A meteorite studded with bits of opal -- a mineraloid that contains properties of water -- discovered in Antarctica is powerful proof the Earth's water originated from asteroids that slammed into the Earth as it was forming billions of years ago.

This is the first time opals have been found on a rock confirmed to have come from an asteroid.

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Scientists have found only one other space rock carrying opal, and this was a meteorite originating from Mars. Opal requires water for it to be formed.

The discovery was announced by Hilary Downes, a geochemist and study lead author at the Birkbeck Institute of Earth and Planetary Sciences at the University of London, during the National Astronomy Meeting held last week in England.

"This is more evidence that meteorites and asteroids can carry large amounts of water ice," said Downes.

"Although we rightly worry about the consequences of the impact of large asteroids, billions of years ago they may have brought the water to the Earth and helped it become the world teeming with life that we live in today."

To reach their conclusion, Downes and her colleagues studied meteorite "EET 83309" consisting of thousands of bits of rocks and minerals, all of which suggest EET 83309 came from the surface of an asteroid.

On the Earth, opal consists of silica commonly found in sand and water. Flowing water picks up sand and other pieces of silica. When the water evaporates, it leaves behind traces of materials that eventually form opals.

Research on EET 83309 by other scientists show the asteroid from which it came was likely hit by other asteroids and meteorites as fragments of other space rocks were discovered on the meteorite. They also said  EET 83309 was exposed to radiation from the sun, solar wind and other cosmic sources.

Since an asteroid lacks an atmosphere to protect it from deadly radiation, the conclusion is the meteorite and the asteroid it came from already had water.

"Our evidence shows that the opal formed before the meteorite was blasted off from the surface of the parent asteroid and sent into space, eventually to land on Earth in Antarctica," said Downes.

Tagsopal, asteroid, EET 83309, Hilary Downes