Archaeologists say stone tools recently unearthed in Kenya are the oldest ever found, at least 700,000 years older than any discovered before.

The stone flake tools found along the shores of the African country's Lake Turkana have been dated to 3.3 million years ago, they report, strong evidence that our earliest ancestors were making and using tools hundreds of thousands of years before the modern Homo lineage arose around 2.8 million years ago.

The area around Lake Turkana has yielded many fossils of early humans and their tools; a team headed by Sonia Harmand of Stony Brook University in New York made the latest discovery.

Previously, the oldest stone tools known had been 2.6-milion-year-old items found in Ethiopia.

Then, in 2010, researchers also working in Ethiopia announced the discovery of animal bones from 3.4 million years ago bearing cut marks, suggesting humans made the cuts using stone tools.

There was considerable controversy and debate over that claim, but the newly discovered Kenyan tools — and their 3.3-million-year age — strongly supports the possibility of tool use earlier than had been suspected before, researchers say.

"The artifacts were clearly knapped and not the result of accidental fracture of rocks," Harmand told the annual meeting of the Paleoanthropology Society being held this week in San Francisco.

Knapping is the process of chipping flakes off a larger stone, flakes that possess sharp edges that can be used to cut plants, nuts or meat.

The discovery of the tools was an accident, Harmand says; her team had been looking for remains of an ancient human relative, Kenyanthripos platyops, when they took a wrong turn and ended up at a different site known as Lomekwi 3, just to the west of Lake Turkana.

After finding some tools on the surface, they dug deeper and eventually recovered almost 20 preserved flakes, source stones and anvils used as bases on which to knapp stones.

Experts who've examined the tools say some are very crudely made while others are a bit more sophisticated.

While not as advanced as most early human-created tools found previously, "there's no doubt it's purposeful" tool-making, says Richard Potts, who heads the Human Origins Program at the Smithsonian Institution.

The 700,000-year gap between the Kenyan tools and the previously oldest known examples suggests the knowledge of how to make them could have died out with those early human ancestors and then been "reinvented" several millennia later, scientists say.

Still, the new discovery identifies an earlier starting point in our attempts to track human evolution, Harmand suggests.

"The Lomekwi 3 tools mark a new beginning to the known archaeological record," she says.

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