After decades of languishing in a cardboard box, unanalyzed vials from a famous chemistry experiment have been brought back to the lab, revealing new clues to the beginnings of life on Earth.
Over 50 years ago, Stanley Miller, then a 23-year-old graduate student, conducted an experiment that is now a staple of biology. Miller and his adviser, Nobel laureate Harold Urey, showed that amino acids, the building blocks of proteins, could be made from a cocktail of basic precursors, the so-called primordial soup.
A research team led by Miller’s former graduate student Jeffrey Bada analyzed leftovers from a variation on this experiment. The researchers report in the Oct. 17 Science that remnants from an experiment conducted with a simulated volcanic environment contain an even larger number of biologically important amino acids.
Urey and Miller re-created what they thought was the atmosphere of early Earth — a stew of methane, ammonia, hydrogen and water — and zapped the contents with an electric shock similar to lightning. After a night of sparking, the vial turned red, then yellow and finally brown, indicating the presence of compounds. Analyses confirmed the presence of a mixture of amino acids, which, at the time, many scientists thought were the basis of life.
“From the historical point of view, the Miller experiment transformed the study of the origin of life in the ’50s into an important research field,” says Pascale Ehrenfreund, an astrobiologist at GeorgeWashingtonUniversity in Washington, D.C.
Miller published his results in a brief, influential report in Science in 1953. Bada, a geochemist at Scripps Institution of Oceanography in La Jolla, Calif., reports his team’s reanalysis of that experiment also in Science, 55 years later.
“This all began when Antonio Lazcano casually mentioned that Stanley had some unanalyzed vials left over from the ’50s,” Bada says. Lazcano, of the Universidad Nacional Autónoma de México, is a coauthor on the latest Science report.
Before Miller died last year, the contents of his lab, including laboratory experiments and notebooks, were moved to Bada’s laboratory at Scripps. When Bada heard of the existence of the vials, he went back to his lab and began digging.
“We found these dusty Scotch-taped boxes, all carefully labeled. We were able to match the samples to Stanley’s lab notebook. It was so typical of Stanley, so nonchalant,” says Bada. Miller had described the volcanic experiment in notebooks, but never published the results.
Bada and lead author Adam Johnson, a biochemist at IndianaUniversity, Bloomington, noticed that some of the vials’ contents were created in the presence of a stream of water vapor, which simulated the local environment of a volcano. The team carefully reconstituted the dried material in these vials, and analyzed the contents with modern techniques.
The team not only identified amino acids similar to the ones Miller reported in 1953 from the experiment without the steam jet, but also identified 10 types of amino acids not found in the original setup. Bada’s team concludes that the infusion of a jet of steam creates a more diverse mixture of amino acids.
“Being able to analyze 50-year-old residues with new laboratory techniques and equipment is an exciting adventure,” says Ehrenfreund.
While Miller’s original results have been replicated many times over, some geobiologists today question the relevance of his findings. They argue that early Earth’s environment was probably not like the unstable, reactive one Miller and Urey proposed. No one knows for sure, but most scientists today think it was milder than Miller and Urey’s assumption. The new report in Science argues that global conditions may not have mattered, because volcanoes belch reactive gas and steam into the atmosphere, creating local conditions that could be conducive to life.
“The model is that you have these small pockets, volcanic hot spots,” explains Bada, in which a volatile reducing atmosphere, one in which chemicals are more likely to react with one another, may have produced amino acids.
The team’s reanalysis makes it plausible that a shallow tide pool tucked into the side of a volcano and a fortuitous bolt of lightning could have led to an abundance of amino acids.
“The local volcanic scenario is clearly more favorable for synthesis than the classical version of this experiment,” explains Alan Schwartz, a scientist who studies the origins of life at Radboud University Nijmegen in the Netherlands.
Of course, the world has changed substantially since 1953. Questions about the origin of nucleic acids like DNA and RNA may take center stage today, but Miller’s original experiment, and what it told the world about life’s beginnings, has its place in history.
“I am sure that Stanley Miller would have been pleased by this report,” says Schwartz.
Gustaf Arrhenius, a former colleague of Miller’s at Scripps who also explores the beginnings of life, agrees. “Anybody would wish for himself to have a group of competent followers dedicated to examining the abandoned belongings of the past master and be lucky enough to be able to add to his legacy.”