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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.
Chronometric dating, also known as chronometry or absolute dating, is any archaeological dating method that gives a result in calendar years before the present time.
Archaeologists and scientists use absolute dating methods on samples ranging from prehistoric fossils to artifacts from relatively recent history.
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.
Each isotope is identified with what is called a ‘mass number’.Chronometric or calendar dating is a better choice.Using these methods, the scientist determines a date range for when an event took place rather than where it fits in the overall record. The techniques scientist need for absolute dating did not become available until the later half of the 20th century.Sedimentary rock is made of particles derived from other rocks, so measuring isotopes would date the original rock material, not the sediments they have ended up in.However, there are radiometric dating methods that can be used on sedimentary rock, including luminescence dating.