[ExI] Alien origin for life on Earth?

[Damien Broderick]

<http://www.cosmosmagazine.com/news/2047/alien-origin-life-earth>

Agençe France-Presse
[]


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.

Alien carbon

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.