There are two main methods determining a fossils age, relative dating and absolute dating.
Carbon dating has given archeologists a more accurate method by which they can determine the age of ancient artifacts.
Libby invented carbon dating for which he received the Nobel Prize in chemistry in 1960.
This uses radioactive minerals that occur in rocks and fossils almost like a geological clock.
It’s often much easier to date volcanic rocks than the fossils themselves or the sedimentary rocks they are found in.
Then after another 5,000 years half of the remaining parent isotope will have decayed.