Carbon relative and radioactive dating
While people are most familiar with carbon dating, carbon dating is rarely applicable to fossils.Carbon-14, the radioactive isotope of carbon used in carbon dating has a half-life of 5730 years, so it decays too fast.It can only be used to date fossils younger than about 75,000 years.
Typically commonly occurring fossils that had a widespread geographic distribution such as brachiopods, trilobites, and ammonites work best as index fossils.
It’s often much easier to date volcanic rocks than the fossils themselves or the sedimentary rocks they are found in.
So, often layers of volcanic rocks above and below the layers containing fossils can be dated to provide a date range for the fossil containing rocks.
Absolute dating is used to determine a precise age of a rock or fossil through radiometric dating methods.
This uses radioactive minerals that occur in rocks and fossils almost like a geological clock.