Biostratigraphy: One of the first and most basic scientific dating methods is also one of the easiest to understand.
Layers of rock build one atop another — find a fossil or artifact in one layer, and you can reasonably assume it’s older than anything above it.
Both plants and animals exchange carbon with their environment until they die.
Afterward, the amount of the radioactive isotope carbon-14 in their remains decreases.
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.