Radiometric dating. Geologists use radiometric dating to estimate how long ago rocks formed, and to infer the ages of fossils contained within those rocks. When molten rock cools, forming what are called igneous rocks, radioactive atoms are trapped inside. Afterwards, they decay at a predictable rate.

Can igneous rocks be numerically dated?

Of the three basic rock types, igneous rocks are most suited for radiometric dating. Metamorphic rocks may also be radiometrically dated. However, radiometric dating generally yields the age of metamorphism, not the age of the original rock.

Why are igneous rocks best for radiometric dating?

Igneous rocks are the best types of rock samples to use for radiometric dating. When igneous rock forms, elements are separated into different minerals in the rock. Thus, when they form, minerals in igneous rocks often contain only a parent isotope and none of the daughter isotope.

What is the oldest layer of rock?

bottom layer As you read earlier, sedimentary rocks form from the sediments that fall to the bottom of lakes, rivers, and seas. Over time, the sediments pile up to form horizontal layers of sedimentary rocks. The bottom layer of rock forms first, which means it is oldest.

What is the oldest sedimentary rock layer?

Over time, the sediments pile up to form horizontal layers of sedimentary rocks. The bottom layer of rock forms first, which means it is oldest. Each layer above that is younger, and the top layer is youngest of all.