[meteorite-list] Tough Earth Bug May Be From Mars

From: Robert Verish <bolidechaser_at_meteoritecentral.com>
Date: Thu Apr 22 10:08:32 2004
Message-ID: <20020926022624.58739.qmail_at_web80301.mail.yahoo.com>

I think the obvious explanation is that the
proto-microbe was blasted off of Earth and landed on
Mars, where it flourished to become the
radiation-resistant strain, where, in turn, it was
blasted off of Mars only to land back on Earth!!!
;-))))

Okay!! So it's not the simplest explanation. But...

Just think of all the "frequent flyer mileage" this
little microbe has accumulated!
;-)
Bob V.

----------- Original Message ------------
meteorite-list] Tough Earth Bug May Be From Mars
Ron Baalke baalke_at_zagami.jpl.nasa.gov
Wed, 25 Sep 2002 16:42:27 -0700 (PDT)

------------------------------------------------------

http://www.newscientist.com/news/news.jsp?id=ns99992844

Tough Earth bug may be from Mars
Stuart Clark
New Scientist
September 25, 2002

A hardy microbe that can withstand huge doses of
radiation could have evolved this ability on Mars.

That is the conclusion of Russian scientists who say
it would take far longer than life has existed here
for the bug to evolve that ability in Earth's clement
conditions. They suggest the harsher environment of
Mars makes it a more likely birthplace.

The hardy bugs could have travelled to Earth on pieces
of rock that were blasted into space by an impacting
asteroid and fell to Earth as meteorites.

Deinococcus radiodurans is renowned for its resistance
to radiation - it can survive several thousand times
the lethal dose for humans. To investigate how the
trait might have evolved, Anatoli Pavlov and his
colleagues from the Ioffe Physico-Technical Institute
in St Petersburg tried to induce it in E. coli.

99.9 per cent deadly

They blasted the bugs with enough gamma rays to kill
99.9 per cent of them,
let the survivors recover, and then repeated the
process. During the first
cycle just a hundredth of the lethal human dose was
enough to wipe out 99.9
per cent of the bacteria, but after 44 cycles it took
50 times that initial
level to kill the same proportion.

However, the researchers calculate that it would take
thousands of such
cycles before the E. coli were as hardy as
Deinococcus. And on Earth it
would take between a million and a hundred million
years to accumulate each
dose, during which time the bugs would have to be
dormant.

Since life originated on Earth about 3.8 billion years
ago, Pavlov does not
believe that there has been enough time for this
resistance to evolve.

Dormant bugs

On Mars, however, the researchers calculate that
dormant bugs could receive
the necessary dose in just a few hundred thousand
years, because radiation
levels there are much higher.

What is more, they point out that the Red Planet
wobbles on its rotation
axis, producing a regular cycle of climate swings that
would drive bacteria
into dormancy for long enough to accumulate such
doses, before higher
temperatures enabled the survivors to recover and
multiply. Pavlov reported
the results last week at the Second European Workshop
on Astrobiology in
Graz, Austria.

David Morrison of NASA's Astrobiology Institute is
sceptical that
Deinococcus came from Mars, pointing out that its
genome looks similar to
those of other Earthly bacteria. But he admits that
there's still no obvious
explanation for the bug's resistance to radiation.

"It is certainly a mystery how this trait has
developed and why it persists," he says.





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Received on Wed 25 Sep 2002 10:26:24 PM PDT