Far from wiping out life on earth, heavy meteorite bombardment four billion years ago could have given a boost to the microbes that were our ancestors, new research has found.
Simple organisms could have evaded meteorite bombardment by living underground and reinvading surface rock whilst it was still hot.
The discovery could give scientists new clues about early life on Mars.
"Similar meteorite craters with similar minerals occur on Mars, and this work highlights an approach that could help us look for evidence of life there," says John Parnell, professor in geology at the University of Aberdeen.
It had been believed that life on Earth couldn't have survived the bombardment, and that several cycles of evolution might have taken place before simple organisms finally got a permanent hold.
But studies of a type of ancient microbe — thought to be amongst the earliest to inhabit Earth — have revealed for the first time that primitive life could have hung on.
Experts from the University of Aberdeen and the Scottish Universities Environmental Research Centre collected and analysed mineral samples from the Haughton Crater on Devon Island, an uninhabited island in the Canadian High Arctic.
They found that minerals in the crater had been deposited by a type of microbe which likes heat, and can cope with temperatures close to boiling point.
The microbes had colonised the whole crater - over 20km across and at least 200 metres below the Earth’s surface — indicating that they would have been able to live deep underground in the darkness known as the ‘deep biosphere’.
"Our analysis of the mineral told us that this ancient microbe could have been able to survive meteorite bombardment through a combination of living underground and reinvading the surface rock while it was still very hot," says Parnell.
“Our findings add to a growing body of evidence that there is much life on our planet that lives deep below out of sight and that this is where early life on Earth may have started."
The research is published in Geology.