What Is Absolute Dating Of Fossils

Absolute dating is an important scientific tool for examining fossils.

Dinosaurs, ancient creatures of the sea and early plant life have left behind a legacy of fossilized remains, clues to the nature of life on prehistoric Earth. Scientists have a variety of modern methods at their disposal for analyzing and understanding fossils and absolute dating is an important one. This process contributes to a better understanding of fossils and prehistoric life.


Before absolute dating of fossils became an option, scientists used another form of placing fossilized remains of life in history–relative dating. Unlike absolute dating, relative dating involved using the estimated geological age of the rock encasing a fossil and then comparing it to other rock specimens to determine the fossil’s “relative” age. Absolute dating originated in the 1920s after the discovery of radioactive isotopes–key tools in the process of absolute dating, states paleontologist Michael Benton, Ph.D., at ActionBioscience.org.


Also called radiometric dating, absolute dating uses the natural phenomenon of radioactive decay to determine the exact date of a fossil. According to the University of Alabama, six radioactive isotopes are useful for dating fossils: carbon 14, potassium 40, rubidium 87, thorium 232 and uranium 235 and 238. Each of these isotopes has a radioactive half-life, or a predictable amount of time during which radioactive particles are halved.


Absolute dating is done by chemists who measure the amount of radioactivity in a “parent element” in relation to its “daughter element” from the rock in which the fossil is found, giving a far more precise age for the fossil than relative dating. A parent isotope is a radioactive element such as uranium 235, and a daughter isotope is one that has gone through the process of radioactive decay and undergone a change in the periodic table’s atomic number–for instance, uranium 235 decays to the stable element lead.

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The most precise isotope used in absolute dating is Carbon 14, says ActionBioscience.org. Carbon 14 has a half-life of 5,730 years, though, and can only be used to measure the ages of fossils 70,000 years old or younger. For older fossils, scientists measure isotopes with much longer half-lives, such as uranium and potassium and compare them with their daughter isotopes.


Absolute dating is extremely precise compared with relative dating and invaluable for paleontologists in determining the nature of prehistoric life on Earth. Fossils are integral tools in providing scientists with records of major geological events such as massive earthquakes, as well as sudden mass extinctions, says ActionBioscience.org. Understanding the Earth’s past helps us to understand geological and biological changes that happen today.