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Why are South African Australopithecus fossils difficult to date precisely?
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Australopithecus
Artist's rendering of Australopithecus afarensis, which lived from 3.8 to 2.9 million years ago.
South African Australopithecus fossils are difficult to date precisely because the volcanic sediments required for argon radiometric dating—a technique commonly used to provide accurate ages for fossils in eastern Africa—are absent in South Africa.1
Because these radiometric methods cannot be applied directly to the South African cave deposits, researchers must instead approximate the age of the fossils using stratigraphy. This process involves correlating the fossil-bearing layers with other sites by identifying time-diagnostic animal species found within the same deposits.1