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08-Apr-2019 20:07

This uses radioactive minerals that occur in rocks and fossils almost like a geological clock.

It’s often much easier to date volcanic rocks than the fossils themselves or the sedimentary rocks they are found in.

We define the rate of this radioactive decay in half-lives.

If a radioactive isotope is said to have a half-life of 5,000 years that means after 5,000 years exactly half of it will have decayed from the parent isotope into the daughter isotopes.

Studying the layers of rock or strata can also be useful. If a layer of rock containing the fossil is higher up in the sequence that another layer, you know that layer must be younger in age. This can often be complicated by the fact that geological forces can cause faulting and tilting of rocks.

Absolute dating is used to determine a precise age of a rock or fossil through radiometric dating methods.


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For example if you have a fossil trilobite and it was found in the Wheeler Formation.Carbon-14, the radioactive isotope of carbon used in carbon dating has a half-life of 5730 years, so it decays too fast.It can only be used to date fossils younger than about 75,000 years.Potassium-40 on the other hand has a half like of 1.25 billion years and is common in rocks and minerals.

This makes it ideal for dating much older rocks and fossils.

Subtract one from the other and I'll have a rough-cut figure for how many were made. PRII owners were kind enough to start sending their serial numbers in.

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