A fresh look at forgotten vials from Stanley Miller's primordial-soup-in-a-bottle experiments implies that volcanoes seeping hydrogen sulfide helped form some of life's earliest ingredients.

Sulfur's presence makes it possible to synthesize a greater variety of amino acids – the molecules that link to form protein chains – and gives nascent life a larger palette of chemicals from which to select.

"When you are analyzing old samples, you always hope in the back of your mind that you are going to find something really cool," says primary author Eric Parker, a graduate student now at Georgia Tech. "It was a pleasant surprise to see such a large array of different amino acids and amines."

In Miller's classic experiments, dating from the early 1950s, electricity – standing in for lightning – zaps a few basic chemicals, water, methane, hydrogen and ammonia, to simulate the atmospheric conditions on Earth before life began. Miller became famous for showing that simple chemicals could be combined with relative ease to form some of the building blocks of life.

This 1958 experiment, originally unpublished and revisited March 21 in the Proceedings of the National Academy of Sciences, marked Miller’s first inclusion of hydrogen sulfide, the chemical that makes rotten eggs smell and a prime component of volcanic gas emissions, in the primordial mix.

Using modern chemical analysis techniques, Parker's team found 23 amino acids, seven other compounds and four amines, a breakdown product of amino acids. This was far more than typical analysis of past samples, which yielded five to 10 amino acids. Several of the amino acids were synthesized for the first time, including methionine, a required building block for many proteins in animals, plants and fungi.

The newly identified collection of amino acids is also similar to those found in meteorites, meaning sulfur may have help assemble life's ingredients off this planet, as well as on.

Sandra Pizzarello, an Arizona State University chemist who was not involved with the study, agreed with Parker's chemical detective work. She noted, however, that all experiments seeking to synthesize prebiotic chemicals are limited.

Earth's early atmospheric conditions aren't known, and the reactions in this experiment could only have happened near a source of sulfur. On a primordial Earth, that would have meant volcanoes. Whereas Miller originally focused on chemical reactions in the atmosphere, the primordial soup may have gathered in a volcanic bowl.

Volcanic origins were suggested by a 2008 reanalysis of another forgotten Miller experiment conducted by Jim Cleaves, a geochemist at the Carnegie Institution of Washington, and Scripps Institute of Oceanography biochemist Jeffrey Bada. Both are former students of Miller, and plan to revisit more of his old experiments.

"Miller was a real packrat. He didn't throw anything out," said Cleaves, Miller’s final lab student and inheritor of the lab. "Sitting on the shelf was this box, I thought, 'I don't know what these are, but I can't bear to throw them out!'"

Images: 1) Stanley Miller in his UC San Diego lab in 1970/UCSD* Archives.*

See Also:

*Citation: “Primordial Synthesis of Amines and Amino Acids in a 1958 Miller H2S-rich Spark Discharge Experiment.” By Eric T. Parker, H. James Cleaves, Jason P. Dworkin, Daniel P. Glavin, Michael P. Callahan, Andrew D. Aubrey, Antonio Lazcano, and Jeffrey L. Bada. Proceedings of the National Academy of Sciences U.S.A., Mar. 21, 2011. *