Biggest-ever extinction linked to asteroid-induced climate change

Economist : Although it is generally accepted that an asteroid impact wiped out the dinosaurs at the end of the Cretaceous period 66 million years ago, it is not known whether the four other mass extinctions that have occurred over the past 540 million years had similar causes. Now Eric Tohver of the University of Western Australia and colleagues propose that the biggest one, which occurred at the end of the Permian period 252.3 million years ago, was also probably caused by an asteroid impact. They point to the Araguainha crater in Brazil. Despite the crater’s relatively small size, some 40 km in diameter, compared with the 180-km-diameter crater associated with the dinosaur extinction, the asteroid impact that created it may have set off a huge geological chain reaction. Tohver’s group theorizes that thousands of earthquakes up to magnitude 9.9 would have resulted, releasing massive quantities of oil and gas from the surrounding oil shale rock. So much atmospheric methane gas would have been released that Earth would have experienced an intense period of global warming. More excavation will be needed, however, to prove the theory.