Numerical age dating methods
For example, based on the primate fossil record, scientists know that living primates evolved from fossil primates and that this evolutionary history took tens of millions of years.
By comparing fossils of different primate species, scientists can examine how features changed and how primates evolved through time.
Layers of rock are deposited horizontally at the bottom of a lake (principle of original horizontality).
Younger layers are deposited on top of older layers (principle of superposition).
There are three general approaches that allow scientists to date geological materials and answer the question: "How old is this fossil?The layers of rock at the base of the canyon were deposited first, and are thus older than the layers of rock exposed at the top (principle of superposition).In the Grand Canyon, the layers of strata are nearly horizontal.The age of the fossil must be determined so it can be compared to other fossil species from the same time period.
Understanding the ages of related fossil species helps scientists piece together the evolutionary history of a group of organisms.
Most sediment is either laid down horizontally in bodies of water like the oceans, or on land on the margins of streams and rivers.