mass extinction
Huge asteroids battered Earth about 4.5 billion years agoCreative Commons

Early on in our planet's formation, hell on earth was a reality, with asteroids causing "episodes of complete sterilisation" of the planet.

Published in the journal Nature, researchers from the Southwest Research Institute in Boulder, Colorado, used a computer model to work out how many asteroids pummelled Earth early on in its history.

During the first 500 million years of Earth's life, about 4.5 billion years ago, it was hit by at least four giant asteroids that could have killed off everything and completely resurfaced the planet.

"It was thought that because of these asteroids and comets flying around colliding with Earth, conditions on early Earth may have been hellish," lead author Simone Marchi told LiveScience.

Nature magazine reports that the researchers were able to estimate the volume of asteroids that hit the Earth and Moon by measuring elements including gold and osmium in their crusts.

Had these elements been present before the Moon and Earth split, they would have sunk to their cores, meaning the elements must have been delivered through asteroid impacts.

The study suggests the biggest asteroid to hit Earth would have been 3,000km across, with several more measuring 1,000km. Up to seven asteroids would have been up to 500km wide.

These asteroids would have vaporised all the planet's oceans: "At 1,000 kilometres, the effects would be so wide the planet would probably be completely resurfaced with material from the mantle," Marchi said, adding it would have resulted in "episodes of complete sterilisation of Earth".

According to the authors, the only thing that could have survived was heat-resistant bacteria.

Commenting on the study, Henry Melosh, a geophysicist at Purdue University in West Lafayette, Indiana, said: "This paper shows the way for what will probably become a new thread in research on the environment and geology of the early Earth."