What kind of chemistry occurs in conditions that approximate those of the primitive earth, and what can that tell us about the origin of life? Scientists have been avidly pursuing the origins of life since the early 1900's. While still a graduate student in Nobel laureate Harold Urey's lab, Stanley Miller truly began the modern era of prebiotic chemistry with a publication in the May 15th, 1953 issue of Science. His work rocked the science world and actually overshadowed Watson and Crick's work on the DNA double helix, which was published one month earlier in Nature. Now, scientists have rediscovered some of Miller's early samples and find that, even after his death, Miller still has more to tell us.

Miller's classic experiment involved putting atmospheric components thought to reflect those of the early Earth (ammonia, hydrogen, methane, and water) in a closed system and stimulating that mixture with an electric current to mimic the effects of lightning storms. He generated a small number of biochemically significant compounds, including amino acids, hydroxy acids, and urea, showing that conditions of primitive earth can create the building blocks of life.

When Miller died on May 20th, 2007, the science community lost a true pioneer. However, his former graduate students and colleagues never forgot him, and have continued his work. More than half a century after the initial experiments, a team of scientists (which includes some of Miller's first and last graduate students) discovered vials of samples that Miller saved from 1953. The samples were from three different experimental designs, and two of them were not included in the 1953 Science paper. His protégés reexamined the contents of those vials using modern techniques (high-performance liquid chromatography and time-of-flight mass spectrometry) and published the results today, once again in Science.

Specifically, they reanalyzed 11 vials from an apparatus that was slightly modified from the original; it had an additional aspirating nozzle that was attached to a flask containing water. This nozzle injected jets of steam and gas into the spark created by the electrodes, which would simulate lightning striking at the site of a steam-rich volcanic area. They found that the residues from this apparatus contained 22 amino acids and 5 amines, which is a slightly more complex mix than the results of the experiment that was published in 1953.

These results could address some of the criticism of Miller's earliest work. Many geoscientists have questioned the accuracy of the simulated primitive atmosphere—they proposed that Miller wrongly assumed that early earth had a highly reducing atmosphere, one with little to no free oxidizing compounds. Miller's colleagues now argue that the amino acids produced by the volcanic apparatus indicate 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 in the early Earth."

The debate regarding the origins of life will continue on for some time. We have yet to reach Miller's dream of discovering and experimentally demonstrating a reasonable explanation for how prebiotic chemicals assembled into macromolecules (DNA, RNA, and proteins) and then into living cells. But however it works out, future discoveries will owe a lot to Miller's contributions, as he essentially started the experimental field of prebiotic chemistry.

Science, 2008. DOI: 10.1126/science.1161527