Researchers can measure the amount of these trapped electrons to establish an age.
But to use any trapped charge method, experts first need to calculate the rate at which the electrons were trapped.
The uranium-thorium method is often helpful for dating finds in the 40,000- to 500,000-year-old range, too old for radiocarbon but too young for K-Ar or Ar-Ar.
Over time, certain kinds of rocks and organic material, such as coral and teeth, are very good at trapping electrons from sunlight and cosmic rays pummeling Earth.
Both plants and animals exchange carbon with their environment until they die.
The polarity is recorded by the orientation of magnetic crystals in specific kinds of rock, and researchers have established a timeline of normal and reversed periods of polarity.
While K-Ar dating requires destroying large samples to measure potassium and argon levels separately, Ar-Ar dating can analyze both at once with a single, smaller sample.
Uranium series dating: U-series dating includes a number of methods, each based on different uranium isotopes’ decay rates.
Unlike observation-based relative dating, most absolute methods require some of the find to be destroyed by heat or other means.
This family of dating methods, some more than a century old, takes advantage of the environment’s natural radioactivity.