Scientists date igneous rock using elements that are slow to decay, such as uranium and potassium. By dating these surrounding layers, they can figure out the youngest and oldest that the fossil might be; this is known as bracketing the age of the sedimentary layer in which the fossils occur.

What is the most common way to date a rock?

Most absolute dates for rocks are obtained with radiometric methods. These use radioactive minerals in rocks as geological clocks. The atoms of some chemical elements have different forms, called isotopes. These break down over time in a process scientists call radioactive decay.

How is dating of rocks done?

To establish the age of a rock or a fossil, researchers use some type of clock to determine the date it was formed. Geologists commonly use radiometric dating methods, based on the natural radioactive decay of certain elements such as potassium and carbon, as reliable clocks to date ancient events.