Fossils are primarily used in relative dating rather than absolute dating. Relative dating helps to determine the order of events and ages of rock layers (strata) by examining their position and the type of fossils they contain, but it does not provide an exact age in years.
Absolute dating, on the other hand, involves techniques that provide a numerical age or range in years for rocks and fossils. This typically includes methods like radiometric dating, where the decay of radioactive isotopes in minerals is measured (e.g., carbon dating for organic materials or uranium-lead dating for older rocks).
However, fossils can play an indirect role in absolute dating. The presence of certain fossils, known as index fossils, can help geologists correlate rock layers across different regions. When these index fossils are found in rock layers that have been dated using absolute dating methods, they can provide context and help assign ages to other rock layers based on their fossil content.
In summary, while fossils themselves do not provide absolute ages, they can be valuable in conjunction with absolute dating techniques to understand the timing of geological events and the age of rock formations.