Meteorites

Over time Earth's surface has changed dramatically as its dynamic plates reshaped the continents, all but erasing the evidence of the ancient bombardment.

Now researchers have discovered for the first time evidence in rocks, found in Canada and Greenland, that they say confirms Earth was bombarded as heavily as the moon.

The researchers said a form of tungsten found in the rocks, which came from the Earth's early crust, is usually found in meteorites.

There is a chemical fingerprint in the earth's oldest terrestrial rocks of a heavy meteorite bombardment 3800 to 4000 million years ago.

The origin of the meteorites is not fully resolved, but is thought to be material remaining after all the other planets had formed.

The findings may also be relevant to the debate about the earliest signs of life on Earth.

The debate revolves around the origin of tiny graphite particles that have been found in the same ancient rocks. The presence of extraterrestrial tungsten raises the possibility that this graphite could also be of meteoritic origin.

This finding has implications for the origin of life on Earth as these giant impacts would have annihilated any possible existing life-forms but also delivered complex molecules from carbonaceous chondrites, a type of meteorite, to the Earth's surface.