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Stone age site gets pushed back in time.

Stone Age site gets pushed back in time

More than 20 years ago, the potassium argon technique for calculating the age of ancient rocks revealed that early hominid sites at Olduvai Gorge in East Africa dated to 1.8 million years ago, a much older estimate than had generally been recognized. The same method, which depends on the decay of potassium's naturally radioactive isotope to the nonradioactive gas argon, now has significantly pushed back the age of another East African site containing remains of later homind activity during the Stone Age.

Artifact-bearing layers of volcanic ash at the Olorgesailie river basin in Kenya were formerly estimated to be about 500,000 years old, but now are more accurately dated at 700,000 to 900,000 years old, report Bethany A. Bye of the University of Utah in Salt Lake City and her colleagues in the Sept. 17 NATURE.

Large numbers of stone hand-axes have been uncovered at Olorgesailie (SN: 4/25/87, p.264), which is considered a key site of the Stone Age Acheulean culture. The almond-shaped axes are the primary Acheulean remains. The Acheulean era ranged from about 1.4 million to 150,000 years ago, but within that expanse there are few well-dated points at which cultural change can be examined.

In addition to revising the age of artifact-rich portions of the Olorgesailie site, Bye and her co-workers found that lower layers of volcanic ash differ chemically from overlying layers that contain the abundant Acheulean remains. They suggest that the lower and upper layers were created by separate volcanic eruptions.

According to J.A.J. Gowlett of the University of Liverpool, England, writing in the same NATURE, the aging of Olorgesailie leaves researchers wondering whether they can confidently place any African hominid sites in the period between 700,000 and 300,000 years ago.
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Title Annotation:at Olduvai Gorge in Kenya
Author:Bower, B.
Publication:Science News
Date:Sep 26, 1987
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