Absolute and relative dating of rock
There are two main methods determining a fossils age, relative dating and absolute dating.
Relative dating is used to determine a fossils approximate age by comparing it to similar rocks and fossils of known ages.
On the other hand, the half-life of the isotope potassium 40 as it decays to argon is 1.26 billion years.
So carbon 14 is used to date materials that aren’t that old geologically, say in the tens of thousands of years, while potassium-argon dating can be used to determine the ages of much older materials, in the millions and billions year range.
Relative age dating also means paying attention to crosscutting relationships.
Geologists draw on it and other basic principles ( to determine the relative ages of rocks or features such as faults.Pretty obvious that the dike came after the rocks it cuts through, right?With absolute age dating, you get a real age in actual years.For example, which is older, the bricks in a building or the building itself?Are there repairs or cracks in the sidewalk that came after the sidewalk was built?
In a way this field, called geochronology, is some of the purest detective work earth scientists do.