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13 September 2003

Shocked into life

STANDING at ground zero in the centre of Haughton crater, it is difficult to grasp the enormity of what occurred here 23 million years ago. Today, Devon Island in the Canadian High Arctic is a polar desert with hardly any plant or animal life. But 23 million years ago, it was a very different place. Lush forests grew, giant rabbits hopped around, and small rhinoceros grazed.

All this changed when a comet or asteroid more than a kilometre wide slammed into the forest. The impact excavated between 70 and 100 billion tonnes of rock, forming a crater 24 kilometres wide. In the blink of an eye, all life in an area only a little smaller than Scotland ended. Plants, animals, rock and soil at the point of impact were vaporised. Further away from the crater, the shock wave, air blast and heat produced finished off most other living things.

But not for good. A few millennia after the impact, Haughton was teeming with life again. The warmth of the impact heated groundwater, creating hydrothermal systems, perfect homes for intrepid colonising organisms, such as bacteria and algae. As the crater cooled, a lake formed and sediments began to accumulate. Thanks to fossils in these sediments, we now know it was gradual climate change, not the asteroid impact, that turned Haughton back into the polar desert we see today.

Geologists are telling similar stories about other sites. Impact craters still deserve their reputations as scenes of devastation, but as they cool, they become ideal spots for life to re-emerge. And this has led some people to wonder if impact …

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