly good quality core. And we're suspecting that the drill bit has been damaged. In places it's a little bit narrower than it should be for the size of the diamond bit. And that means we have to pull all of our pipe out—about 17,000 meters—and replace the bit and then put the pipe back down the hole. And that's going to take us about 24 hours to 36 hours.

NARRATOR: Removing and replacing nearly a mile of pipe is no easy task, especially when it's your job to change it all out, piece by piece. But for other members of the ANDRILL team, it's a welcome break.

MICHELLE BRAND-BUCHANAN: Suppertime! Come and get it!

NARRATOR: In an extreme environment like Antarctica, nobody's on a diet. Your body is working so hard to stay warm, packing away 6,000 calories or more a day is not an indulgence, it's a necessity. And because Antarctica is drier than the hottest desert, dehydration is a constant concern.

And keeping the drill up and running is another. Finally, after a day and a half of hard work, the new bit is in place and drilling is back on track.

They recover a 12-foot length of core. Wrapped in a protective cover, workers carefully carry it back to the lab to be examined.

When they crack it open, it's in perfect condition. This mud and rock is more valuable than gold, because each core is a time machine.

DAVID HARWOOD: We're currently down at a depth of about 440 meters.

NARRATOR: That's about a quarter mile down, corresponding to a time, at least 15 million years ago, when Antarctica was still warm.

As the cores are recovered, each section is sliced lengthwise, X-rayed and scanned in labs at the drill site and back at McMurdo.

MATT CURREN (Curator, Antarctic Marine Geology Research Facility): These cores came out of the ground three days ago; they were split yesterday; they were imaged yesterday. The sedimentologists worked the nightshift, 12 hours, describing these cores millimeter by millimeter, looking at the color, size ratios, any kind of structure they see in a core, trying to understand how these sediments were deposited.

NARRATOR: Each core tells a story, depending on its texture, color and contents, and some of those stories are spectacular.

DAVID HARWOOD: We're seeing some macrofossils, some large shells.

NARRATOR: These shells are evidence of warmer times, even as Antarctica is icing up.

MARCO TAVIANI (Institute of Marine Science, Italy): This is one of…the most spectacular fossil found was in ANDRILL this season. This is a scallop. This kind of scallop simply do not live in extreme polar waters.

NARRATOR: And there are other clues, some of them nearly invisible. Hidden inside these cores are shells of microscopic algae called diatoms. For ANDRILL climate detectives, these tiny diatoms create a highly revealing picture of the past, because not all diatoms are alike. Some species are adapted to colder conditions, while others flourish in warmer waters.

DAVID HARWOOD: We use them as biological markers, to be an index of different environmental conditions: cold or warm, frozen waters or open ocean waters.

NARRATOR: Again, the ANDRILL team examines the cores from around 15-million years ago. They find smooth green sands, containing diatoms that thrived in relatively warm water, confirming this was a time before Antarctica finally froze over.

DAVID HARWOOD: This is a very well defined warm period, iceberg-free waters, open waters where diatoms are growing and thriving. You can see this persisted for quite some time.

NARRATOR: A picture is beginning to form of a long period of transition, starting 34-million years ago, when a cooling climate led to the formation of ice. But even so, conditions remained relatively mild.

But when did Antarctica finally slip into a deep freeze? The answer lies in cores from around 14-million years ago. Instead of smooth and green, these cores are rocky and gray, and some contain diatoms that thrived in cold glacial waters.

This amazing discovery reveals a rapid change from cool to frozen. It fills in what has always been a blank page in Antarctica's climate history.

Next season, they'll attack another crucial question: after Antarctica froze 14-million years ago, did the ice ever melt or has it remained a frozen wilderness right up until today?

That answer will have to wait. Cracks in the sea ice tell the team it's time to return to base.

CECE MORTENSON (Raytheon Polar Services): We've seen the ice breaking quite a bit in the last month, but it's not broken in any further south than it is right now.

RICHARD LEVY: We can only be on this site for so long before the sea ice starts to melt, before the conditions change and, for safety reasons, we have to get off the sea ice.

NARRATOR: The precarious sea ice of west Antarctica may come and go with the seasons, but what about the giant east Antarctic ice sheet? A mountain of ice so high, it covers mountains.

ROBIN BELL: This is like an M.R.I. of the ice sheet. Some places it's really thick, two miles thick and pretty flat and boring. But then there are other places where what we discovered were hidden mountain ranges the size of the Appalachians, but totally hidden by the huge east Antarctic ice sheet.

NARRATOR: There's 10 times as much as ice in the east as in the west, but a small portion of the east has almost no ice at all. It's an unearthly location that defies the very image of Antarctica. These are the dry valleys: cold, barren, and except for a few scientists, almost completely devoid of life. The landscape is so alien that NASA has used it as a test site for space programs.

DAVE MARCHANT (Glaciologist, Boston University): It's a fantastic place. You can't find this anywhere else on Earth. Its closest analog is the surface of Mars.

NARRATOR: Mullins Valley is the ultimate remote field camp. It serves as home base for a pioneering band of glaciologists, led by Dave Marchant.

Marchant and his team are conducting research the rugged, old-fashioned way. They'll live in tents and won't be picked up for two months. They need to be self-sufficient, and for the most part, they like it that way.

MAN: Burritos!

DAVE MARCHANT: You come out here, you have no contact with the outside world—no email, no real telephone contacts—so you can totally immerse yourself in the science, and that allows you to think 24 hours a day about what you're doing. The other side of that is, is that you have no idea what's going on outside.

LAURA ROBINSON (Woods Hole Oceanographic Institute): At the beginning of the season, I didn't like it when you would freeze and the frost would form on the outside of the sleeping bag, but it's warmed up now, and it's a little bit more comfortable in the morning.

DAVE MARCHANT: Small setups like we have, which are helicopter-supported, are isolated. They're among the most isolated in the region, and as a result, we have to check in daily with McMurdo.

I'm trying to heat the batteries up so we can get a signal out. Right now there appears to be no satellite covers and the batteries are a little bit cold, so I'm trying to warm it up. Sometimes, you have to contort your body in various ways to get the signal. Nah, we don't have enough signal yet.

Here we go. We got something that might work.

Mac ops this is Gulf 054 Mullins Valley. We have all seven on board, and all is well. Over. Ugh… lost transmission.

This valley holds an incredible record. This area is so dry and so cold, that the landscape is pristine. The rocks we see here are millions of years old.

NARRATOR: Marchant believes that little has changed here for millions of years.

DAVE MARCHANT: What, to me, is exciting is that we're walking on an ancient landscape. Imagine living 10 million years ago, and if you were in Antarctica, this is what you'd see, exactly as it is today, hardly modified at all.

NARRATOR: But when Marchant's team drilled beneath this rubble, they found something totally unexpected: a hidden glacier that extends hundreds of feet below the surface.

DAVE MARCHANT: This is, in my opinion, the oldest dated buried glacier on Earth.

NARRATOR: The evidence comes from volcanic ash. The dry valleys are surrounded by extinct volcanoes that erupted millions of years ago.

DAVE MARCHANT: We're finding ash deposits on top of the ice. The ash dates are coming back as old as 8,000,000 years.

NARRATOR: And, according to Marchant, this volcanic ash shows that this hidden glacier, once frozen, has never melted.

DAVE MARCHANT: This volcanic ash that erupted from a volcano and has been sitting here for millions of years, it shows no chemical alteration, which you'd expect if there were any amount of liquid melt water over that duration. The fact that it's dry and pristine tells me it's always been here, which is incredible.

NARRATOR: Equally astonishing, and just 300 miles away, there appears to be a completely different picture.

Exploring east Antarctica, closer to the South Pole, ANDRILL's David Harwood found leaf fossils and pieces of wood. Surprisingly, according to Harwood, these date to a relatively recent time, when Antarctica was not only warmer than today, there were plants and trees.

DAVID HARWOOD: This is a piece of southern beech. This wood is not fossilized, in the sense that it's petrified. It could still burn. To find the wood and leaves together, it is pretty phenomenal. It's really phenomenal for Antarctica, for, particularly for Antarctica in this time period, about 4,000,000 years ago.

NARRATOR: This season, the drill is set up to find evidence of what happened in Antarctica during this period, 3- to 5,000,000 years ago. It's a time known as the Pliocene.

ROB DECONTO: Now, what's important about that is that the Pliocene was globally warmer than today.

NARRATOR: The same temperatures as our Earth may be headed for at the end of the century, if climate change predictions are correct.

TIM NAISH: If we go back 3- to 5,000,000 years into the geological past, we know that there was a time when Earth's climate was warmer than it is today, perhaps by three to four degrees. So, it's the best example we have of where the climate's heading in the next hundred years.

NARRATOR: The drill's new location is on the giant Ross Ice Shelf, which extends out and over the ocean. It's the largest ice shelf in the world, and it helps hold back the massive Antarctic ice sheet from flowing into the sea.

ROB DECONTO: These ice shelves are very important, because what they do is hold back the flow of ice that's actually trying to flow out into the ocean. We call that buttressing.

NARRATOR: If warming oceans cause the Ross Ice Shelf to break up and melt into the sea, the west Antarctic ice sheet would eventually follow right behind.

The ANDRILL team is looking for the answer to a critical question: when Earth was warming during the Pliocene, what happened to the ice? Did the Ross Ice Shelf melt, taking the giant ice sheets with it?

Drilling on an ice shelf brings with it a unique set of technological challenges, including constant problems with mud and water.

Unlike drilling through sea ice, which is just 26 feet thick, the ice shelf here is 400 feet.

ALEX PYNE: We're looking at at least doubling or trying to double our capability below the seafloor and penetrate to a thousand meters or better into the seafloor.

NARRATOR: But that's only the beginning.

TIM NAISH: No one has ever drilled through an ice shelf, and that presents these challenges. The ice shelves, they float up and down with the tide, so you've got to deal with a vertical elevation change. They move sideways, they ‘flow,' so, eventually, your drill pipe is going to get bent.

NARRATOR: Can the drill bore through a thick layer of ice that's constantly moving, without breaking or getting yanked out of the seafloor?

To confront this unique challenge head-on, the ANDRILL team invents a new tool, a hot-water drill. This marvel of engineering is a moving ring of heat that blasts jets of steaming water to melt a wide hole so the drill can operate freely through 400 feet of shifting ice.

And once again, time is so precious the team must work around the clock, not only retrieving cores, but also analyzing them.

It's 2 a.m., but you wouldn't know it. Geologists are busy logging cores like it's early afternoon.

MATT CURREN: We're laying out the cores in the proper sequence, from top—the very highest point in the core—all the way to the very lowest point of the core, here.

NARRATOR: An 80-foot core that dates back about three million years is closely examined. It contains microfossils of single-celled animals known as "forams." They're from the crucial warm period called the Pliocene, and these tiny shells are precise indicators of ocean temperature.

GAVIN DUNBAR (Antarctic Marine Geology Research Centre, New Zealand): So, these guys are the size of a grain of sand. Because the same species has lived through time, we can use the chemistry of modern examples to allow us to calibrate, if you like, the chemistry of ancient examples.

TIM NAISH: What Gav's doing here is he is measuring the amount of two metals, magnesium and calcium, that are in the ocean and get incorporated into the shell of the foram when it's growing in the ocean. And that process is dependent on the temperature of the ocean. So, we know the magnesium, we know the calcium, we can determine the temperature of the ocean at the time that foram lived.

NARRATOR: And because of that, ANDRILL researchers can now calculate Antarctic water temperatures during the Pliocene.

TIM NAISH: What this is telling us is that temperatures were three to four, perhaps five degrees above present.

ROB DECONTO: Even just one degree rise in ocean temperatures in the waters surrounding Antarctica will attack and begin to melt the ice shelves from below, very quickly.

The air temperatures will stay cold enough to keep things frozen at the surface, but what we're worried about is the ice being attacked from beneath, not from above.

NARRATOR: And the cores reveal this is what happened during the Pliocene, when global climate was warming. But they display even more change than expected, revealing not only a patchwork of glacial rubble, but also smooth mud from open seas, indicating that ice both froze and then melted many times.

ROSS POWELL: There's a really important change right here. This interval shows us quite a dramatic change in the environment. There was ice and there was no ice.

GREG BROWN (Institute of Geological and Nuclear Sciences, New Zealand): The ice sheet has gone backwards and forwards; it's advanced and it's retreated.

NARRATOR: As they examine core after core from the Pliocene, they continue to see surprising signs of change.

TIM NAISH: The results of the drilling are simply spectacular. They give us a picture of a dynamic ice sheet coming and going regularly, more than 60 times.

What we're seeing in this record is telling us that Antarctica is not just a benign spectator, it's a player.

NARRATOR: What this means is while it was generally warm during the Pliocene, there were also brief periods of cooling. And the ice was exquisitely sensitive to even small changes in climate. Just a few degrees could tip the scale from ice to no ice.

So, what's in store for our future? As Earth continues to warm, how much Antarctic ice will melt, and how high will sea levels rise?

The ANDRILL scientists turn to computer models by Rob DeConto and Dave Pollard.

ROB DECONTO: We developed these climate models based on our best understanding of the physics of the climate system and, in this case, ice sheets.

NARRATOR: And now, information from ANDRILL is added to the climate model.

ROB DECONTO: This is a computer model simulation of the Antarctic ice sheet over the last several million years and covers a good chunk of the interval that was recovered by the ANDRILL sediment core. So, we're looking for the same kind of behavior in our models that we're seeing in the geological record.

NARRATOR: As the model simulates the warming periods of the Pliocene, all of the ice shelves disappear, followed by the entire west Antarctic ice sheet and edges of the east. And as temperatures change, the ice refreezes and melts again and again.

ROB DECONTO: And that's important because the changes in the ice sheet that we're seeing here reflect pretty significant changes in sea level.

NARRATOR: According to DeConto's model, sea levels rose about 23 feet during the Pliocene. Temperatures back then were three to five degrees higher than now, just what's projected to take place by the end of the century, but there's a lag time in the way ice responds that may delay the impact for hundreds if not thousands of years.

Regardless, coastal cities all over the world would be at risk, potentially displacing millions.

ROB DECONTO: We would be remapping places like Boston and New York and the Bay Area. Not to mention, of course, places like Louisiana, Miami, New Orleans, of course.

NARRATOR: But even that might not be the worst-case scenario.

TIM NAISH: Things were very similar to today in terms of our climate.

NARRATOR: Tim Naish brings Rob DeConto to New Zealand to look at a possibility that's even more frightening.

ROB DECONTO: This is the first time I've seen the actual direct evidence for what the models are doing.

TIM NAISH: We're seeing a deepening sea level rise, up through here.

We're going to look at some rocks that are the same age as rocks withdrawn in Antarctica that give us the record of global sea level changes.

NARRATOR: Here, along the Rangatikei River, tectonic forces have raised the land, and the river has cut into the earth, to expose layer after layer of sediment that once was the seafloor.

What they find are shells dated to the warming era of the Pliocene. These shells provide a way to chart sea level in the past, because some of these species still exist today.

TIM NAISH: Many of these shells you see in here actually live today. So they live around the coastline, and we know the water depth they live in today. So, by breaking them out of these rocks and identifying them, we can say the depth they were living over 3,000,000 years ago here.

NARRATOR: Because these shellfish live on the seafloor and can only survive in water at specific depths, they suggest that sea levels in the Pliocene were much higher than even the computer models predict.

TIM NAISH: This is really it, Rob. This is where we would say we have the evidence for global sea level being up to as much as 20 meters above present.

NARRATOR: That's over 60 feet! In order for sea level to have risen that high, an enormous amount of ice must have melted. And this raises a startling possibility: that a large part of the vast east Antarctic ice sheet melted along with the west. And if it melted once, could it melt again?

ROB DECONTO: That could be a very bad thing, because that would actually produce a contribution to future sea level change that we really haven't been thinking about.

NARRATOR: This presents an even more dangerous and unpredictable picture of Antarctica.

ROBIN BELL: What's been surprising is even geologists thought that glaciers and ice sheets were these large static features, which we would never really see change in our lifetime, but glacial processes are no longer quite as glacial. Things are moving faster than we had thought.

NARRATOR: What's driving these changes are rising levels of greenhouse gases.

ROB DECONTO: In the next five years, greenhouse gas levels will be like they were in the Pliocene. But we're not just going back to the Pliocene. Some of the projections put CO₂ levels at twice the concentrations of the Pliocene by the end of the next century. We're essentially going back to the time of the dinosaurs, when there was very little ice on the planet and there were forests covering Antarctica.

NARRATOR: And signs of change are already here.

Scientists were completely caught by surprise when, in 2002, the Larsen Ice Shelf shattered apart, without warning, in just a few weeks.

And today, the Wilkins Ice Shelf, a block of ice approximately the size of Connecticut, barely hangs on.

DAVID HARWOOD: I would say it's, it's inevitable that west Antarctica will disappear. How long it will take east Antarctica to engage is something that's, that's not yet known.

NARRATOR: In the coming years, the ANDRILL team will continue to explore Antarctica's climate history, in order to gain valuable insight into Earth's future.

With each new core, we gain new knowledge about a continent that's always been shrouded in mystery. But its fate remains very much tied to our own.