Anthropology dating techniques
Absolute dating methods are methods that return a specific date, in years, for the formation of a fossil or sediment layer.
Often this date is given as a range of years, for example, 3.5 mya /- 35ky (that would be read as 3.5 million years ago, plus or minus 35 thousand years).
Anthropologists place the human individual, community, and population back into the environment and attempt to understand how humans interacted with that environment.
These date different materials and different types of events.
They also have different ranges over which they are effective (that is, they can't be used for materials that are older or younger than their effective range).
To greatly simplify, radiometric dates work by counting the number of atoms that have decayed from a radioactive to a more stable isotope and then figuring out how many half-lives have passed.
For example, 14C (carbon-14) has a half-life of 5,730 years.