However, paleontology as a whole encompasses all life, from bacteria to whales.
Paleontology does not usually deal with artifacts made by humans.
Paleontologists deal with two types of dating, absolute and relative.
Absolute dating, which estimates the age of a rock or fossil in years, is most usually done by measuring the amounts of a radioactive isotope and its decay product; since isotope decay rates are known to be constant, the age can be calculated from the relative amounts of parent isotope to daughter product.
Relative dating has been practiced for nearly 200 years, arising from the observation that different layers of sedimentary rock contain different fossils, and that this sequence can be recognized in other rocks at other localities, even those far away.
This allows fossil-bearing rocks to be dated relatively; on the basis of its fossils a rock might be placed in, say, the Ordovician Period, which followed the Cambrian Period and was followed by the Silurian Period.
This technique does not depend on knowing the actual numerical ages of the rocks.
Not all fossils are equally useful for relative dating, or correlation; some are rare, restricted to small geographic areas or to particular environments, difficult to recognize, or have such long ranges as to make precise correlation impossible.
There are a number of techniques and fields that deal with reconstructing the past, but paleontology provides hard data on past events.
Paleontology can potentially provide much data on the evolutionary relationships of organisms, which in turn gives a deeper understanding of biodiversity.
Although most of the fossils that paleontologists study are several thousands to several billions of years old, there is no absolute minimum age for a biological structure to be a fossil.