Facts about tree ring dating

Pearson and her colleagues used two different tree-ring chronologies from long-lived trees that were alive at the time of the Thera eruption but were growing 7,000 miles apart.Salzer's extensive work on long-lived bristlecone pines living in California and Nevada provided the 200 tree-ring samples representing each year from 1700 to 1500 BC."There's been a huge debate about the timing of the Thera eruption and radiocarbon versus archeological dating," Pearson said.

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"What we can say now is that the radiocarbon evidence is compatible with the archeological evidence for an eruption of Thera in the 16th century BC," Pearson said."Every tree ring is a time capsule of the radiocarbon at the year in which it grew, so we can say here's a tree ring from 1600 BC and here's how much radiocarbon is in it," she said.The radioactive carbon-14 within an annual tree ring decays at a steady rate and can act as a clock indicating when the tree grew that ring.A massive volcano such as Thera ejects so much material into the atmosphere that it cools the earth.For cold-climate trees such as Irish oaks and bristlecones, that exceptionally cold year shows up as a much narrower tree ring.

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