Volcanic Spark Soup Richer Than First Described
(December 4th 2008) 50 years ago, Miller and Urey demonstrated that 'sparking' mixtures of simple inorganic chemicals was sufficient to generate some of the basic building blocks of life. A new analysis of their material shows that they considerably underestimated the range of biomolecules successfully synthesised in their original experiments, reports Jeremy Garwood.
In 1951, Harold Urey, Nobel Prize winning discoverer of deuterium, proposed the characteristics for a primordial broth under a reducing atmosphere composed of methane, ammonia and hydrogen gas rather than our current atmosphere of nitrogen, oxygen and carbon dioxide. He suggested that under such conditions it would be experimentally possible to produce organic molecules from water and methane using ultraviolet radiation or lightning.
Stanley L. Miller, a young graduate student in his laboratory at the University of Chicago wanted to test Urey's theories: "Urey gave a lecture in October of 1951 when I first arrived at Chicago and suggested that someone do these experiments. So I went to him and said, 'I'd like to do those experiments'. The first thing he tried to do was talk me out of it. Then he realized I was determined. He said the problem was that it was really a very risky experiment and probably wouldn't work, and he was responsible that I get a degree in three years or so. So we agreed to give it six months or a year. If it worked out fine, if not, on to something else. As it turned out I got some results in a matter of weeks."
Sparking circulating water vapour in an atmosphere of ammonia, methane and hydrogen, Miller succeeded in synthesising five amino acids. His classic experiment, "A Production of Amino Acids under possible primitive earth conditions", was published in Science magazine in 1953.
Following Miller's death in May 2007, one of his former graduate students, Jeffrey L. Bada, found boxes containing hundreds of vials of dried residues collected from the experiments conducted in 1953 and 1954. Identifying the vials from Miller's original notebooks, Bada, now at Scripps Institute for Oceanography in San Diego, discovered that Miller had in fact conducted three series of experiments, two of which were never published.
Miller's original apparatus consisted of a glass flask at the bottom, containing an "ocean" of water, which he heated, forcing water vapour to circulate through the apparatus. The flask at the top contained an "atmosphere" consisting of methane, ammonia, and hydrogen gases and the circulating water vapour. He exposed this gaseous mixture to a continuous electrical discharge ("lightning"), causing them to interact. Water-soluble products from these reactions then passed through a condenser and dissolved in the mock ocean. Miller left his apparatus running for a week - after a day, the water in the flask "became noticeably pink", after a week, it was "deep red and turbid".
Bada learnt that Miller had also constructed two variations of this original apparatus. One simply used a different spark generator. The second used a tapering glass "aspirator" to increase air flow, injecting steam onto the sparks. This caught Bada's attention, because he says it simulates "vapor-rich volcanic conditions", replicating what might have existed in lagoons and tidal pools around volcanoes on the primordial earth.
Adam P. Johnson, a graduate student at Indiana University, was visiting Bada's laboratory on an internship. He jumped at the opportunity to work on the analysis of the "brown residue at the bottom of (the) old vials". As recently reported in Science magazine, he found more amino acids in vials from the original experiment, but the best results came from the "volcanic experiment", in which he identified 22 amino acids and five amines, more than in Miller's original experiment, and at comparable yields, in the milligram range.
As Miller once said of his original work: "The fact that the experiment is so simple that a high school student can almost reproduce it is not a negative at all. That fact that it works and is so simple is what is so great about it. If you have to use very special conditions with a very complicated apparatus there is a question of whether it can be a geological process."
However, since 1953, there have been other ideas about the conditions existing on the primitive earth. In particular, there are doubts that the atmosphere would have had such a highly reducing composition. Nevertheless, Bada argues that even if the overall atmosphere was not reducing, such microenvironments could have existed around volcanoes.
"Miller's volcanic apparatus experiment suggests that localised prebiotic synthesis could have been effective. Reduced gases and lightning associated with volcanic eruptions in hot spots or island arc-type systems could have been prevalent on the early earth before extensive continents formed."
Also, in contrast to those arguing for an oceanic origin, Bada suggests that volcanic pools and tidal areas would have permitted a better concentration of material. "Amino acids formed in volcanic island systems could have accumulated in tidal areas, where they could be polymerized by carbonyl sulfide, a simple volcanic gas that has been shown to form peptides under mild conditions."
