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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.
Because of the fairly fast decay rate of carbon-14, it can only be used on material up to about 60,000 years old.
Geologists use radiocarbon to date such materials as wood and pollen trapped in sediment, which indicates the date of the sediment itself.
When ‘parent’ uranium-238 decays, for example, it produces subatomic particles, energy and ‘daughter’ lead-206.
Some measure the decay of isotopes more indirectly.The atoms of some chemical elements have different forms, called isotopes.These break down over time in a process scientists call radioactive decay.This law was independently discovered by William Smith (1769-1839), a British engineer, while working on excavations for canals in England (Winchester, 2002 p.131) and by Georges Cuvier (1769-1832), a French anatomist, and Alexandre Brongniart (1770-1847), a French naturalist and geologist, during their work on the deposits of the Paris Basin.