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.

How do radiometric dating help in understanding the Earth?

Radiometric dating, which relies on the predictable decay of radioactive isotopes of carbon, uranium, potassium, and other elements, provides accurate age estimates for events back to the formation of Earth more than 4.5 billion years ago.

What is the importance of geologic time?

The geologic time scale is an important tool used to portray the history of the Earth—a standard timeline used to describe the age of rocks and fossils, and the events that formed them.