[meteorite-list] Scientist Claims Calculations Prove Life Began in Comet

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu, 16 Aug 2007 15:35:32 -0700 (PDT)
Message-ID: <200708162235.PAA04405_at_zagami.jpl.nasa.gov>

http://www.space.com/scienceastronomy/070816_life_comets.html

Scientist: Calculations Prove Life Began in Comet
By Ker Than
space.com
16 August 2007

Life almost undoubtedly began in space, and specifically in the hearts
of comets, rather than on Earth, a new study claims.

Chandra Wickramasinghe, an astrobiologist at Cardiff University in the
United Kingdom, and his team say their calculations show that it is one
trillion trillion times more likely that life started inside a slushy
comet than on Earth.

"The comets and the warm watery clay pools in comets are settings in
which the organic molecules are transformed into living structures in
comets," Wickramasinghe said. "That transformation is more likely in
some comet somewhere in the galaxy than in any small pond on the Earth."

The new findings will be detailed in an upcoming issue of the
International Journal of Astrobiology.

But while most scientists are willing to concede that fallen comets
might have delivered some of the water and organic materials necessary
for life to Earth, critics say that Wickramasinghe's proposal that life
originated in comets which subsequently crashed on our planet - an idea
called panspermia - is speculative and not supported by evidence.

"It looks to me as if their conclusions are constructed from a series of
speculations, none of which is based on much evidence. It is a theory
built on air, not solidly grounded in scientific facts," said David
Morrison, a senior scientist at the NASA Ames Research Center in Moffett
Field, California, who was not involved in the study.

Speculative

Wickramasinghe and his colleagues' idea rests on the assumption that
comets are full of porous clay particles that can hold water in a liquid
form for eons.
 
Cometary missions such as Deep Impact have found evidence for a variety
of silicates existing inside comets, but not clay per se, Morrison said.

The "assumption that Earth has very little clay while comets are full of
clay is the key to their argument, and it is at best speculation,"
Morrison said.

It is also an open question as to whether comets do indeed contain
liquid water inside them and whether other star systems support comets
at all, let alone clay-, water- or life-bearing comets. "No comets have
been discovered yet around other stars," Morrison said in an email
interview.

Paul Falkowski, a biochemist at Rutgers University in New Jersey, also
does not think that the site of life's origins can be figured out using
simple calculations. "These basic kinds of things are dependent on the
beginning initial assumptions. I don't know that we know the odds,"
Falkowski said. "We know the odds for exactly one planet, and it
happened once, so everything else is a game."

The cosmic ray threat

Recent work by Falkowski and his team suggests that life would have
difficulty surviving unprotected in deep space where comets reside. In
research detailed in the Aug. 6 issue of the journal Proceedings of the
National Academy of Sciences, the team recovered highly degraded
microbial DNA from 8 million-year-old Antarctic ice and estimated that
DNA on Earth has a half-life of only about 1.1 million years. In other
words, every 1.1 million years, half of the DNA disappears.

The researchers say cosmic rays are the culprits and think that DNA-or
any other complex organic molecule-would have a difficult time surviving
for long in space, where radiation levels are much higher than on Earth.

"The radiation flux on the surface of this planet is one-tenth to
one-one-hundredth to that of space," Falkowski told SPACE.com. "So when
you go into a situation where you don't have a magnetic field protecting
you from cosmic background radiation, the amount of damage to DNA would
be incredibly high."

Falkowski's team estimates that DNA would survive only a few hundred
thousand years in space, essentially ruling out interstellar pollination
of life by comets as well as the potential for life to survive in space
for very long.
Received on Thu 16 Aug 2007 06:35:32 PM PDT