Volcanic origin of proteins?
The reanalysis of a 1958 experiment suggests that volcanic eruptions may have spawned the amino acids that contributed to the rise of life on earth
Scientific debates don't get much hotter than the one surrounding the origin of organic molecules at the dawn of life on Earth. New findings, based on a reanalysis of a 50-year-old experiment, suggests that ancient volcanic activity was the source of the very first amino acids.
The linkurl:findings,;http://www.pnas.org/content/early/2011/03/14/1019191108.abstract published open access today (March 21) in the Proceedings of the National Academy of Sciences, lend support to the theory that the building blocks of organic life spewed from volcanoes billions of years ago.
"Volcanic discharges could have been important in forming pre-organic molecules, which is consistent with this experiment," said volcanologist linkurl:Clive Oppenheimer;http://www.geog.cam.ac.uk/people/oppenheimer/ of the University of Cambridge, who was not involved with the study. "And it's a nice piece of science revisiting itself."
In the 1950s, Stanley Miller and Harold Urey of the University of Chicago performed a series of "spark discharge" experiments, in which the researchers applied electrical sparks-- meant to simulate lightning -- to a mixture of gases in steam-filled flasks. As the heat inside the flasks rose and the sparks flew, solids were produced and were captured in vials that could be stored for later analysis. Amino acids were formed in these reactions and they provided support for Miller's hypothesis that organic molecules could be formed from inorganic gases.
When Miller died in 2007, he left his entire lab to his second graduate student linkurl:Jeffrey Bada,;http://www.sio.ucsd.edu/Profile/jbada who is now a marine chemist at the Scripps Institution of Oceanography. Among this collection was a small cardboard box with the words "spark discharge" scrawled on its side. Inside the box were some of those vials from the 1950s experiments containing solid product, some of it unanalyzed.
"It's like someone had hit me over the head with a bat," said Bada of the find. "I was just flabbergasted that he had never mentioned it."
Out of this collection, Bada selected two vials for analysis: one, the result of Miller's original 1953 experiment, which Bada analyzed for a 2008 linkurl:publication,;http://www.sciencemag.org/content/322/5900/404/suppl/DC2 and a second, the first of few experiments Miller performed using sulfur gas. In this experiment, conducted in 1958, Miller mixed hydrogen sulfide with carbon dioxide, ammonia and methane -- a combination that Bada recognized as representing the gaseous makeup of a volcanic plume, in which reducing gases from the volcano interact with neutral or oxidizing atmospheric gases.
"Volcanism was probably more prevalent in early earth," said Oppenheimer. "There was a hotter mantle, and the planet's bombardment by meteorites in itself generates a lot of volcanism."
The experiment's combination of gases is also similar to the chemical mixture issuing from hydrothermal vents and analyzing the results could lend support to the hypothesis that both volcanoes and vents are the cradles of life.
When Bada and his colleagues analyzed the product from Miller's 1958 vial, they found 23 different amino acids -- more than had ever before been produced from inorganic components -- a quarter of which contained sulfur from the simulated volcanic plume. "One of the most striking things you get out of that experiment is that hydrogen sulfide enriches the abundance and diversity of amino acids" compared to experiments that don't contain sulfur, Bada said.
But the composition of the early atmosphere is a controversial subject, and not everyone is convinced that the conditions of the 50-year old experiment are representative of young Earth. Most of the evidence for early atmospheric composition is fossil based -- identifying the oxidation state of minerals, for example, or looking at fossil soils -- with no direct samples, so "most of the inferences are made indirectly," said Oppenheimer.
|Lightning struck during the eruption of Mount Rinjani in Indonesia in 1995|
Image: Wikimedia Commons, Oliver Spalt
Download Flash player to listen to an astrobiologist's take on the study
Astrobiologist David Grinspoon of the Denver Museum of Nature and Science
describes the opposing ideas about the early atmosphere and why
these experiments are still meaningful.
"It's almost impossible that the early atmosphere looked like that," said planetary scientist linkurl:Jim Kasting;http://www.geosc.psu.edu/people/faculty/personalpages/jkasting/index.html of Pennsylvania State University, who did not participate in the research. Plus, he argued, over the past 20 years, many scientists have begun to argue that RNA molecules, not amino acids, were the organic molecules that generated Earth's first life.
"None of those ideas make these experiments irrelevant," countered linkurl:David Grinspoon,;http://www.dmns.org/science/museum-scientists/david-grinspoon the curator of astrobiology at the Denver Museum of Nature and Science, who was not involved with the study. "It's still a very interesting set of experiments to inquire about the chemistry produced in the local environments of sulfur-rich volcanoes on the early Earth."
In addition to yielding clues about the origin of life on Earth, the old experiment may hold implications for the existence of life elsewhere in the universe, the authors argue. The relative abundances of the amino acids generated in the experiment were strikingly similar to those found on carbonaceous chondrite meteorites. These primitive and unaltered meteorites are thought to represent the basic material and chemistry in the universe.
"Something about the way these things were produced in the experimental apparatus mimics the way amino acids were produced in these meteorites," said Grinspoon. "It implies a universality to those chemical pathways that is very relevant to thinking about life elsewhere in the universe."
E.T. Parker et al., "Primordial synthesis of amines and amino acids in a 1958 Miller H2S-rich spark discharge experiment," Proceedings of the National Academy of Sciences, 2011, DOI: linkurl:10.1073/pnas.1019191108;http://www.pnas.org/content/early/2011/03/14/1019191108.abstract
|Miller's spark apparatus he designed with Urey in teh 1950's. |
Image: Wikimedia Commons
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