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.
Sometimes only one method is possible, reducing the confidence researchers have in the results. “They’re based on ‘it’s that old because I say so,’ a popular approach by some of my older colleagues,” says Shea, laughing, “though I find I like it myself as I get more gray hair.” Kidding aside, dating a find is crucial for understanding its significance and relation to other fossils or artifacts.
Afterward, the amount of the radioactive isotope carbon-14 in their remains decreases.
Paleontologists still commonly use biostratigraphy to date fossils, often in combination with paleomagnetism and tephrochronology.
A submethod within biostratigraphy is faunal association: Sometimes researchers can determine a rough age for a fossil based on established ages of other fauna from the same layer — especially microfauna, which evolve faster, creating shorter spans in the fossil record for each species.
This includes factoring in many variables, such as the amount of radiation the object was exposed to each year.
These techniques are accurate only for material ranging from a few thousand to 500,000 years old — some researchers argue the accuracy diminishes significantly after 100,000 years.
Measuring carbon-14 in bones or a piece of wood provides an accurate date, but only within a limited range.