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Author Topic:   Stalagmites
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Joined: 06-23-2003

Message 3 of 6 (785022)
05-27-2016 11:02 AM
Reply to: Message 1 by vimesey
05-26-2016 10:02 AM

There's also U-Th disequilibrium dating, which works up to about 500,000 years. Thorium is insoluble in water, whereas uranium is. When uranium in the water decays to thorium the thorium precipitates out. As the thorium decays it and its daughter products approach "secular equilibrium" wherein the rates of production and destruction are equal. You can measure how far the sample is from secular equilibrium and get the date the thorium was deposited.

This was used on King Hezekiah's Tunnel in Jerusalem. Carbon dating a leaf embedded in the plaster gave a maximum age, U-Th dating of a speleothem gave the minimum age.

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