“Peking Man” Older Than First Thought

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March 12, 2009

A new dating method indicates the stone tools found at Zhoukoudian in China are considerably older than first believed, according to a paper published in the journal Nature this week.  Zhoukoudian, not far from Beijing, then called Peking in the West, is the site of a cave first excavated by Franz Weidenreich starting in the late Twenties and during the decade of the Thirties.  Fossilized remains of a hominin later attributed to Homo erectus and stone tools were found and said to be between 230,000 and half a million years old in accordance with the dating methods then in use.  The new method, called aluminum-26/beryllium-10, established dates of between 680 and 780 thousand years ago.
The further significance of this is redating is that the older dates correspond with a cooler period in Earth’s geologic history and indicate Homo erectus, having migrated out of Africa a million years before, was adapting to a far colder climate. 
The aluminum-26/beryllium-10 radiometric method is described by Purdue University Prof. Darryl Granger, lead author of the Nature paper, as measuring the radioactive decay of isotopes of the two metals in the mineral quartz. As cosmic rays penetrate into rocks at the Earth's surface, chemical reactions produce these isotopes of aluminum and beryllium. If the rocks are then buried, the isotopes are no longer produced and those existing begin to decay. The rate of decay can tell researchers when the rocks were deposited in a site, he said. [Quoted in AScribe, the public interest newsletter. ]
Many of the fossils found by Weidenreich disappeared as he sought to get them to safety in the face of the onrushing Japanese invasion of Northern China in the late Thirties.   He gave them to a U.S. Marine in a Chinese port city, to be placed aboard a ship bound for San Francisco; they were never seen again.

Here is the cave at Zhoukoudian:

Cabe at Zhoukoudian

By permission, Nature Publishing Group

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