Anthropologists say the discovery of stone tools found in north-west Kenya dating back 3.3 million years challenges the mainstream story of mankind.
They are 700,000 years older than any other such stone tools ever found.
"The tools we have unearthed are the very first fossil traces of techniques bequeathed by our hominin ancestors 3.3 million years ago," said French researcher Sonia Harmand of New York's Stony Brook University.
"Our discovery also refutes the long-standing theory that Homo habilis was the first maker of tools."
Tool-making, like fire-making and farming, is considered a key moment in the ascent of humans.
The theory is that tools emerged to help hominins — the term for modern and extinct species of humans — butcher animals, unlocking protein that in turn helped the evolution of bigger brains.
But crafting a tool, by hitting a stone with another stone, requires conceptual and motor skills.
Until now, these were thought to be beyond the ape-like hominins who lived before habilis, whose "handy man" name comes from his apparent dexterity.
Habilis, bigger-brained than previous hominins and an ancestor of Homo sapiens, lived between roughly 2.8 million and 1.5 million years ago. The earliest tools in the Habilis era date from around 2.6 million years ago.
The tool discovery was made in the Nachukui Formation, a remote site in scrublands west of Lake Turkana that has yielded a series of remarkable finds since the mid-1980s.
It came through a stroke of luck, when Ms Harmand and her colleague Jason Lewis went on a scouting trip one morning in July 2011 and got lost.
Seeking their way back, they climbed a hill to get a better view and got a strange feeling "that something was special about this particular place".
With the help of a local tribesman, they explored craggy outcrops which yielded the first of these ancient treasures.
The haul, described in the journal Nature, comprises 149 artefacts, from stone cores and flakes to rocks used for hammering.
The stones were found just above a layer of volcanic ash dated through argon isotopes to about 3.3 million years ago.
This estimate was confirmed by measuring telltale shifts in Earth's magnetic fields in iron-bearing minerals in sediment where the tools were found.