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Radioactive dating techniques are based on

Researchers can first apply an absolute dating method to the layer.

Egyptologists, for example, created a relative chronology of pre-pharaonic Egypt based on increasing complexity in ceramics found at burial sites.

Whenever possible, researchers use one or more absolute dating methods, which provide an age for the actual fossil or artifact.

It would be like having a watch that told you day and night.” Single crystal fusion: Also called single crystal argon or argon-argon (Ar-Ar) dating, this method is a refinement of an older approach known as potassium-argon (K-Ar) dating, which is still sometimes used.

Both methods date rock instead of organic material. But unlike radiocarbon dating, the older the sample, the more accurate the dating — researchers typically use these methods on finds at least 500,000 years old.

Before more precise absolute dating tools were possible, researchers used a variety of comparative approaches called relative dating.

These methods — some of which are still used today — provide only an approximate spot within a previously established sequence: Think of it as ordering rather than dating.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.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.Paleomagnetism is often used as a rough check of results from another dating method.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.Paleomagnetism: Earth’s magnetic polarity flip-flops about every 100,000 to 600,000 years.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.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.The good dates are confirmed using at least two different methods, ideally involving multiple independent labs for each method to cross-check results.

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