The age of which index fossil could be determined by using carbon - 14?

The age which index fossils can determine by use of carbon-14 is referred to as radiocarbon dating which uses carbon 14 isotopes.

Carbon-14 dating is referred to as a method which determines the age of an object which contains organic material by use of properties of the radioactive isotope of carbon.

Radiocarbon-14 is constantly being created in the atmosphere which interacts with cosmic rays, which has atmospheric nitrogen. When an animal dies, it stops exchanging carbon with its environment, where the amount of carbon-14 which it had begins to decrease and then it undergoes radioactive decay.