Article: Primordial Soup's On - Scientists Repeat Evolution's Most Famous Experiment
Robert Karl Stonjek
Their results could change the way we imagine life arose on early Earth
By Douglas Fox
A Frankensteinesque contraption of glass bulbs and crackling electrodes has
produced yet another revelation about the origin of life.
The results suggest that Earth's early atmosphere could have produced
chemicals necessary for life-contradicting the view that life's building
blocks had to come from comets and meteors. "Maybe we're over-optimistic,
but I think this is a paradigm shift," says chemist Jeffrey Bada, whose team
performed the experiment at the Scripps Institution of Oceanography in La
Jolla, Calif.
Bada was revisiting the famous experiment first done by his mentor, chemist
Stanley Miller, at the University of Chicago in 1953. Miller, along with his
colleague Harold Urey, used a sparking device to mimic a lightning storm on
early Earth. Their experiment produced a brown broth rich in amino acids,
the building blocks of proteins. The disclosure made the pages of national
magazines and showed that theories about the origin of life could actually
be tested in the laboratory.
But the Miller-Urey results were later questioned: It turns out that the
gases he used (a reactive mixture of methane and ammonia) did not exist in
large amounts on early Earth. Scientists now believe the primeval atmosphere
contained an inert mix of carbon dioxide and nitrogen-a change that made a
world of difference.
When Miller repeated the experiment using the correct combo in 1983, the
brown broth failed to materialize. Instead, the mix created a colorless
brew, containing few amino acids. It seemed to refute a long-cherished icon
of evolution-and creationists quickly seized on it as supposed evidence of
evolution's wobbly foundations.
But Bada's repeat of the experiment-armed with a new insight-seems likely to
turn the tables once again.
Bada discovered that the reactions were producing chemicals called nitrites,
which destroy amino acids as quickly as they form. They were also turning
the water acidic-which prevents amino acids from forming. Yet primitive
Earth would have contained iron and carbonate minerals that neutralized
nitrites and acids. So Bada added chemicals to the experiment to duplicate
these functions. When he reran it, he still got the same watery liquid as
Miller did in 1983, but this time it was chock-full of amino acids. Bada
presented his results this week at the American Chemical Society annual
meeting in Chicago.
"It's important work," says Christopher McKay, a planetary scientist at NASA
Ames Research Center in Moffett Field, Calif. "This is a move toward more
realism in terms of what the conditions were on early Earth."
Most researchers believe that the origin of life depended heavily on
chemicals delivered to Earth by comets and meteorites. But if the new work
holds up, it could tilt that equation, says Christopher Chyba, an
astrobiologist at Princeton University. "That would be a terrific result for
understanding the origin of life," he says, "and for understanding the
prospects for life elsewhere."
But James Ferris, a prebiotic chemist at Rensselaer Polytechnic Institute in
Troy, N.Y., doubts that atmospheric electricity could have been the only
source of organic molecules. "You get a fair amount of amino acids," he
says. "What you don't get are things like building blocks of nucleic acids."
Meteors, comets or primordial ponds of hydrogen cyanide would still need to
provide those molecules.
Bada's experiment could also have implications for life on Mars, because the
Red Planet may have been swaddled in nitrogen and carbon dioxide early in
its life. Bada intends to test this extrapolation by doing experiments with
lower-pressure mixes of those gases.
Chyba is cautious: "We don't know," he says, "whether Mars really ever had
that atmosphere." That's because Mars today has carbon dioxide, but hardly
any nitrogen-which is also needed for making amino acids. Some scientists
suspect that nitrogen gas existed on Mars, but was blasted away by asteroid
impacts billions of years ago.
Source: Scientific American
http://sciam.com/article.cfm?chanID=sa004&articleID=9952573C-E7F2-99DF-32F2928046329479
Posted by
Robert Karl Stonjek
Perplexed in Peoria
"Robert Karl Stonjek" <rsto...@bigpond.net.au> wrote in message news:ev3d6b$uc$1...@darwin.ediacara.org...
> Primordial Soup's On: Scientists Repeat Evolution's Most Famous Experiment
> Their results could change the way we imagine life arose on early Earth
> By Douglas Fox
>
>
> Source: Scientific American
> http://sciam.com/article.cfm?chanID=sa004&articleID=9952573C-E7F2-99DF-32F2928046329479
Thanks RKS, and also TH, for calling our attention to this article. But there
is almost no information here as to what was different and how much difference
it made. Nothing about it on Bada's or Scripps's web pages either. Even NASA's
astrobiology site doesn't have it. If anyone can post more information about this
one, I would appreciate it.
DK
The paper is not published yet. The abstract as submitted is:
*************
Prebiotic organic synthesis in neutral planetary atmospheres
Jeffrey L. Bada, jb...@ucsd.edu1, Jim Cleaves, hcle...@ucsd.edu2,
John H. Chalmers2, and Antonio Lazcano3. (1) Scripps Institution of
Oceanography, University of California at San Diego, La Jolla, CA 92093-0212,
(2) Scripps Institution of Oceanography, La Jolla, CA 92093-0212, (3) Facultad
de Ciencias, UNAM, Mexico D.F, 04510, Mexico
A reservoir of organic compounds, supplied by either endogenous or
exogenous sources, is thought to be necessary for the origin of life. It
has been demonstrated that the action of an electric discharge on
reduced gas mixtures such as H2O, CH4 and NH3 (or N2) results in the
production of copious amounts of several biologically important organic
compounds such as amino acids. However, it is now widely held that the
early Earth's atmosphere was likely neutral, dominated by N2 and CO2.
The synthesis of organic compounds by the action of electric discharges
on neutral gas mixtures has been shown to be much less efficient. However,
we show here that contrary to previous findings, significant amounts of amino
acids are produced under these conditions. The low yields found previously
were the result of oxidation of the organic compounds during hydrolytic workup
by nitrite and nitrate produced in the reactions. Addition of oxidation inhibitors
prior to hydrolysis results in the recovery of several hundred times more amino
acids than reported previously. Organic synthesis from neutral atmospheres
may thus have depended as much on oceanic conditions as on the
characteristics of the primitive atmosphere itself. These findings imply the
need for a critical re-evaluation of the importance of such syntheses on the
primitive Earth and other planetary bodies, such as Mars, that may have been
endowed with CO2 and N2-rich atmospheres throughout a major part of their
history.
***********
>From the description of it, it would seem to imply that wet red clay
might just be what doctor ordered.
DK
Tim Tyler
> Prebiotic organic synthesis in neutral planetary atmospheres
>
> Jeffrey L. Bada, jb...@ucsd.edu1, Jim Cleaves, hcle...@ucsd.edu2,
> John H. Chalmers2, and Antonio Lazcano3. (1) Scripps Institution of
> Oceanography, University of California at San Diego, La Jolla, CA 92093-0212,
> (2) Scripps Institution of Oceanography, La Jolla, CA 92093-0212, (3) Facultad
> de Ciencias, UNAM, Mexico D.F, 04510, Mexico
>
> A reservoir of organic compounds, supplied by either endogenous or
> exogenous sources, is thought to be necessary for the origin of life.
[...]
Organic compounds, are thought to be necessary for the origin of life -
by /some/ researchers.
Others point out that the tendency of organic compounds to form
sticky tars that hinder the self-organizing process of crystal
formation - which is most likely key to the origin of life -
means that the most probable role of organic compounds in the
origin involved them gumming up the works.
Most carbon-based compounds are typically too reactive, and too likely
to engage in irreversible chemical reactions that hinder self assembly.
The chemicals which self assemble best are less reactive and more
inert - and thus more likely to engage in the near-reversible reactions
which facilitate http://originoflife.net/error_correction/
These tend to be are based on silicon or metal elements.
http://originoflife.net/cairns_smith/
Organic compounds were important later on. They were
most likely synthesized by existing organisms, so the
significance of the catalytic effect of lighning on
hypothetical primitive atmospheres is much reduced.
--
__________
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