Meteorite yields life origin clue

Scientists say that "bubbles" like those in the Tagish Lake meteorite may have helped along chemical processes important for the emergence of life.

The globules could also be older than our Solar System - their chemistry suggests they formed at about -260C, near "absolute zero".

Details of the work by Nasa scientists are published in the journal Science.

Analysis of the bubbles shows they arrived on Earth in the meteorite and are not terrestrial contaminants.

These hollow spheres could have provided a protective envelope for the raw organic molecules needed for life.

Dr Lindsay Keller of Nasa's Johnson Space Center (JSC) in Houston, Texas, told BBC News that some scientists believed such structures were "a step in the right direction" to making a cell wall.

But he emphasised that the globules in Tagish Lake were in no way equivalent to a cell. The hollow spheres seem to be empty, but they do have organic molecules on their surfaces.

Mike Zolensky, a Nasa mineralogist, commented: "If, as we suspect, this type of meteorite has been falling on to Earth throughout its entire history, then the Earth was seeded with these organic globules at the same time life was first forming here."

Co-author Keiko Nakamura-Messenger of JSC told BBC News: "We reported only 26 globules in this paper, because they are small and hard to analyse. But we have seen hundreds in a small area. We can estimate that there are billions of them in this meteorite."

The ratios of different forms, or isotopes, of the elements hydrogen and nitrogen in the meteorite are very unusual, which suggests the structures did not come from Earth, say the scientists.

"The isotopic ratios in these globules show that they formed at temperatures of about -260C, near absolute zero," said co-author Scott Messenger, also from Johnson Space Center.

"The organic molecules most likely originated in the cold molecular cloud that gave birth to our Solar System, or at the outermost reaches of the early Solar System."

The Tagish Lake meteorite was collected immediately after its fall over Canada in 2000. It has been maintained in a frozen state, minimising the potential for terrestrial contamination.

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