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by Rick Groleau If you're the skeptical type, you might raise an eyebrow when you hear that a particular Viking ship was built in the year 819. How could anyone determine the age of such an aged object so precisely, especially when there are absolutely no records to verify the date? Well, tree-ring dating, or dendrochronology, can be this precise, and even more so. Dendrochronologists showed that an ancient wooden road uncovered in southwestern England not only was built in 3806 B.C., but that the trees used for the road were chopped down in the winter of that year (the winter of 3807-3806). The science can also reveal the origin of old pieces of wood. In one case, archeologists determined not only the age of a Viking ship found in Denmark, they also learned that it was built in Ireland.
Every year a new ring of growth is added to a tree's trunk and branches, just beneath the bark. The thickness of this ring depends on how much the tree grows during the year: favorable growing conditions result in a fat ring, unfavorable conditions, in a narrow ring. And because trees in a given area generally experience the same growing conditions, those trees have similar tree-ring patterns. By starting with a living tree and working back, using wooden objects of different ages, dendrochronologists have created continuous chains of tree rings that stretch back hundreds, sometimes even thousands, of years. They then use these tree-ring chronologies to date wooden objects, to determine a general area in which the wood grew, to find out about past climates, and more. This Hot Science lets you assemble your own tree-ring chronology. You'll start with a tree-ring sample from a living tree and, using other samples, piece together a pattern of rings that stretches back through time. Build a Tree-Ring Timeline requires the Shockwave plug-in Anatomy of a Tree Ring Growth and Sensitivity Skeleton Plots Explore a Viking Village | Who Were the Vikings? Secrets of Norse Ships | The Viking Diaspora Write Your Name in Runes | Build a Tree-Ring Timeline Resources | Transcript | Site Map | The Vikings Home Editor's Picks | Previous Sites | Join Us/E-mail | TV/Web Schedule About NOVA | Teachers | Site Map | Shop | Jobs | Search | To print PBS Online | NOVA Online | WGBH © | Updated November 2000 |
Go to Build a Tree-Ring Timeline
Tree rings can reveal more than just a tree's age.