A new look at Stanley Miller’s experiments at the University of Chicago in the early 1950s offers up an intriguing speculation: Volcanic eruptions on the early Earth may have been crucial for the development of life. Miller used hydrogen, methane and ammonia to re-create what was then believed to be the the primordial atmosphere on our planet, operating with closed flasks containing water in addition to the gases. An electric spark was then used to simulate lightning, and as anyone who has ever cracked a textbook knows, the water became laden with amino acids after a few weeks.
Image A: The apparatus used for Miller’s original experiment. Boiled water (1) creates airflow, driving steam and gases through a spark (2). A cooling condenser (3) turns some steam back into liquid water, which drips down into the trap (4), where chemical products also settle. Credit: Ned Shaw, Indiana University.
It never occurred to me that samples from the original experiments might have survived after all these years, but fortunately Jeffrey Bada (University of California at San Diego) discovered them after Miller’s death in 2007. And given the increasing sophistication of our tools for chemical analysis, it was a natural move to look for chemicals within those samples that might have eluded detection fifty years ago. Working with and re-interpreting old data is fascinating enough and is going to become more and more common in all the sciences, now that computers have given us the ability to generate and store such vast quantities of information. But re-analyzing samples from experiments as historic as these to pull out new insights puts a bit of a chill down the spine. If only Miller could have known about this work!
Miller’s three different experiments included one that injected steam into the gas to simulate a volcanic cloud, and it turns out that it is that experiment that produced the widest variety of compounds. The work, performed at NASA GSFC, turned up fruitful results indeed, some 22 amino acids, ten of which were new to this kind of experiment. A key factor is the change in our thinking about the ancient atmosphere, which is now believed to have been composed mostly of carbon dioxide, carbon monoxide and nitrogen rather than the mix Miller originally used.
Image B: The apparatus used for Miller’s “second,” initially unpublished experiment. Boiled water (1) creates airflow, driving steam and gases through a spark (2). A tapering of the glass apparatus (inlay) creates a spigot effect, increasing air flow. A cooling condenser (3) turns some steam back into liquid water, which drips down into the trap (4), where chemical products also settle. Credit: Ned Shaw, Indiana University.
How do changing views of the atmosphere affect the outcome? Daniel Glavin (GSFC), who analyzed the samples at Goddard, has this to say:
“At first glance, if Earth’s early atmosphere had little of the molecules used in Miller’s classic experiment, it becomes difficult to see how life could begin using a similar process. However, in addition to water and carbon dioxide, volcanic eruptions also release hydrogen and methane gases. Volcanic clouds are also filled with lightning, since collisions between volcanic ash and ice particles generate electric charge. Since the young Earth was still hot from its formation, volcanoes were probably quite common then. The organic precursors for life could have been produced locally in tidal pools around volcanic islands, even if hydrogen, methane, and ammonia were scarce in the global atmosphere. As the tidal pools evaporated, they would concentrate the amino acids and other molecules, making it more likely that right sequence of chemical reactions to start life could occur. In fact, volcanic eruptions could assist the origin of life in another way as well – they produce carbonyl sulfide gas, which helps link amino acids into chains called peptides.”
Jeffrey Bada, a co-author of the paper on this work, was Miller’s graduate student between 1965 and 1968, and continued working with the scientist in the intervening years. In addition to its provocative insight into the potential role of volcanic activity, the new work is a reminder that the things we do sometimes survive us in the most unexpected ways. I’m thinking of a particular researcher I once worked with, now gone, who would have found great pleasure in that notion. The paper is Johnson et al., “The Miller Volcanic Spark Discharge Experiment,” Science 322, No. 5900 (17 October 2008), p. 404 (abstract).