AN ASTEROID that wiped out huge swathes of life when it collided with Earth 360 million years ago may also have brought with it untapped mineral wealth.
Robert Iasky of Western Australia鈥檚 Department of Mineral and Petroleum Resources (DMPR) discovered the 120-kilometre wide Woodleigh impact crater accidentally as he was drilling for coal near Shark Bay, 650 kilometres north of Perth. When Iasky and his colleagues drilled down into the crater, which is buried under up to 600 metres of rock and sand, they discovered a huge chunk of dense granite that had been dragged upwards as the ground rebounded when the asteroid hit.
Mineralogist Franco Pirajno of the DMPR has now analysed samples of the granite and was surprised to find that it contains valuable elements such as magnesium, copper, chromium and nickel, which is unusual in this kind of rock.
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Instead of the asteroid being vaporised and spread through the air over a wide area, Pirajno concludes that many of its components must have been incorporated into the surrounding hot granite. The rock would have been crushed under pressures of around 100,000 atmospheres. 鈥淚t must have created one hell of a bang,鈥� he says. Gold deposits may also have formed as streams of hot water ran through cracks in the rock.
But although the asteroid may have left behind a valuable legacy for mining companies, its impact at the time would have been devastating. Dating of the rock samples has revealed that the collision happened 360 million years ago-the time of a mass extinction towards the end of the Devonian period, when 85 per cent of all species were wiped out. Geologists have long speculated that an asteroid may have been responsible, but until now there was no known impact that could have triggered the catastrophe.
The Woodleigh asteroid certainly had enough destructive potential-it was about five kilometres wide, making it the fourth largest asteroid collision ever discovered on Earth, almost as big as the Mexican Chicxulub collision that鈥檚 thought to have wiped out the dinosaurs 65 million years ago. The impact would have been felt globally, triggering earthquakes and volcanic activity, as well as creating a cloud of dust that spread around the world, blocking out sunlight.
Iasky believes more craters may lie hidden under Western Australia鈥檚 red deserts and is keen to keep searching. But Pirajno says it is now up to the mining companies to investigate the economic potential of the Woodleigh site.
