Colter
Member
Tree rings to 11,600 years old validated:
http://asa3.org/ASA/resources/Wiens.html
The carbon-14 dates have been carefully cross-checked with non-radiometric age indicators. For example growth rings in trees, if counted carefully, are a reliable way to determine the age of a tree. Each growth ring only collects carbon from the air and nutrients during the year it is made. To calibrate carbon-14, one can analyze carbon from the center several rings of a tree, and then count the rings inward from the living portion to determine the actual age. This has been done for the "Methuselah of trees", the bristlecone pine trees, which grow very slowly and live up to 6,000 years. Scientists have extended this calibration even further. These trees grow in a very dry region near the California-Nevada border. Dead trees in this dry climate take many thousands
of years to decay. Growth ring patterns based on wet and dry years can be correlated between living and long dead trees, extending the continuous ring count back to 11,800 years ago. "Floating" records, which are not tied to the present time, exist farther back than this, but their ages are not known with absolute certainty. An effort is presently underway to bridge the gaps so as to have a reliable, continuous record significantly farther back in time. The study of tree rings and the ages they give is called "dendrochronology".
Tree rings do not provide continuous chronologies beyond 11,800 years ago because a rather abrupt change in climate took place at that time, which was the end of the last ice age. During the ice age, long-lived trees grew in different areas than they do now.
http://asa3.org/ASA/resources/Wiens.html
The carbon-14 dates have been carefully cross-checked with non-radiometric age indicators. For example growth rings in trees, if counted carefully, are a reliable way to determine the age of a tree. Each growth ring only collects carbon from the air and nutrients during the year it is made. To calibrate carbon-14, one can analyze carbon from the center several rings of a tree, and then count the rings inward from the living portion to determine the actual age. This has been done for the "Methuselah of trees", the bristlecone pine trees, which grow very slowly and live up to 6,000 years. Scientists have extended this calibration even further. These trees grow in a very dry region near the California-Nevada border. Dead trees in this dry climate take many thousands

Tree rings do not provide continuous chronologies beyond 11,800 years ago because a rather abrupt change in climate took place at that time, which was the end of the last ice age. During the ice age, long-lived trees grew in different areas than they do now.
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