Remnants of two meteorite craters have been identified in central Australia. Each is huge in its own right. If, as suspected, the two originate from the same asteroid, the combined area might be larger than any single crater on the planet, and may have played an important part in the history of evolution.
It might be expected that an impact area 400 kilometers (250 miles) across would have been found long ago, but over millions of years the region has been eroded and filled in to the point where nothing is visible at the surface. The impact sites—around 200 kilometers (125 miles) across each—were only discovered because their location in the Warburton Basin hosts another geological phenomenon of global significance.
The Cooper Basin, which overlaps with the Warburton East Basin, contains the world's greatest resource of hot dry rocks, granites at temperatures around 240°C. Several companies are hoping to use the vast quantity of heat located kilometers beneath the surface by pumping water to depths where it will boil and return to the surface as steam that can produce electricity. Extensive drilling is required to find the best locations and in the process geologists noticed indications of a long buried meteor crater.
Further research has now shown evidence of two matching impacts that are similar in size and depth. In Tectonophysics, a team led by Australian National University's Dr. Andrew Glickson proposes that the Basin's magnetic and gravitational anomalies and shocked quartz are indicative of an asteroid that broke in two prior to impact. The anomalies are the result of material from the Earth's mantle entering the crust, and shocked rocks are a well-established marker of asteroid events.
This could become the second confirmed example of dual impacts after a pair in Sweden. “The two asteroids must each have been over 10 kilometres [6 miles] across,” says Glickson. “It would have been curtains for many life species on the planet at the time.”
Glickson and his co-authors have tried to match the impacts with an extinction event. After all, with craters each wider than the Chicxulub crater that wiped out the dinosaurs, there should be a visible trace in the fossil record. However, the team is hampered by a lack of rocks suitable for isotopic analysis to allow them to place the timing of the impact precisely. Some geologists think the impacts occurred 300 million years ago when some of the granites in the area were formed. Glickson told IFLS he suspects the impacts are older, and are possibly the cause of the Late Devonian mass extinction 366 million years ago.
Glickson also says the impacts may have contributed to the huge geothermal resource that led to their discovery, with the rebound domes caused by the impacts holding magma from the mantle and possibly contributing to the heat that has survived to this day.
The Vredfort crater in South Africa, generally considered the world's largest, has been estimated at 478km (297 miles) wide, but other estimates are a third of this. Even if neither crater on their own would rank as the planet's biggest, Glickson told the ABC that their combination is “the biggest we know of anywhere in the world.”