So in order to date most older fossils, scientists look for layers of igneous rock or volcanic ash above and below the fossil.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.

radiometric dating science definition-45

Radiometric dating science definition video

Geologists use radiometric dating to estimate how long ago rocks formed, and to infer the ages of fossils contained within those rocks. The universe is full of naturally occurring radioactive elements.

Radioactive atoms are inherently unstable; over time, radioactive “parent atoms” decay into stable “daughter atoms.” When molten rock cools, forming what are called igneous rocks, radioactive atoms are trapped inside. By measuring the quantity of unstable atoms left in a rock and comparing it to the quantity of stable daughter atoms in the rock, scientists can estimate the amount of time that has passed since that rock formed.

Bracketing the fossils Fossils are generally found in sedimentary rock—not igneous rock.

Sedimentary rocks can be dated using radioactive carbon, but because carbon decays relatively quickly, this only works for rocks younger than about 50 thousand years.

Radiometric dating methods are used to establish the geological time scale.

All ordinary matter is made up of combinations of chemical elements, each with its own atomic number, indicating the number of protons in the atomic nucleus.

Elements exist in different isotopes, with each isotope of an element differing in the number of neutrons in the nucleus.

The method compares the amount of a naturally occurring radioactive isotope and its decay products, in samples. It is the main way to learn the age of rocks and other geological features, including the age of the Earth itself.

It may be used to date a wide range of natural and man-made materials.