Dating rocks using radioactive decay Nakedchatrandom
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Segment from A Science Odyssey: "Origins."Geologists have calculated the age of Earth at 4.6 billion years.
But for humans whose life span rarely reaches more than 100 years, how can we be so sure of that ancient date? Even the Greeks and Romans realized that layers of sediment in rock signified old age.
The results showed that Ötzi died over 5000 years ago, sometime between 33 BC. Uranium has a very long half-life and so by measuring how much uranium is left in a rock its approximate age can be worked out.
Geologist Ralph Harvey and historian Mott Greene explain the principles of radiometric dating and its application in determining the age of Earth.
For example, in 1991, two hikers discovered a mummified man, preserved for centuries in the ice on an alpine mountain.