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Our ancestors started using fire at least a million years ago and cooking may have played a key role in our evolution.

But could early humans light fires, and if so how did they do it? In the case of the Neanderthals at least, we may finally have an answer.

Dozens of 50,000-year-old hand axes from around Europe have tiny scratches on their flat sides, Andrew Sorensen of Leiden University in the Netherlands and colleagues have shown. And the mostly likely explanation, they argue, is that the axes were used to strike sparks.

鈥淭he hand axe was like a Swiss Army knife for Neanderthals,鈥� says Sorensen. In addition to being used for cutting, he thinks the axe was held in one hand and a piece of iron pyrites struck against the flat side with the other hand to create sparks. The flat sides of a hand axe are rough and ideal for striking sparks.

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Sorensen can light a fire in as little as 10 seconds this way (see video, below). 鈥淚t鈥檚 quite an effective method,鈥� he says.

What鈥檚 more, it creates the same patterns of scratches as those seen on ancient axes. 鈥淭hese traces match what we are able to produce during fire-making experiments,鈥� Sorensen says. 鈥淎nd using the flat side, as I鈥檓 sure the Neanderthals knew, helps to keep the edges of the tool sharp for other tasks.鈥�

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Iron pyrites corrodes once exposed to air, so the small pieces used to strike sparks would be preserved only in exceptional circumstances 鈥� and none has yet been found. So the evidence is not completely conclusive, Sorensen says, but it is 鈥減retty solid鈥�.

鈥淚 believe this is the first evidence that Neanderthals could make fire,鈥� says Richard Wrangham of Harvard University, who thinks fire shaped human evolution. 鈥淚t is a lovely archaeological breakthrough.鈥�

The lack of evidence for fire-starting had led some researchers to argue that Neanderthals did not know how to ignite fires.

Instead, they suggested that our ancient cousins collected fires from natural sources like wildfires and kept them burning, even carrying them around with them. This idea has now been refuted, Sorensen thinks.

His team think the Neanderthals struck the sparks into tinder fungus mixed with manganese dioxide powder. Tinder听is a common tree fungus that ignites very easily. Team member Marie Soressi showed in 2016 that it ignites even more easily when mixed with powdered manganese dioxide.

Blocks of manganese dioxide have often been found in Neanderthal sites, and she argues they were used for fire-making, rather than as a black pigment as previously thought.

It鈥檚 also possible Neanderthals used other methods of fire-making, such as rubbing sticks together, but wooden tools are seldom preserved.