Miller-Urey Amino Acids, circa 1953

Courtesy of Adam Johnson

When chemistry graduate student Stanley Miller first heard University of Chicago professor and Nobel laureate Harold Urey's idea that organic compounds, such as amino acids, arose in a reducing atmosphere, Miller was determined to find out. Together, they built the spark-charge apparatus—two glass flasks connected by glass tubing. Miller filled one flask with water to represent the ocean; to the other, he sucked out oxygen and pumped in methane, ammonium, and hydrogen—the chemicals then believed to comprise the early atmosphere. Miller used electrodes to generate a spark in the "atmosphere" flask, simulating early lightning. After one week, Miller detected the presence of five different amino acids, offering the first evidence that amino acids could be produced in the atmosphere of primitive Earth.

The findings "showed for the first time that Darwin's so-called 'warm little pond' was feasible on the early Earth," says Miller's former graduate student, Jeffrey Bada, now a geochemist at the University of California, San Diego.

More than 50 years later, just months after Miller's death in May 2007, Bada discovered hundreds of vials with dried amino acid residues from the classic experiments inside a dusty cardboard box at Miller's old UCSD office. The set of vials in the box pictured here, labeled with Miller's script, represent collections from the spark discharge apparatus and a reference for the publication where results later appeared. The discovery of samples allowed scientists to reanalyze Miller's findings using modern techniques.

Indiana University graduate student Adam Johnson revisited Miller's experiments using modern sample characterization techniques, such as high-performance liquid chromatography. He discovered nine additional amino acids from the original spark discharge study and 22 additional amino acids from experiments that tweaked the original procedure. "This is an example of a 50-some-year-old experiment that doesn't want to die, and the scientific evidence suggests maybe it shouldn't really," says Johnson.