A massive impact with a giant asteroid could have kick-started life on Earth more than four billion years ago by providing an ideal environment for incubating the world's first lifeform.

Scientists studying an impact crater in the Arctic have found evidence to suggest that asteroids hitting the Earth can help life to flourish as well as cause catastrophic destruction.

Charles Cockell, of the British Antarctic Survey in Cambridge, said analysis of rocks in the Haughton impact crater on Devon Island, Nunavut Territory, Canada, has shown how asteroids can help life to flourish.

The intense heat of an asteroid impact causes rock minerals to vapourise, leaving tiny cracks and crevices inside the rock where microbes can live.

"We've discovered that rocks inside the crater are more heavily colonised by microbes than the rocks outside the crater," Dr Cockell told the British Association Festival of Science being held in Exeter.

"So what we have here is an example of how impact events can create a habitat for life and not merely act as agents of destruction," he said.

The Haughton crater was created 25 million years ago when an asteroid about a kilometre wide hit Earth, releasing energy equivalent to about 1,000 Hiroshima atomic bombs.

"When they hit the ground most of the energy is released as heat and one of the effects of that is to provide the energy for simple organic compounds to form more complex compounds," Dr Cockell said.

The heat from a similar impact about four billion years ago could have lasted for between 1,000 and a million years. This may have kept any water collecting within the crater at a constant warm temperature, providing an ideal environment for the origins of life.

"It is one of the rare instances where asteroids and comets could actually be good for life," Dr Cockell said.

"There's a growing feeling that as well as being beneficial in terms of habitat, impact events can also improve conditions for the evolution of life in the first place. As well as telling us something about evolution on Earth, these impact craters may be relevant for the search for life elsewhere," he added.

Meanwhile, methane gas has been found on Mars. The only explanation for the gas is undiscovered volcanic activity or primitive underground life, Andrew Coates, a British scientist at the Mullard Space Science Laboratory, told the Festival of Science yesterday.