[ExI] Alien origin for life on Earth?
thespike at satx.rr.com
Mon Jun 16 05:04:52 UTC 2008
PARIS: Genetic material from outer space found in
a meteorite in Australia may well have played a
key role in the origin of life on Earth,
according to a new international study.
European and U.S. scientists have proved for the
first time that two bits of genetic coding,
called nucleobases, contained in the meteor
fragment, are truly extraterrestrial.
Previous studies had suggested that the space
rocks, which hit Earth some 40 years ago, might
have been contaminated upon impact. Both of the
molecules identified, uracil and xanthine, "are
present in our DNA and RNA," said lead author
Zita Martins, a researcher at Imperial College,
London. [this is misleading; see below]
RNA, or ribonucleic acid, is another key part of
the genetic coding that makes up our bodies.
These molecules would also have been essential to
the still-mysterious alchemy that somehow gave
rise, some four billion years ago, to life itself.
"We know that meteorites very similar to the
Murchison meteorite, which is the one we
analysed, were delivering the building blocks of
life to Earth 3.8 to 4.5 billion years ago," Martins said.
Competing theories suggest that nucleobases were
synthesised closer to home, but Martins counters
that the atmospheric conditions of early Earth
would have rendered that process difficult or impossible.
A team of European and U.S. scientists showed
that the two types of molecules in the Australian
meteorite contained a heavy form of carbon
carbon 13 which could only have been formed in space.
"We believe early life may have adopted
nucleobases from meteoric fragments for use in
genetic coding, enabling them to pass on their
successful features to subsequent generations," Martins said.
If so, this would have been the start of an
evolutionary process leading over billions of
years to all the flora and fauna including human beings in existence today.
Are we alone?
The study, published in Earth Planetary Science
Letters, also has implications for life on other planets.
"Because meteorites represent leftover materials
from the formation of the solar system, the key
components of life including nucleobases
could be widespread in the cosmos," said
co-author Mark Sephton, also at Imperial College, London.
"As more and more of life's raw materials are
discovered in objects from space, the possibility
of life springing forth wherever the right
chemistry is present becomes more likely," he said.
Uracil is an organic compound found in RNA, where
it binds in a genetic base pair with another
molecule, adenine. Xanthine is not directly part
of RNA or DNA, but participates in a series of
chemical reactions inside the RNA of cells.
The two types of nucleobases and the ratio of
light-to-heavy carbon molecules were identified
through gas chromatography and mass spectrometry,
technologies that were not available during
earlier analyses of the now-famous meteorite.
Even so, said Martins, the process was extremely
laborious and time-consuming one reason it had
not previously been carried out by other scientists.
More information about the extropy-chat