As these changes have occurred, organisms have evolved, and remnants of some have been preserved as fossils.A fossil can be studied to determine what kind of organism it represents, how the organism lived, and how it was preserved.By comparing fossils of different primate species, scientists can examine how features changed and how primates evolved through time.However, the age of each fossil primate needs to be determined so that fossils of the same age found in different parts of the world and fossils of different ages can be compared.However, by itself a fossil has little meaning unless it is placed within some context.
This method relies on the uptake of a naturally occurring radioactive isotope of carbon, carbon-14 by all living things.
A commonly used radiometric dating technique relies on the breakdown of potassium (Ar in an igneous rock can tell us the amount of time that has passed since the rock crystallized.
If an igneous or other rock is metamorphosed, its radiometric clock is reset, and potassium-argon measurements can be used to tell the number of years that has passed since metamorphism.
Since the 1950s, geologists have used radioactive elements as natural "clocks" for determining numerical ages of certain types of rocks. "Forms" means the moment an igneous rock solidifies from magma, a sedimentary rock layer is deposited, or a rock heated by metamorphism cools off.
It's this resetting process that gives us the ability to date rocks that formed at different times in earth history.