Originally considered a dud, an old volcano-in-a-bottle experiment designed to mimic conditions that may have brewed the components of life might have been right on target.
After reanalyzing the results of unpublished research conducted by Stanley Miller in 1953, chemists realized that his experiment had actually produced a wealth of amino acids — the protein foundation of life.
Miller is famed for the results of experiments on amino acid formation in a jar filled with methane, hydrogen and ammonia — his version of the primordial soup. However, his estimates of atmospheric composition were eventually considered inaccurate. The experiment became regarded as a general rather than useful example of how the first organic molecules may have assembled.
But the latest results, derived from samples found in an old box by one of Miller's former graduate students, come from a device that mimicked volcanic conditions now believed to have existed three billion years ago. The findings suggest that amino acids could have formed when lightning struck pools of gas on the flanks of volcanoes, and are a fitting coda for the late father of prebiotic chemistry.
"What's amazing is that he did it," said study co-author Jeffrey Bada, a Scripps Institute of Oceanography biochemist and Miller's former student. "All I did is have access to his extracts."
Bada stumbled across the original experiment by accident when a colleague of Miller's mentioned having seen a box of experimental samples in Miller's office. Bada, who inherited Miller's scientific possessions after his death in 2007, found the box — literally labeled "1953-1954 experiments" — in his own office.
Inside it were samples taken by Miller from a device that spewed a concentrated stream of primordial gases over an electrical spark. It was a high-powered variation on the steady-steam apparatus that earned him fame — but unlike that device, it appeared to have produced few amino acids, and was unmentioned in his landmark 1953 Science study, "A Production of Amino Acids Under Possible Primitive Earth Conditions."
But Miller didn't have access to high-performance liquid chromatography, which lets chemists break down and classify samples with once-unthinkable levels of precision. And when Bada's team reanalyzed the disregarded samples, they found no fewer than 22 amino acids, several of which were never seen by Miller in a lifetime of primordial modeling.
Perhaps amino acids first formed when the gases in Miller's device accumulated around active volcanoes, said Bada. "Instead of having global synthesis of organic molecules, you had a lot of little localized factories in the form of these volcanic islands," he said.
"The amino acid precursors formed in a plume and concentrated along tidal shores. They settled in the water, underwent further reactions there, and as they washed along the shore, became concentrated and underwent further polymerization events," explained Indiana University biochemist Adam Johnson, a co-author of the study. "And lightning" — the final catalyst in the equation — "tends to be extremely common with volcanic eruptions."
Luke Leman, a Scripps Institute biochemist who was not involved in the study, published today in Science, agreed.
"These findings add to a growing body of literature suggesting that areas near volcanoes could have been hotspots of organic chemistry on early Earth," he said.
Leman continued, "These findings will likely inspire a next generation of prebiotic chemists, much as Miller's original experimental results have inspired the field for more than fifty years."
Added Bada, "There's a lesson here: don't throw anything away."
The Miller Volcanic Spark Discharge Experiment