THE asteroid that killed the dinosaurs was a mere pebble compared with a 30-kilometre rock that clobbered the Earth about 2.5 billion years ago.
Andrew Glikson of the Australian National University in Canberra has found a layer of impact debris spread across the Hamersley Basin of Western Australia. It is less than 20 centimetres thick, but its extent indicates it came from a titanic impact in an ocean basin that hurled droplets of molten rock into the atmosphere. Glikson estimates the crater would have been at least 400 kilometres across.
A 30-kilometre object would have caused a global cataclysm, though…
