The combination of absolute and relative dating allows scientists to determine the ages of rocks and fossils. Absolute dating provides evidence that helps us estimate the ages of Earth. How can scientists find the absolute age of igneous rocks?

By radiometric dating

Explanation:

The relative age of a rock sample is determined by comparing a  (or the fossils it contains) to other layers. Relative age of a rock sample can be determined by looking at the position of various rock layers.

Absolute age of a rock sample is the numerical.  Absolute age can be determined by using radiometric dating.

According to Oxford dictionary, radiometric dating is "a method of dating geological specimens by determining the relative proportions of particular radioactive isotopes present in a sample."