Absolute and Relative Dating Methods

Absolute vs. Relative Dating

Absolute dating methods allow a researcher to determine the age of a sample in years whereas relative dating methods only allow scientists to determine that a given sample is older or younger than a reference sample. For example, using an absolute dating method, like radiometric dating described below, you could determine that a tooth from the La Brea Tar Pits is 11,050 years old. A relative dating method, like comparing fossil sequences in sedimentary rocks from around the world, will only able to conclude that a sample is older than a particular layer of rock or another sample.

Radiometric Dating:

Naturally occurring isotopes such as radioactive carbon (¹⁴C) make possible the dating of many rocks and fossils. The ratio of the radioactive isotope ¹⁴C to the stable ¹²C, for instance, is relatively constant in the carbon dioxide of the atmosphere, but once a plant has captured a CO² molecule and built it into a product like sucrose or cellulose, the decay of ¹⁴C atoms to ¹²C causes a ratio of ¹⁴C to ¹²C to decline steadily with time. The older the sample, the lower the amount of ¹⁴C and the higher the amount of ¹²C. Hence, the ¹⁴C:¹²C ratio in a sample provides a moderately accurate measure of age.

Supplementary Link:

• Relative dating

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