Humans could all be aliens

>From Marlowe Hood in Paris

June 14, 2008 04:30am

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 study to be published on Sunday.

European and US scientists have proved for the first time two bits of
genetic coding, called nucleobases, contained in the meteor fragment,
are truly extraterrestrial.

Previous studies had suggested the space rocks, which hit earth about 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.

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, about 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 nucleobases were synthesised closer to home,
but Martins said the atmospheric conditions of early earth would have
rendered that process difficult or impossible.

A team of European and US scientists showed 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.

The study, to be 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 be carried out up to now by other
scientists.
http://www.news.com.au/story/0,23599,23861977-38200,00.html