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. Potassium-argon dating, method of determining the time of origin of rocks by measuring the ratio of radioactive argon to radioactive potassium in the rock. Potassium-Argon dating has the advantage that the argon is an inert gas that does found inside a rock is very likely the result of radioactive decay of potassium. . in the fossil record, much effort was devoted to dating it with potassium-argon.
So they're all going to have a certain amount of potassium in it. And so for every one of these argon's you know that there must have been 10 original potassium's.
Dating Fossils – How Are Fossils Dated?