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How does potassium-argon dating help date early human remains in East Africa?

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Archaeology Archaeologists mapping their finds at Pachacamac, Peru, an Indigenous town occupied from approximately 200 bce to 1532 ce, when it was sacked by conquistadors under the command of Francisco Pizarro.

Potassium-argon dating is a vital absolute dating technique used to determine the age of early human remains in East Africa by analyzing volcanic materials found in the same geological strata as the fossils.1

Because East Africa’s Eastern Rift Valley has experienced significant geologic and volcanic activity, layers of volcanic ash have periodically covered the landscape. These ash deposits contain minerals that trap radioactive potassium-40. Over time, this isotope decays into argon-40 at a known, constant rate. By measuring the ratio of these isotopes within the volcanic rock, scientists can calculate the time elapsed since the ash layer was deposited.2345

Archaeologists use this method to date the specific volcanic strata above and below hominin remains, effectively "bracketing" the fossils within a precise chronological window. This technique has been instrumental in establishing that early human ancestors and their artifacts in East Africa date back at least 2,000,000 years.21