Dating rocks and fossils and geologic events

The universe is full of naturally occurring radioactive elements.Radioactive atoms are inherently unstable; over time, radioactive "parent atoms" decay into stable "daughter atoms." When molten rock cools, forming what are called igneous rocks, radioactive atoms are trapped inside. By measuring the quantity of unstable atoms left in a rock and comparing it to the quantity of stable daughter atoms in the rock, scientists can estimate the amount of time that has passed since that rock formed.

Relative dating is used to determine a fossils approximate age by comparing it to similar rocks and fossils of known ages.

Absolute dating is used to determine a precise age of a fossil by using radiometric dating to measure the decay of isotopes, either within the fossil or more often the rocks associated with it.

While people are most familiar with carbon dating, carbon dating is rarely applicable to fossils.

Carbon-14, the radioactive isotope of carbon used in carbon dating has a half-life of 5730 years, so it decays too fast.

The majority of the time fossils are dated using relative dating techniques.

Using relative dating the fossil is compared to something for which an age is already known.Index fossils are fossils that are known to only occur within a very specific age range.Typically commonly occurring fossils that had a widespread geographic distribution such as brachiopods, trilobites, and ammonites work best as index fossils.The atoms in some chemical elements have different forms, called isotopes.These isotopes break down at a constant rate over time through radioactive decay.So in order to date most older fossils, scientists look for layers of igneous rock or volcanic ash above and below the fossil.

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