Article Posted on : - Jan 20, 2011

Asteroids: the carrier of life on Earth?

LONDON (PTI): It’s now official. Life on Earth began in space, says a new study on meteorite strengthening evidence that biological raw ingredients were carried to the planet in lumps of asteroid rocks.

The NASA research has suggested that a wider range of asteroids were capable of creating the kind of amino acids used by life on Earth.

The molecules come in two mirror-image varieties, known as left and right-handed. But only left-handed amino acids are found in nature.

In March 2009, researchers at NASA's Goddard Space Flight Center in Greenbelt found an excess of the left-handed form of the amino acid isovaline in samples of meteorites that came from carbon-rich asteroids.

The discovery suggested that perhaps left-handed life got its start in space, where conditions in asteroids favoured the creation of left-handed amino acids. Meteorite impacts could have supplied this material to Earth.

"This tells us our initial discovery wasn't a fluke; that there really was something going on in the asteroids where these meteorites came from that favours the creation of left-handed amino acids," Dr Daniel Glavin of NASA was quoted as saying by Daily Mail.

The scientists believe that early in its history, Earth was bombarded with meteorites containing left-handed amino acids.

The bias towards left-handedness would have continued as the material was incorporated into emerging life.

Evidence suggests that the presence of liquid water amplifies levels of left-handed isovaline (L-isovaline) in asteroids.

"Liquid water seems to be the key," said Dr Glavin.

"We can tell how much these asteroids were altered by liquid water by analysing the minerals their meteorites contain.

"The more these asteroids were altered, the greater the excess L-isovaline we found. This indicates some process involving liquid water favours the creation of left-handed amino acids."

Radiation may be responsible for initially tipping the balance towards left-handedness, the scientists believe.

Cosmic rays encountered by the solar system in its youth may have led to slightly more left-handed amino acids being created, or slightly more right-handed molecules being destroyed.

Life in other star systems with different early conditions could have built up around right-handed amino acids, said Dr Glavin.

The new findings appear online in the journal Meteoritics and Planetary Science.