[meteorite-list] Genetic Building Blocks May Have Formed in Space (Murchison Meteorite)

[Ron Baalke]

http://space.newscientist.com/article/dn14142-genetic-building-blocks-may-have-formed-in-space.html    

Genetic building blocks may have formed in space
Rachel Courtland
New Scientist
13 June 2008

Some fundamental building blocks of our genetic code might have come
from outer space, according to a controversial new meteorite study.

The study suggests that some organic compounds associated with genetic
material might have formed in a meteorite called Murchison before it
landed in Australia in 1969. The chemicals are two kinds of nucleobases,
ring-like carbon molecules that are essential for the creation of
nucleic acids like DNA and RNA.

The find might bolster claims that meteorites delivered some of the
chemicals needed to create life. "It boosts the idea that the origin of
life on Earth may have had an important contribution from an
extraterrestrial object," says lead author Zita Martins, a chemist at
Imperial College London in the UK.

But it may be too early to conclude these nucleobases formed beyond the
Earth, says Sandra Pizzarello, a chemist at Arizona State University in
Tempe, US. The study "raises a very interesting question that was raised
a very long time ago, but I don't think it solves it", she told New
Scientist.

No one knows how life got its start. Primitive Earth conditions might
not have been favourable
<http://www.newscientist.com/article/mg12617132.600-science-chemical-clues-to-the-origin-of-life-.html>
for the chemistry needed to create life's building blocks.
          
Meteorite impacts

Instead, researchers have argued that frequent bombardments by
meteorites
3.8 billion years ago - when life is suspected to have first emerged -
could have delivered the material to Earth, where it might have helped
further the development of life.

Studies of meteorites, as well as astronomical observations of
interstellar dust and gas, have turned up a number of organic compounds,
including sugars and phosphates.

But nucleobases are also needed to make a nucleic acid like DNA or RNA.
Such chemicals have been found in a number of meteorites, but no one was
sure whether they were extraterrestrial in origin or the result of
earthly contamination.

Noisy signal

To study the origins of these nucleobases, Martins and colleagues
studied the mass of organic chemicals isolated from the meteorite.

The team looked at two different isotopes of carbon in the chemicals,
which included the nucleobases uracil and xanthine. The lighter version,
carbon-12, is present on Earth in large amounts. Carbon-13 is more
common in sweeping clouds of cold, interstellar gas. Large amounts of
the stuff usually indicate the material did not form on Earth.

The ratio of carbon-13 to carbon-12 was unusually high in the two
nucleobases, leading the team to conclude the materials likely formed in
the meteorite itself rather than on Earth.

But Pizzarello says too many other chemicals were present in the samples
to clearly distinguish the carbon ratio. "Analytically, it's not
convincing," Pizzarello told New Scientist.

Astrobiology - Learn more in our out-of-this-world special report
<http://www.newscientistspace.com/channel/astronomy/astrobiology>.

Journal reference: Earth and Planetary Science Letters
<http://www.sciencedirect.com/science/journal/0012821X> (vol 270, p 130)