Human Origins / Arctic & Antarctic

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02.01.2008

Did Life Evolve in Ice?

Funky properties of frozen water may have made life possible.

by Douglas Fox

scientist Hauke TrinksHauke Trinks spent 13 months in the Far North studying ice and its potential as an incubator for life.

Image courtesy of Marie Tieche

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.




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.”

polar bearImage courtesy of Marie Tieche

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.

 

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