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How we know what happened when
Life began 3.8 billion years ago, and insects diversified 290 million years ago, but the human
and chimpanzee lineages diverged only five million years ago. How have scientists figured out the
dates of long past evolutionary events? Here are some of the methods and evidence that scientists
use to put dates on events:
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1. Radiometric dating relies on half-life decay of radioactive elements
to allow scientists to date rocks and materials directly. |
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2. Stratigraphy provides a sequence of events from which relative dates can
be extrapolated. |
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3. Molecular clocks allow scientists to use the amount of genetic divergence
between organisms to extrapolate backwards to estimate dates. |
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