Geologists use radiometric dating to estimate how long ago rocks formed, and to infer the ages of fossils contained within those rocks. Radioactive elements decay The universe is full of naturally occurring radioactive elements. Radioactive atoms radiometric dating metamorphic rocks inherently unstable; over time, radioactive "parent atoms" decay radiometric dating metamorphic rocks stable "daughter atoms.
When molten rock cools, forming what are called igneous rocks, radioactive atoms are trapped inside. Afterwards, they decay at a predictable rate. 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. 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.
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 radiometric dating metamorphic rocks youngest and oldest that the fossil might be; this is known as "bracketing" the age of the sedimentary layer in which the fossils occur.
Read more about how radiometric dating factored into the history of evolutionary thought. Teach your students about absolute dating: Determining age of rocks and fossilsa classroom activity for grades Find datijg lessons, activities, videos, and articles that focus on radikmetric and absolute dating. Home About Copyright Credits Contact Metmorphic Translations Read how others have recognized the Understanding Evolution website.