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  • Potassium-argon dating, Argon-argon dating, Carbon-14 (or Radiocarbon), and Uranium series. All of these methods measure the amount of radioactive decay of chemical elements; the decay occurs in a consistent manner, like a clock, over long periods of time.
  • Paleomagnetism. This method compares the direction of the magnetic particles in layers of sediment to the known worldwide shifts in Earth’s magnetic field, which have well-established dates using other dating methods.
  • Molecular clock. This method compares the amount of genetic difference between living organisms and computes an age based on well-tested rates of genetic mutation over time.  Since genetic material (like DNA) decays rapidly, the molecular clock method can’t date very old fossils. It’s mainly useful for figuring out how long ago living species or populations shared a common ancestor, based on their DNA.

Chart of human evolution milestones and dating methods.

If you would like to learn more, we recommend visiting these two websites:

1. The Dating Rocks and Fossils Using Geological Methods article in Nature's excellent Scitable series of online articles in the Nature Education Knowledge Project.

2. University of California, Berkeley Museum of Paleontology's Understanding Deep Time online resource. This is an informational tour in which students gain a basic understanding of geologic time, the evidence for events in Earth’s history, relative and absolute dating techniques, and the significance of the Geologic Time Scale.

Page last updated: September 14, 2018