Wednesday 22 November 2017

Earth and Moon 'bombarded with large asteroids 3.9bn years ago'

Matthew Moore

Any life which may have existed on Earth 3.9bn years ago would have been wiped out in a devastating asteroid strike, new analysis of Moon craters indicates.

Earth and its satellite were bombarded with large asteroids during the solar system’s “turbulent youth”, striking new topographical maps show.

The impacts would have been powerful enough to evaporate any water on our planet and destroy any early organisms.

The scale of the onslaught has been revealed by the most detailed analysis of Moon craters ever carried out by scientists.

A team led by researchers at Brown University in the US used a laser altimeter on board Nasa's Lunar Reconnaissance Orbiter to identify and map a total of 5,185 asteroid craters on the Moon’s surface. All of the craters are at least 20km in diameter.

They found that the largest craters tend to be clustered in regions where the surface of the Moon is older.

In areas where the surface is newer – having been formed by subsequent lava flows – the researchers found the average crater size is significantly smaller.

The evidence supports the view that the Moon and the Earth endured a bombardment of large asteroids around 3.9bn years ago.

This is thought to have come to a halt a few hundred of millions of years later, when Jupiter and Saturn settled into their orbits and began to exert a different gravitational pull on the asteroid belt from where the missiles originated.

Since then, we have generally escaped the largest asteroids hurtling through space.

James W Head III, who led the research published in the journal Science, said that the findings "are telling us something about the infancy of the solar system."

He added: "It is clear we can find out and learn so much more from future missions, robotic or otherwise. There is so much to do."

Scientists are forced to analyse the Moon for clues our planet’s geological history because erosion has destroyed evidence of distant asteroid strikes on Earth.

Earth was formed around 4.5bn years ago. Scientists are uncertain when life first emerged, but evidence indicates that microorganisms existed around 3.5bn years ago.

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