[meteorite-list] Carbon globules in meteorite may have seeded Earth life

[Darren Garrison]

Carbon globules in meteorite may have seeded Earth life

    * 19:00 30 November 2006
    * NewScientist.com news service
    * David Shiga


Life on Earth may have started with the help of tiny hollow spheres that formed
in the cold depths of space, a new study suggests. The analysis of carbon
bubbles found in a meteorite shows they are not Earth contaminants and must have
formed in temperatures near absolute zero.

The bubbles, called globules, were discovered in 2002 in pieces of a meteorite
that had landed on the frozen surface of Tagish Lake in British Columbia,
Canada, in 2000 (see Hydrocarbon bubbles discovered in meteorite).

Although the meteorite is a fragile type called a carbonaceous chondrite, many
pieces of it have been remarkably well preserved because they were collected as
early as a week after landing on Earth, so did not have much time to weather.

Researchers were excited to find the globules because they could have provided
the raw organic chemicals needed for life as well as protective pockets to
foster early organisms.

But despite the relatively pristine nature of the meteorite fragments, there was
no proof that the globules were originally present in the meteorite, and were
not the result of Earthly contamination.

Now, analysis of atomic isotopes shows that the globules could not have come
from Earth and must have formed in very cold conditions, possibly before the Sun
was born. The research was led by Keiko Nakamura-Messenger of NASA's Johnson
Space Center in Houston, Texas, US.
Cold gas cloud

The globules are enriched in heavy forms of hydrogen and nitrogen, called
deuterium and nitrogen-15, respectively, ruling out their formation on Earth.
The relative amounts of these isotopes is characteristic of formation in a very
cold environment: between 10 and 20 Kelvin above absolute zero.

This means that the globules may predate our Sun, since temperatures like these
would have prevailed in the cold cloud of gas from which our Sun formed and
ignited. Alternatively, the globules might have formed after the Sun but while
the planets were still developing.

The right temperatures would also have existed in the outer reaches of the
developing solar system where the comets are thought to have formed.
Intriguingly, comets are known to contain particles of organic material of
roughly the same size, although the shape of these particles is not known.
Membrane-like structures

Either way, the globules are extremely old, says team member Scott Messenger,
also of the Johnson Space Center. "We're looking at the original structures of
organic objects that formed long before the Earth formed," he told New
Scientist.

Nakamura-Messenger's team says the globules could have been important for the
origin of life by providing the raw materials and membrane-like structures
needed. Some scientists think that the presence of some sort of container that
could separate an organism's internal chemistry from its environment was a
crucial stage in the evolution of life.

"It's sort of reminiscent of membrane type structures," agrees Larry Nittler, at
the Carnegie Institution of Washington in Washington DC, US. But as for whether
the structures could have kick-started life on Earth, "I think that’s highly
speculative at this point," he says.

Journal reference: Science (vol 314, p 1439)