By Wilson da Silva
THE building blocks of life are increasingly believed to have come from deep space after hitching a ride on the comets that bombarded the earth 4.6 billion years ago.
Scientists at an international astrobiology conference have revealed recent experiments firmed the theory by showing the molecules essential for life appear to have an extraterrestrial origin.
Astronomer Jeremy Bailey of the Anglo-Australian Observatory in NSW said scientists had long known that the 20 amino acids used by all living things were exclusively “left-handed” – a term which refers to their shape – but they had no idea why.
It had been a mystery since French scientist Louis Pasteur first noticed the peculiarity in 1848. Now Dr Bailey believes he has come up with the first explanation, telling the international Bioastronomy 2002 conference meeting on Hamilton Island that this peculiarity could have been caused by exposure to circular polarised light – which has now been discovered in massive gas clouds deep in space.
“We know there’s a large amount of organic material that forms in molecular clouds in space. And we know a lot of this material was present in the early formation of our solar system,” Dr Bailey said.
“But most of it would have been destroyed in the processes that created the planets.”
Which is why some scientists have suggested that the building blocks of life might have travelled on the comets and asteroids that would have routinely bombarded the Earth during its formation.
Dr Bailey explained that the only known way of creating left-handed amino acids is to blast them with circularly polarised light, a destructive form of ultraviolet light that more easily breaks down right-handed amino acids.
But he said there was no known natural source of circularly polarised light on the early Earth.
However, by chance Dr Bailey and his team detected the light in space in interstellar clouds known to be rich in organic molecules.
In addition, recent laboratory experiments by other scientists, presented at the conference, show amino acids blasted with circularly polarised light, also produced an excess of left-handed molecules.
Dr Bailey said, while this was not definitive proof that the building blocks of life came from space, he said it was the strongest explanation so far for this strange left-handed bias in living things.