A new study in Science magazine revisits the classic Miller-Urey experiment, this time with modern analytical technology. Adam P. Johnson, a graduate student at the Indiana University, and coworkers took preserved, stored samples from the original series of origin-of-life experiments carried out by Harold Urey and his then graduate student Stanley Miller, and subjected them to a range of modern chemical techniques that are far more sensitive and comprehensive than those available in the 1950s, such as high-performance liquid chromatography and liquid chromatography–time of flight mass spectrometry.
Johnson and colleagues found 22 different amino acids, along with several other amine compounds – many more than were originally found using 1953 machinery. Significantly, dried samples from a variant of the original experimental setup, one which used electric sparks and injected sprays of steam into the distillery, yielded a much greater diversity of organics than the more famous version of the classic experiment.
Samples from the original Miller-Urey experiments had been kept safe for posterity as dried masses of orange-brown goo in little bottles. The original experiments were designed to study whether conditions on the primeval Earth could have favored the production of organic compounds which were necessary to assemble the first naturally-occurring, self-replicating molecular nanomachines (life).
Everyone knows the story by now: Urey and Miller ran their experiment, subjecting water and an atmosphere of ammonia, methane and hydrogen to electric sparks, ultraviolet light, and heat, all in a little self-contained distillery. After running their experiment for a few days, water in the still turned brown and thick. The slop was analyzed and found to contain a high concentration of amino acids, polycyclic aromatic hydrocarbons, and other organic molecules.
Over the years the Miller-Urey results have fallen in and out of favor among people studying the emergence of life on Earth. One problem with the original studies was their choice of atmosphere. Early spectroscopic readings of the atmosphere of Jupiter showed lots of ammonia and methane, which we now know aren’t there in such high concentrations. Using a more realistic early-Earth gas mix, the Miller-Urey setup doesn’t produce as much organic residue, but it does produce some.
The primordial Earth, around 4 billion years ago, was a violent world of ubiquitous volcanic activity. Hawaii-style volcanic cones would have been common, punching up through a shallow world ocean riddled with volcanic rifts and seafloor hot springs. It was a laboratory for life. Ash and dust thrown into the atmosphere by volcanoes would have meant almost continuous lightning activity, and lightning works chemistry, especially for nitrogen. These new Miller-Urey data support a model of organic compounds not only coming to Earth on comets (along with their complements of ammonia and methane) and meteors, but also raining down from a shrouded, galvanic sky. Once in the oceans, amino acids would have been drawn into submarine hot spring systems that crisscrossed the ocean floor, and that road led to life.