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One morning in late 1997, Stanley Miller lifted a glass vial from a cold, bubbling vat. For 25 years he had tended the vial as though it were an exotic orchid, checking it daily, adding a few pellets of dry ice as needed to keep it at –108 degrees Fahrenheit. He had told hardly a soul about it. Now he set the frozen time capsule out to thaw, ending the experiment that had lasted more than one-third of his 68 years.
Miller had filled the vial in 1972 with a mixture of ammonia and cyanide, chemicals that scientists believe existed on early Earth and may have contributed to the rise of life. He had then cooled the mix to the temperature of Jupiter’s icy moon Europa—too cold, most scientists had assumed, for much of anything to happen. Miller disagreed. Examining the vial in his laboratory at the University of California at San Diego, he was about to see who was right.
As Miller and his former student Jeffrey Bada brushed the frost from the vial that morning, they could see that something had happened. The mixture of ammonia and cyanide, normally colorless, had deepened to amber, highlighting a web of cracks in the ice. Miller nodded calmly, but Bada exclaimed in shock. It was a color that both men knew well—the color of complex polymers made up of organic molecules. Tests later confirmed Miller's and Bada’s hunch. Over a quarter-century, the frozen ammonia-cyanide blend had coalesced into the molecules of life: nucleobases, the building blocks of RNA and DNA, and amino acids, the building blocks of proteins. The vial’s contents would support a new account of how life began on Earth and would arouse both surprise and skepticism around the world.
Miller had filled the vial in 1972 with a mixture of ammonia and cyanide, chemicals that scientists believe existed on early Earth and may have contributed to the rise of life. He had then cooled the mix to the temperature of Jupiter’s icy moon Europa—too cold, most scientists had assumed, for much of anything to happen. Miller disagreed. Examining the vial in his laboratory at the University of California at San Diego, he was about to see who was right.
As Miller and his former student Jeffrey Bada brushed the frost from the vial that morning, they could see that something had happened. The mixture of ammonia and cyanide, normally colorless, had deepened to amber, highlighting a web of cracks in the ice. Miller nodded calmly, but Bada exclaimed in shock. It was a color that both men knew well—the color of complex polymers made up of organic molecules. Tests later confirmed Miller's and Bada’s hunch. Over a quarter-century, the frozen ammonia-cyanide blend had coalesced into the molecules of life: nucleobases, the building blocks of RNA and DNA, and amino acids, the building blocks of proteins. The vial’s contents would support a new account of how life began on Earth and would arouse both surprise and skepticism around the world.
Although one of Miller’s final experiments, it certainly wasn’t the final word. The last several years have seen a steady stream of corroborating evidence, including one experiment—so new it has not yet been published—that Miller’s colleague, the late Leslie Orgel, called “astonishing.”
For decades, those studying the origin of life have imagined that it emerged in balmy conditions from primordial soups, tropical ponds, even boiling volcanic vents. Miller and a few other scientists began to suspect that life began not in warmth but in ice—at temperatures that few living things can now survive. The very laws of chemistry may have favored ice, says Bada, now at the Scripps Institution of Oceanography in La Jolla, California. “We’ve been arguing for a long time,” he says, “that cold conditions make much more sense, chemically, than warm conditions.”
For decades, those studying the origin of life have imagined that it emerged in balmy conditions from primordial soups, tropical ponds, even boiling volcanic vents. Miller and a few other scientists began to suspect that life began not in warmth but in ice—at temperatures that few living things can now survive. The very laws of chemistry may have favored ice, says Bada, now at the Scripps Institution of Oceanography in La Jolla, California. “We’ve been arguing for a long time,” he says, “that cold conditions make much more sense, chemically, than warm conditions.”
Miller’s frozen experiment is a striking testament to the idea. Although life requires liquid water, small amounts of liquid can persist even at –60°F. Microscopic pockets of water within the ice may have gathered simple molecules like the ones Miller synthesized, assembling them into longer and longer chains. A single cubic yard of sea ice contains a million or more liquid compartments, microscopic test tubes that could have created unique mixtures of RNA that eventually formed the first life.
If life on Earth arose from ice, then our chances of finding life elsewhere in the solar system—not to mention elsewhere in the galaxy—may be better than we ever imagined.
The vial of ammonia and cyanide chilling in Miller’s lab was just one of the chemical cocktails he kept, aging like wine in a cellar. Some of the samples sat in freezers, others under the sink, and still others in water baths maintained at various temperatures. They were part of an effort to understand chemical reactions that must have unfolded over millennia on early Earth. The location of every sample was stored in Miller’s head; occasionally he would give one to a student to analyze.
If life on Earth arose from ice, then our chances of finding life elsewhere in the solar system—not to mention elsewhere in the galaxy—may be better than we ever imagined.
The vial of ammonia and cyanide chilling in Miller’s lab was just one of the chemical cocktails he kept, aging like wine in a cellar. Some of the samples sat in freezers, others under the sink, and still others in water baths maintained at various temperatures. They were part of an effort to understand chemical reactions that must have unfolded over millennia on early Earth. The location of every sample was stored in Miller’s head; occasionally he would give one to a student to analyze.
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.
“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.
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.
In July 2002 a small skiff dropped Hauke Trinks on the beach of Nordaustland, a rocky island encased in glaciers and nearly devoid of plants. Trinks, then a physicist at the Technical University of Hamburg-Harburg in Germany, had come to Nordaustland—far north of the Arctic Circle—to peer 4 billion years back in time to an era shortly after the end of the bombardment of Earth by asteroids. According to some solar evolution models, the sun was some 30 percent dimmer at that time, providing less heat to Earth. So as soon as the hail of asteroids stopped, Earth may have cooled to an average surface temperature of –40°F and a crust of ice as much as 1,000 feet thick may have covered the oceans. Many scientists have puzzled over how life could have arisen on a planet that was essentially a giant snowball. The answer, Trinks suspected, involved sea ice.
Trinks had become interested in sea ice 10 years before, while studying its tendency to accumulate pollutants from the atmosphere and concentrate them in liquid pockets within the ice. He set out to explore whether a layer of ice covering early Earth’s oceans might have gathered and assembled organic molecules.
Trinks had become interested in sea ice 10 years before, while studying its tendency to accumulate pollutants from the atmosphere and concentrate them in liquid pockets within the ice. He set out to explore whether a layer of ice covering early Earth’s oceans might have gathered and assembled organic molecules.
With a few crates of supplies and two sled dogs, Trinks and his partner, Marie Tieche, hunkered down in a cabin on Nordaustland for 13 months. Each morning they monitored the temperature of the ice and prepared the day’s experiments. To study the networks of liquid pockets, Trinks injected dyes into the ice and watched through a microscope as they spread.
Winter deepened, 24-hour darkness descended, and the mercury plummeted to –20°F. Trinks continued his experiments, sometimes banging pans together to chase polar bears away. Once a walrus lunged up through the ice and dragged several of Trinks’s instruments into the ocean.
He built a makeshift lab table from planks of wood and discarded gasoline cans. He examined slices of sea ice under the microscope, his hood pulled tight around his eyes. Turning a knob with a gloved hand, he nudged a metal electrode nearly as fine as a red blood cell closer to an ice crystal. The needle on his voltmeter jerked sideways, registering a sharp drop in voltage on the crystal’s surface—evidence of a microscopic electric field that might arrange and orient molecules on the ice’s surface.
Winter deepened, 24-hour darkness descended, and the mercury plummeted to –20°F. Trinks continued his experiments, sometimes banging pans together to chase polar bears away. Once a walrus lunged up through the ice and dragged several of Trinks’s instruments into the ocean.
He built a makeshift lab table from planks of wood and discarded gasoline cans. He examined slices of sea ice under the microscope, his hood pulled tight around his eyes. Turning a knob with a gloved hand, he nudged a metal electrode nearly as fine as a red blood cell closer to an ice crystal. The needle on his voltmeter jerked sideways, registering a sharp drop in voltage on the crystal’s surface—evidence of a microscopic electric field that might arrange and orient molecules on the ice’s surface.
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