Is thermoluminescence dating
Tephrochronology: Within hours or days of a volcanic eruption, tephra — fragments of rock and other material hurled into the atmosphere by the event — is deposited in a single layer with a unique geochemical fingerprint.
Researchers can first apply an absolute dating method to the layer.
Whenever possible, researchers use one or more absolute dating methods, which provide an age for the actual fossil or artifact.
Unlike observation-based relative dating, most absolute methods require some of the find to be destroyed by heat or other means.
Generally speaking, the more complex a poem or piece of pottery is, the more advanced it is and the later it falls in the chronology.
Before more precise absolute dating tools were possible, researchers used a variety of comparative approaches called relative dating.
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.
Paleomagnetism: Earth’s magnetic polarity flip-flops about every 100,000 to 600,000 years.
Cases like this in China, Russia and even New Zealand with other geological eras has slowed down the uniform organization of the stratigraphic record.
When it comes to determining the age of stuff scientists dig out of the ground, whether fossil or artifact, “there are good dates and bad dates and ugly dates,” says paleoanthropologist John Shea of Stony Brook University.
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.