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In all three lakes, rates calculated from Pb distributions both above and below this horizon agreed, within measurement uncertainty, in recent and older cores.Furthermore, when the older data were corrected for 20 yrs of burial, the changes in slope in Pb distributions occurred at the same depth in each pair of cores.This study provides one test of that possibility by comparing recent measurements of Cs dating is used to confirm sediment accumulation rates in the recent cores.In the three Connecticut, USA, lakes studied, sediment accumulation rates changed abruptly to higher values between 40-50 yrs ago (increasing by factors of 2.2, 2.9, and 3.0).The calcium-potassium age method is seldom used, however, because of the great abundance of nonradiogenic calcium in minerals or rocks, which masks the presence of radiogenic calcium.On the other hand, the abundance of argon in the Earth is relatively small because of its escape to the atmosphere during processes associated with volcanism.Pb has been used for more than two decades to provide the geochronology of annually deposited sediments and to construct pollution histories.
For two of the three lakes, there was a significant difference in average sediment accumulation rate during the past 33 yrs as calculated from Pb in the recent cores.
Join Britannica's Publishing Partner Program and our community of experts to gain a global audience for your work! This dating method is based upon the decay of radioactive potassium-40 to radioactive argon-40 in minerals and rocks; potassium-40 also decays to calcium-40.
Thus, the ratio of argon-40 and potassium-40 and radiogenic calcium-40 to potassium-40 in a mineral or rock is a measure of the age of the sample.
The selected size fraction is cleaned in ultrasound and acid baths, then gently oven-dried.
The target mineral is separated using heavy liquids, then hand-picked under the microscope for the purest possible sample.
Developed in the 1950s, it was important in developing the theory of plate tectonics and in calibrating the geologic time scale.