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.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.
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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.
Paleontologists still commonly use biostratigraphy to date fossils, often in combination with paleomagnetism and tephrochronology.
They then use that absolute date to establish a relative age for fossils and artifacts in relation to that layer. Anything below the Taupo tephra is earlier than 232; anything above it is later.
For example, New Zealand’s massive Taupo volcano erupted in A. Relative chronology: Researchers have often constructed timelines of a culture or civilization based on the stylistic evolution of its decorative or dramatic arts — that’s why the method is also sometimes called stylistic seriation.