dating tree rings

Nancy Salas, 38 years old


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Pando Latin for "I spread out" , also known as the trembling giant , [1] [2] is a clonal colony of an individual male quaking aspen Populus tremuloides determined to be a single living organism by identical genetic markers [3] and assumed to have one massive underground root system. Pando is currently thought to be dying. Though the exact reasons are not known, it is thought to be a combination of factors including drought , grazing , and fire suppression. A study published in October concludes that Pando has not been growing for the past 30—40 years. Human interference was named as the primary cause, with the study specifically citing people allowing cattle and deer populations to thrive, their grazing resulting in fewer saplings and dying trees. Pando is thought to have grown for much of its lifetime under ideal circumstances:

There are many carbon atoms in our environment. The vast majority of these are 12 C pronounced "c twelve"the stable isotope of carbon. However, cosmic radiation constantly collides with atoms in the upper atmosphere. Part of the result of these collisions is the production of radiocarbon 14 C, pronounced "c fourteen" dating tree rings, carbon atoms which are chemically the same as stable carbon, but have two extra neutrons. Radiocarbon is not stable; over time radiocarbon atoms decay into nitrogen atoms. This tendency to decay, called radioactivity, is what gives radiocarbon the name radio carbon. The atmosphere contains many stable carbon atoms and relatively few radiocarbon atoms.

Dendrochronology or tree-ring dating is the scientific method of dating tree rings also called growth rings to the exact year they were formed. As well as dating them this can give data for dendroclimatology , the study of climate and atmospheric conditions during different periods in history from wood. Dendrochronology is useful for determining the precise age of samples, especially those that are too recent for radiocarbon dating , which always produces a range rather than an exact date, to be very accurate.
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About two miles high, in the White Mountains of eastern California, grows a unique tree, Pinus aristata also referred to as Pinus longaeva. The Bristlecone pine became famous in scientific circles through the work of Dr. Edmund Schulman of the University of Arizona. His dendrochronological studies spanned almost thirty years, of which the last five were spent mostly in the White Mountains. So far, this amazing record from the Bristlecone pines only applies to the southwestern portion of the United States and has become useful also to the field of archaeology where ancient roof beams have been more accurately dated using the tree-ring growth records. The White Mountains rise abruptly east of the Sierra Nevadas, reaching over 14, feet in elevation near the ancient Bristlecone pine forest. They lie in the rain shadow of the Sierras, with an average annual rainfall of inches. Bristlecones grow in other similar areas and were already the focus of much speculation when Schulman arrived on the scene in

Ron Towner from the Laboratory of Tree-Ring Research at the University of Arizona explains the principles behind dendrochronology and why this dating method is valuable to archaeologists. Ron demonstrates how to accurately count tree-rings, and discusses the importance of patterns and master chronologies. Trees are often used to make analogies about the past. Family trees, the tree of life, getting back to your roots…. But beyond the powerful imagery that trees give us to represent our history, what can trees actually tell us about the past? Dendrochronology is the scientific method of tree-ring dating. Americans first developed it in the early 20th century and now "dendro" is a common method of chronology that is used by scientists all over the world.

The science of constructing chronologies from tree rings is called dendrochronology. The basic concepts involved are not complex. Modern trees are known to produce one growth ring per year. This is a result of the annual cycle of seasons.