Extraterrestrial Enigma: Missing Amino Acids In Meteorites

http://www.geosociety.org/news/pr/03-37.htm

The Geological Society of America News Release
Contact: Contact: Ann Cairns
Phone: 303-357-1056; Fax: 303-357-1074


HOLD FOR EMBARGO
MONDAY, NOVEMBER 3, 12:00 A.M., EST

Extraterrestrial Enigma: Missing Amino Acids In Meteorites

Amino acids have been found in interstellar clouds and in meteorites - but
with some enigmatic omissions and tantalizing similarities to life on Earth.
Just why some amino acids are present in meteorites and others are absent,
and why they seem to prefer the same "left-handed" molecular structure as
Earth's living amino acids are questions that could unravel one of the most
fundamental questions of science: Where and how did life begin?

"The bottom line is that you have these materials that come from space,"
says Steve Macko, professor of environmental sciences at the University of
Virginia in Charlottesville. Macko refers specifically to eight of the amino
acids found in a certain kind of meteorite - a carbonaceous chondrite. All
eight amino acids are identical to those used by life on Earth. That could
seem to point to a cosmic origin of these basic biological building blocks,
says Macko. The case is bolstered by the fact that early Earth was bombarded
with meteorites and the amino acid glycine has been detected on interstellar
molecular clouds.

The implications and enigmas of extraterrestrial amino acids will be
detailed at a special session celebrating the life and work of the late
Glenn Goodfriend, on Monday, Nov. 3, 2003, at the annual meeting of the
Geological Society of America in Seattle, WA.

Making the case for cosmic origins of Earth's amino acids even more
compelling is the fact that all of the meteorite amino acids, except
glycine, favor the "left-handed" molecular structure, or chirality, that is
also favored by life on Earth. The preference for left-handed amino acids
was a necessary precondition for life, but just why life chose left (L-amino
acids) over right (D-amino acids) is a mystery.

"Essentially all of your protein is made of L-amino acids," said Macko. "Why
is that? We don't know. The curious thing is that if you go to a meteorite
you find a predominance of the same thing."

Another unanswered question: Why have only eight of life's 20 amino acids
been found in meteorites? Perhaps all the amino acids were there, but
something about the history of the meteorites or the analytical processes
used limited their presence or their detection, Macko speculates.

Only in recent years has the idea of amino acids from space affecting the
start of life on Earth become a plausible hypothesis, explains Macko.
Initially, amino acids were thought to have been created in the primordial
atmosphere of early Earth. In a now famous experiment more than a
half-century ago, Stanley Miller and Harold Urey showed that amino acids
were synthesized by simply creating lightning-like electrical discharges
through a fog of water, methane and ammonia - all of which were thought to
be readily available in Earth's early years. The experiment was proof that
amino acids, out of which all life's proteins are made, can be created by
strictly physical-chemical processes, without the help of living organisms.

Perhaps the most famous carbonaceous chondrite was the Murchison meteorite,
which fragmented and fell in 1969 in and around the small town of Murchison,
Victoria, about 70 miles north of Melbourne, Australia. Amino acids and
other organic molecules were found in the Murchison meteorite. The mix of
amino acids found in the Murchison Meteorite was similar to those produced
in Miller-Urey type experiments. A chief difference, however, was seen by
Mike Engel in his PhD research: Unlike the Miller-Urey experiment which
produced equal amounts of the D and L- amino acids, Murchison tended to have
l-amino acids predominate. The fact that the meteorite was seen falling and
fragments were collected quickly minimized the chances that they were
contaminated by Earth amino acids.

The Miller-Urey experiment, combined with the discovery of amino acids in
carbonaceous chondrites and the detection of glycine in molecular clouds,
raise compelling issues about the origin of life on Earth, and its possible
existence elsewhere in the solar system and beyond.

The Significance of Protein Amino Acids in Carbonaceous Meteorites
Monday, November 3, 5:15 p.m., WSCTC: 606
Abstract may be viewed at:
gsa.confex.com/gsa/2003AM/finalprogram/abstract_59831.htm

CONTACT INFORMATION

Steve Macko
434-924-6849


Michael Engel


During the GSA Annual Meeting, Nov. 2-5, contact Ann Cairns at the GSA
Newsroom, Washington State Convention Center and Trade Center, Seattle, for
assistance and to arrange for interviews: 206-219-4615.

On 3 Nov 2003 17:49:23 GMT, (Ron Baalke)
wrote:

A chief difference, however, was seen by
Mike Engel in his PhD research: Unlike the Miller-Urey experiment which
produced equal amounts of the D and L- amino acids, Murchison tended to have
l-amino acids predominate. The fact that the meteorite was seen falling and
fragments were collected quickly minimized the chances that they were
contaminated by Earth amino acids.

Is it possible the meteorite amino acids could be of exobiological
origin?

The scenario I'm thinking of involves the asteroid belt, and the
material that failed to form a planet. I don't know what was the
largest object that's ever existed in the asteroid belt, but I've seen
one source suggest that about 8 Mars-sized objects might have formed,
before Jupiter's gravity perturbed their orbits enough that they
scattered out of the belt or collided with each other at high enough
velocity to disintegrate. (This idea, if correct, would account for
the differentiation of meteorites into iron, stone and carbonaceous
chondrites.)

Now, a Mars-sized object can retain air, water and volcanic heat for a
significant length of time. We don't know how long it took life to
evolve; perhaps only a few million years. Could some of these objects
have remained in stable orbits long enough for life to have evolved
and spread before they were destroyed in collisions? Then the chiral
amino acids might be the remains of life from primordial
proto-planets.

Of course, the above is fairly wild speculation, but I'm curious - is
there a chance it could be correct?

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