Some of the molecules synthesised in our experiment have a biologically active nature

Professor Lubomir Gabla Jagiellonian University

A Polish team says it has shown in the laboratory that a biological molecule is formed when space dust is zapped with a high-energy beam of light.

But other scientists are sceptical about claims that life arrived on this planet from outer space.

Thousands of tonnes of dust from space enter the Earth's atmosphere each year.

Open question

The astrophysicists, based at Jagiellonian University, say precursors of life are more likely to have reached Earth in the form of dust than during a comet impact.

The thing to do is go out in space and have a look

Dr Mark Burchell University of Kent at Canterbury

Dust would be more likely to enter the Earth's atmosphere without burning up, they argue, while any complex biological molecules borne by comet would be destroyed.

"The formation of terrestrial life is still an open question. It is believed that abiotic creation of simple biogenic molecules and then later chemical and physical transformation could lead to the generation of cells and then contemporary organisms," Professor Lubomir Gabla of Jagiellonian University told the BBC.

"Some of the molecules synthesised in our experiment have a biologically active nature," he said.

Space missions

Mark Burchell of the Physics laboratory at the University of Kent at Canterbury, UK, says that space missions take scientists closer to answering the question of how life began on Earth.

"The problem in the laboratory is that you always can do things on a bench top," he told BBC News Online.

"But did it really happen? If you think that you could have generated some of these building blocks out in space, the thing to do is go out in space and have a look," he said.

Genesis probe

Nasa launched the Genesis mission two weeks ago: an unmanned mission to collect solar winds and dust.

Its Genesis spacecraft will travel a million miles towards the Sun, open a lid and expose a series of arrays ready to pick up solar wind particles.

After three years the lid will close and the craft will return to Earth with about 20 micrograms of solar wind.

It is estimated that around 3,000 tons of interplanetary dust fall to Earth every year.

The Polish research is published in the journal Physical Review Letters.