Geologists study the order that rocks and fossils appear and disappear, this study is called biostratigraphy.For example, if you find a ammonite and it was found near a Triassic rock then you know that the ammonite is 200 million years old.
However, you cannot determine the age of a fossil if the rocks nearby haven’t been previously dated.
This is where index fossils are used, they are known fossils that are used to date a specific time in earths history, the most useful index fossils must be recognisable, abundant, have a wide geography distribution and also only be around for a fairly short period of time.
To evaluate the exact age, both the chemical and physical properties of the object are looked keenly.
The main techniques used in absolute dating are carbon dating, annual cycle method, trapped electron method, and the atomic clocks.
Relative Dating and Absolute Dating are two types of such techniques which are under practice to determine the age of the fossils, objects or civilizations.
The relative dating is the technique in the Geology through which the age is determined with relation to the other objects.
Each isotope decays at a constant rate that is unique to that substance meaning that using the proportion of parent and daughter isotopes, you can calculate when the rock was formed.
Radiocarbon dating measures isotopes in organic material using the decay of carbon-14 to nitrogen-14.
This evaluation of the rocks and fossils in relative dating is known as the biostratigraphy.