Coral and absolute dating

12-Dec-2014 08:30

coral and absolute dating-74

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Unfortunately, they all occur at rates that lack the universal consistency of radioactive decay.Sometimes human observation can be maintained long enough to measure present rates of change, but it is not at all certain on a priori grounds whether such rates are representative of the past.Whether in a dry Egyptian tomb or buried in wet tropical soil, a piece of obsidian seemingly has a surface that is saturated with a molecular film of water.In the American Midwest, thicknesses of gumbotil and carbonate-leached zones were measured in the glacial deposits () laid down during each of the four glacial stages.Based on a direct proportion between thickness and time, the three interglacial intervals were determined to be longer than postglacial time by factors of 3, 6, and 8.

And, if glacial time and nonglacial time are assumed approximately equal, the Pleistocene Epoch lasted about 1,000,000 years.Only one weathering is the time since the surface examined was freshly exposed.This relationship is confirmed both by laboratory experiments at 100° C (212° F) and by rim measurements on obsidian artifacts found in carbon-14 dated sequences.Practical experience indicates that the constant is almost totally dependent on temperature and that humidity is apparently of no significance.

To convert these relative factors into absolute ages required an estimate in years of the length of postglacial time.When certain evidence suggested 25,000 years to be an appropriate figure, factors became years—namely, 75,000, 150,000, and 200,000 years.