On this date, the American chemist and biologist Stanley Lloyd Miller was born. In 1953, he (under his University of Chicago mentor, Nobelist Harold C. Urey) performed a famous experiment (the so-called Miller-Urey experiment) to determine the possible origin of life from inorganic chemicals on the primeval, just-formed Earth. They passed electrical discharges (simulating thunderstorms) through mixtures of reducing gases, such as hydrogen, ammonia, methane and water, believed to have formed the earliest atmosphere. Analysis days later showed the resulting chemicals included five amino acids: aspartic acid, glycine, alpha-amino-butyric acid, and two versions of alanine. Aspartic acid, glycine, and alanine are common building blocks of natural proteins. Other compounds included urea, aldehydes, and carboxylic acids. This experiment showed that the basic molecules of life could be synthesized from simple molecules, suggesting that Darwin’s “warm little pond” was a feasible scenario.
Interestingly, the 1953 Miller-Urey experiment had two sibling studies, neither of which was published. Vials containing the products from those experiments were recently recovered and reanalyzed using modern technology. The results were reported in the 17 October 2008 issue of the journal Science.
Miller relied on a blotting technique to identify the organic molecules he had created — primitive laboratory conditions by today’s standards. He would not have been able to identify anything present at very low levels.
Indiana University Biochemistry Program doctoral student Adam Johnson, Scripps Institution of Oceanography marine chemist Jeffrey Bada (the present Science paper’s principal investigator), National Autonomous University of Mexico biologist Antonio Lazcano, Carnegie Institution of Washington chemist James Cleaves, and NASA Goddard Space Flight Center astrobiologists Jason Dworkin and Daniel Glavin examined vials left over from Miller’s experiments of the early 1950s. Vials associated with the original, published experiment contained far more organic molecules than Stanley Miller realized — 14 amino acids and five amines.
However, “The apparatus Stanley Miller paid the least attention to gave the most exciting results,” said Johnson, lead author of the Science report. The difference between the published and two unpublished experiments is small — the unpublished experiments used a tapering glass “aspirator” that simply increased air flow through a hollow, air-tight glass device. Increased air flow created a more dynamic reaction vessel, or “vapor-rich volcanic” conditions, according to the present report’s authors. The 11 vials scientists recovered from Miller’s “second,” initially unpublished experiment produced 22 amino acids and the same five amines at yields comparable to the original experiment.
“We believed there was more to be learned from Miller’s original experiment,” Bada said. “We found that in comparison to his design everyone is familiar with from textbooks, the volcanic apparatus produces a wider variety of compounds.” Johnson added, “Many of these other amino acids have hydroxyl groups attached to them, meaning they’d be more reactive and more likely to create totally new molecules, given enough time.” The report’s authors bring up-to-date what is a plausible scenario for the origin of the earliest biochemical molecules on Earth:
Geoscientists today doubt that the primitive atmosphere had the highly reducing composition Miller used. However, the volcanic apparatus experiment suggests that, even if the overall atmosphere was not reducing, localized 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. In these volcanic plumes, HCN, aldehydes, and ketones may have been produced, which, after washing out of the atmosphere, could have become involved in the synthesis of organic molecules. 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.
Miller’s third, also unpublished, experiment used an apparatus that had an aspirator but used a “silent” discharge. This third device appears to have produced a lower diversity of organic molecules.
“This research is both a link to the experimental foundations of astrobiology as well as an exciting result leading toward greater understanding of how life might have arisen on Earth,” said Carl Pilcher, director of the NASA Astrobiology Institute, headquartered at NASA Ames Research Center in Mountain View, Calif.
- Johnson, A., Cleaves, H., Dworkin, J., Glavin, D., Lazcano, A., & Bada, J. (2008). The Miller Volcanic Spark Discharge Experiment Science, 322 (5900), 404-404 DOI: 10.1126/science.1161527
- Stanley L. Miller, “A production of amino acids under possible primitive Earth conditions, ” Science 117: 528 (15 May 1953) [DOI:10.1126/science.117.3046.528].
WARNING: The creationist Jonathan Wells of the Discovery Institute has made false and misleading claims about the Miller-Urey experiment and other abiogenesis research in his book Icons of Evolution: Science or Myth? Why Much of What We Teach About Evolution Is Wrong.