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How were Homo habilis fossils at Olduvai Gorge dated?

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An illustration of Homo habilis, an early human ancestor, shown walking upright with a hairy body and ape-like features. A scale beside the figure indicates height in inches and centimeters. — Homo habilis Artist's rendering of *Homo habilis*, which lived from 2 to 1.5 million years ago.

Several approaches have been used to establish a timescale for Homo habilis fossils at Olduvai Gorge, where the fossil beds accumulated in a lake basin characterized by volcanic activity.12

Because the site contains layers of volcanic ash and lava flows, researchers have utilized potassium-argon dating to determine the age of the deposits. This method measures the ratio of radioactive potassium-40 to its decay product, argon-40, within volcanic minerals. By dating these volcanic strata, scientists can estimate the age of the fossils found within or between specific geological layers, such as Bed I and Bed II.2341

While radiometric dating provides a primary framework, other dating methods are employed when direct radiometric dates are unavailable for specific specimens. Through these combined techniques, researchers have determined that H. habilis remains at Olduvai generally date from approximately 1.5 to 1.9 million years ago.1