Matthew Levy, once a graduate student of Miller’s and now a molecular biologist at the Albert Einstein College of Medicine in New York City, recalls being handed one of the 25-year-old samples to work on. “I was scared,” he says. “I was thinking, these samples are older than I am.” Levy burned holes in his shirts over the next few weeks as he dissolved the samples with hydrochloric acid and ran them through an instrument called a high-performance liquid chromatograph to identify the chemicals that had formed. Red and green pens on the device traced out telltale peaks on a scrolling strip of paper. Those peaks corresponded to seven different amino acids and 11 types of nucleobases.
“What was remarkable,” Bada says, “is that the yield in these frozen experiments was better, for some compounds, than it was with room-temperature experiments.”
There were people who found the results a little too remarkable. When Bada and Miller submitted their findings to a top-tier science journal, the article was rejected. A reviewer of the manuscript felt that those molecules must surely have formed while the samples were thawing, not while frozen at the ridiculously low temperature of –108°F. So Miller, Bada, and Levy did more experiments to show that thawing played no role. They published their results in another journal, Icarus, in 2000.
The skepticism they faced was understandable. Chemical reactions do slow down as the temperature drops, and according to standard calculations, the reactions that assemble cyanide molecules into amino acids and nucleobases should run a hundred thousand times more slowly at –112°F than at room temperature. By that reckoning, even if Miller had run his experiment for 250 years—let alone 25—he should have seen nothing.
This is the main argument against Miller’s experiment, and against a cold origin of life in general. But strange things happen when you freeze chemicals in ice. Some reactions slow down, but others actually speed up—especially reactions that involve joining small molecules into larger ones. This seeming paradox is caused by a process called eutectic freezing. As an ice crystal forms, it stays pure: Only molecules of water join the growing crystal, while impurities like salt or cyanide are excluded. These impurities become crowded in microscopic pockets of liquid within the ice, and this crowding causes the molecules to collide more often. Chemically speaking, it transforms a tepid seventh-grade school dance into a raging molecular mosh pit.
“Usually as you cool things, the reaction rates go down,” concluded Leslie Orgel, who studied the origins of life at the Salk Institute in La Jolla, California, from the 1960s until his death last October. “But with eutectic freezing, the concentrations go up so fast that they more than make up” for the difference.
Cyanide is a good candidate as a precursor molecule in the life-in-a-freezer model for several reasons. First, planetary scientists suspect that cyanide was abundant on early Earth, deposited here by comets or created in the atmosphere by ultraviolet light or by lightning (once the atmosphere became oxygen rich, 2.5 billion years ago, the process would have stopped). Second, although cyanide is lethal to modern animals, it has a convenient tendency to self-assemble into larger molecules. Third, and perhaps most important, no matter how much cyanide rained down, it could become concentrated only in a cold environment—not in warm coastal lagoons—because it evaporates more quickly than water.
“The strong point of freezing,” according to Orgel, “is that you concentrate things very efficiently without evaporation.” Freezing also helps preserve fragile molecules like nucleobases, extending their lifetime from days to centuries and giving them time to accumulate and perhaps organize into something more interesting—like life.
Orgel and his coworkers proposed these ideas in 1966, when he showed that frozen cyanide efficiently assembles into larger molecules. Alan Schwartz, a biochemist at the University of Nijmegen in the Netherlands, took the idea further when he showed in 1982 that frozen cyanide, in the presence of ammonia, can form a nucleobase called adenine. And Stanley Miller likely had the eutectic effect in mind when he stowed his now famous samples in a freezing chamber full of dry ice and acetone.
While Miller and Orgel followed their clues in the lab, other scientists pursued their obsession with life’s chilly origins to the ends of the earth.