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10-Apr-2015 04:34

As Douglass matched and recorded ring patterns from trees of different ages, he confirmed that their patterns overlapped during the years the trees simultaneously lived.After establishing this basic sequence, Douglass next studied wood from trees whose dates he did not know.Much of this work focused on regions in the arid Southwest where ancient pinyon pines still live or exist as beams in old houses.In some places there, master sequences extend as far back as 8,700 years.By counting the dark ring segments, scientists can tell a tree’s age if the cross section of the trunk is complete. Based at the University of Arizona in Tucson, Douglass wanted to know how sun spot activity affected climate, and his research soon led him to pioneering tree-ring analysis.Because the width of tree rings varies with growing conditions, scientists also learn about local climate during the tree’s lifetime by comparing the rings’ different widths. For instance, higher rainfall and a longer growing season produces a wider ring than a year with low rainfall and prolonged cold. Douglass was among the first to notice that trees in a geographic area develop the same growth-ring patterns because they experience the same climatic conditions.Nonetheless, scientists find they can construct limited sequences for certain tree species in places where seasons are more pronounced or the rains less dependable.

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The calculation was straightforward: count the dark rings inward and subtract that number from the year the tree was cut.From recording tree-ring patterns in several geographic areas, scientists have found that all the region’s trees have the same pattern. He reasoned if he could trace patterns far enough back in time, he could outline a history of regional climate and see if sun spots could be related.Douglass used a bridging method to create his chronology.Another kind is the bald cypress, which grows well in wet areas like coastal swamps.Dendrochronologists make master tree-ring sequences by drawing vertical lines on a piece of paper at the end of every tree ring.

The calculation was straightforward: count the dark rings inward and subtract that number from the year the tree was cut.From recording tree-ring patterns in several geographic areas, scientists have found that all the region’s trees have the same pattern. He reasoned if he could trace patterns far enough back in time, he could outline a history of regional climate and see if sun spots could be related.Douglass used a bridging method to create his chronology.Another kind is the bald cypress, which grows well in wet areas like coastal swamps.Dendrochronologists make master tree-ring sequences by drawing vertical lines on a piece of paper at the end of every tree ring.Archaeologists sometimes study the ring patterns in beams or other pieces of wood from archaeological sites to help date the sites; they may also study the ring patterns to infer the local climatic history.