Geologists often need to know the age of material that they find.
They use absolute dating methods, sometimes called numerical dating, to give rocks an actual date, or date range, in number of years.
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For example, the decay of potassium-40 to argon-40 is used to date rocks older than 20,000 years, and the decay of uranium-238 to lead-206 is used for rocks older than 1 million years.
Radiocarbon dating measures radioactive isotopes in once-living organic material instead of rock, using the decay of carbon-14 to nitrogen-14.
When ‘parent’ uranium-238 decays, for example, it produces subatomic particles, energy and ‘daughter’ lead-206.
Another example is luminescence dating, which measures the energy from radioactive decay that is trapped inside nearby crystals.But really, how do scientists figure out how old their dinosaur bones are?And, what about other findings like fossil fish, plants and insects?These rates of decay are known, so if you can measure the proportion of parent and daughter isotopes in rocks now, you can calculate when the rocks were formed.Because of their unique decay rates, different elements are used for dating different age ranges.Others measure the subatomic particles that are emitted as an isotope decays.Some measure the decay of isotopes more indirectly.This is different to relative dating, which only puts geological events in time Most absolute dates for rocks are obtained with radiometric methods.These use radioactive minerals in rocks as geological clocks.All radiometric dating methods measure isotopes in some way.Most directly measure the amount of isotopes in rocks, using a mass spectrometer.