Every tree has a story to tell

From a secret location 10,000 feet high in the White Mountains of California, its thick, gnarled limbs stretch skyward. "Methuselah" is the oldest living tree found on earth. It's a 55-foot-tall bristlecone pine that's nearly 5,000 years old. It's as old as the great pyramids of Egypt. Older, by a thousand years, than Hammurabi's reign in Babylon.

Far from being a silent witness to history, Methuselah and other old trees have stories to tell. They are stories that scientists are now able to read more clearly - stories about huge volcanic eruptions, forest fires, and droughts. But trees can also tell gentler stories about log cabins, precious violins, and even three-part paintings that may have been split up long ago.

Have you ever counted a tree's rings on a stump to see how old it was? In temperate climates like that of the United States, each ring represents one year of growth. People have known this for a long time. But in the 1920s, Andrew Ellicott Douglass discovered something else about the rings: Environmental conditions (temperature, rainfall, sunlight) could help determine the width of the rings. Not only that, but patterns of wide and narrow rings could also be compared from tree to tree if the trees were the same species. Comparing younger trees to older ones, one could build a timeline of growth-ring patterns reaching back hundreds, even thousands of years. (See illustration.)

This new science of tree-ring dating was named dendrochronology (den-droh-cruh-NOL-uh-jee). The word comes from two Greek words: "dendron" (tree) and "chronos" (time).

Examining Methuselah by taking core samples using a special drill, scientists found a curious pattern. There was a series of very narrow rings. Scientists think that the rings are evidence of volcanic eruptions 3,600 years ago. The eruptions filled the atmosphere with ash and soot, enough to block the amount of sunlight reaching Earth. Temperatures fell, and the bristlecone pine grew slowly.

Many of the earth's major natural events - forest fires, century-long droughts, insect plagues, and glacial freezes - have left their marks on the world's oldest trees.

Dendrochronologists can use tree-ring patterns not only to learn about the earth's past, but also to uncover the secrets of historic objects made of wood. Abraham Lincoln's first cabin, for example, or Colonial-era houses, or the world's most famous violin.

Dendrochronologist Henri Grissino-Mayer tells how he was asked to solve a historical mystery involving Lincoln's birthplace cabin: "I was called in for a documentary being filmed called 'Lincoln: Man or Myth,' showing aspects of Lincoln's life that were debatable," Professor Grissino-Mayer says. He works in the department of geography at the University of Tennessee in Knoxville. "One was his 'birthplace cabin.' " The National Park Service had already conceded that it wasn't Lincoln's birthplace, but that's what the documentarymakers wanted to prove.

Grissino-Mayer conducted dendrochronological tests on logs from the cabin in Hodgenville, Ken., matching their tree-ring pattern to a well-researched database of ring patterns for those trees in that region.

According to the pattern of the rings, the logs had been cut down in the 1840s or 1850s. But Lincoln was born in 1809. He was a grown man when this cabin was built. Digging deeper, Park Service historians found that a promoter had built the cabin in the 1890s from logs taken from dilapidated cabins in the area. It may have been the site of Lincoln's birthplace, but it wasn't Lincoln's cabin.

The most famous violin in the world is known as the "Messiah." It is believed to have been made by the Italian violinmaker Antonio Stradivari in 1716. But the music world was rocked in 1998 when its authenticity was challenged by Stewart Pollens of New York's Metropolitan Museum of Art.

Grissino-Mayer and his colleagues carted 200 pounds of equipment - measuring tools, a special microscope, a digital camera and imaging system, and a laptop - to the Ashmolean Museum in Oxford, England, where the violin was kept.

"It was scary," Grissino-Mayer says. "The 'Messiah' violin was worth $12 million to $20 million, and they just took it out of the case and took the bridge and strings off and said, 'Here you go.' It took three of us six hours of hands-on work to study it."

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