Meteorite gives clue to origins of life on Earth

Astronomers believe they have discovered yet another clue to the origins of life on Earth. Their work adds weight to theories that the chemical building blocks of life were delivered here by impacting comets and meteorites.

At the very least the international team, which was studying the Great Nebula in the Orion constellation, has helped solve a question about human biochemistry that has puzzled scientists for 150 years.

Louis Pasteur in 1848 discovered that some molecules could exist in two mirror-image forms, right-handed or left-handed. This holds true for the molecules that sustain life, the amino acids which join to form proteins and the complex sugars including deoxyribose, a component of DNA.

Organisms on this planet prefer left-handed amino acids and right-handed sugars. No reason could be found for this, and the puzzle was compounded when synthetic copies of these substances were produced in the laboratory and equal numbers of right and left-handed were formed.

The team, including researchers from the University of Hertfordshire and using the Anglo-Australian telescope, have found how this "handedness" which is essential for life could have arisen. Their report appears this morning in the journal, Science.

They found that the new stars - and presumably planets - being formed in the Great Nebula are bathed in "circularly polarised light", a form of light rarely encountered anywhere in the solar system except in a lab.

Scientists working with circularly polarised light in the 1930s discovered it could destroy right-handed amino-acid forms, leaving behind the type found on Earth. But they could find no source for this light which could have influenced life here.

Then scientists at Arizona State University last year discovered an excess of left-handed amino acids when analysing the Murchison meteorite, which fell to Earth in Australia in 1969, a piece of rock that could have been floating in space since the formation of the solar system.

The discovery of circularly polarised light in the Great Nebula helps explain how amino-acid and sugar "handedness" could have arisen. Chemicals clinging to comets and meteorites would have been affected by the polarised light emitted during the Sun's formation long before life could have begun on Earth.

This material could then have been deposited in cataclysmic impacts that are known to have occurred throughout the lifetime of the Earth.

Conditions in the Great Nebula "may well be similar to the region in which our own solar system formed", according to Prof James Hough of the University of Hertfordshire. So the suitability of our planet for life could well have been dictated by the environment in which the Earth formed as much as by conditions on the ground later.