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The Associated Press
In this undated photo made available in May 2015 by the Mission Prehistorique au Kenya - West Turkana Archaeological Project, Sonia Harmand and Jason Lewis hold stone tools found in the West Turkana area of Kenya. The artifacts, dated at 3.3 million years old, are much older than the earliest known trace of our own branch of the evolutionary family tree. So it’s a new challenge to the traditional idea that only members of our branch made stone tools. The discovery was reported in the journal Nature on Wednesday, May 20, 2015.

NEW YORK — Scientists say they've found the oldest stone tools ever discovered, pushing back the history of tool-making by about 700,000 years.

The artifacts, found in Kenya, are 3.3 million years old. They are much older than the earliest known trace of our own branch of the evolutionary family tree. So it's a new challenge to the traditional idea that only members of our branch made stone tools.

Such tools were made by striking stones to knock off sharp-edged flakes, which could be used for cutting. But so far, nobody knows who made the Kenyan tools, or what they were used for.

The discovery was reported Wednesday in the journal Nature.

Online: http://www.nature.com/nature