Life on Earth was almost wiped out twice

Asteroids have almost wiped out life on Earth not once but twice, according to new studies released today.

Asteroids have almost wiped out life on Earth not once but twice, according to new studies released today.

The strike that effectively made dinosaurs extinct 65 million years ago was mild compared to the one which hit the Earth 250 million years ago, scientists say.

The discovery emerged through the detection of carbon molecules called "buckyballs" which only occur naturally in space. The dramatic extinction occurred when an asteroid estimated to have been between four and eight miles across hit the planet at a still unknown location.

That triggered a cataclysm in which volcanoes spewed ash and lava into the atmosphere and plunged the world into centuries of dark and cold. As a result, 90 per cent of all marine creatures and 70 per cent of land vertebrates became extinct. All 15,000 species of trilobites - odd cockroach-like invertebrates which virtually ruled the world - died out.

The mass extinction, whose causes had puzzled scientists for decades, came at the so-called "Permian-Triassic boundary", which marked a sudden change in the number and variety of species. Now, the reason for its existence is clear.

The impact released "an amount of energy basically about one million times [bigger than] the largest earthquake recorded during the last century", said Robert Poreda, associate professor of earth and environmental sciences at the University of Rochester in New York, a co-author of the study, published today in the journal Science. "We're not sure of all the environmental consequences, but with both the impact and with the volcanic activity, we do know that Earth was not a happy place."