The atoms of some chemical elements have different forms, called isotopes.These break down over time in a process scientists call radioactive decay.Dating techniques are procedures used by scientists to determine the age of an object or a series of events.The two main types of dating methods are relative and absolute.If you're seeing this message, it means we're having trouble loading external resources on our website.If you're behind a web filter, please make sure that the domains *.and *.are unblocked.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.
Another example is luminescence dating, which measures the energy from radioactive decay that is trapped inside nearby crystals.
Each original isotope, called the parent, gradually decays to form a new isotope, called the daughter.
Each isotope is identified with what is called a ‘mass number’.
Since certain species of animals existed on Earth at specific times in history, the fossils or remains of such animals embedded within those successive layers of rock also help scientists determine the age of the layers.
Similarly, pollen grains released by seed-bearing plants became fossilized in rock layers.