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Here of some of the well-tested methods of dating used in the study of early humans:
- 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.
- Thermo-luminescence, Optically stimulated luminescence, and Electron spin resonance. All of these methods measure the amount of electrons that get absorbed and trapped inside a rock or tooth over 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.
- Biochronology. Since animal species change over time, the fauna can be arranged from younger to older. At some sites, animal fossils can be dated precisely by one of these other methods. For sites that cannot be readily dated, the animal species found there can be compared to well-dated species from other sites. In this way, sites that do not have radioactive or other materials for dating can be given a reliable age estimate.
- 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.
If you would like to learn more, we recommend visiting the 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.