New York: By taking a wrong turn in a dry riverbed in Kenya, scientists discovered a trove of stone tools far older than any ever found before.

Nobody knows who made them - or why.

Sonia Harmand and Jason Lewis with stone tools found in the West Turkana area of Kenya.

At 3.3 million years old, they push back the record of stone tools by about 700,000 years.

More significantly, they are half-a-million years older than any known trace of our own branch of the evolutionary tree.