Human Origins / Arctic & Antarctic

That is a good start, but it leaves unanswered the question: How do you get from tiny snippets of RNA to longer, well-crafted chains that could have acted as the first enzymes, doing fancy things like copying themselves The shortest RNA enzyme chains known today are about 50 bases long; most have more than 100. To work effectively, moreover, an RNA enzyme must fold correctly, which requires exactly the right sequence of bases.

A young scientist named Alexander Vlassov stumbled upon a possible answer. He was working at SomaGenics, a biotech company in Santa Cruz, California, to develop RNA enzymes that latch on to the hepatitis C virus. His RNA enzymes were behaving strangely: They normally consisted of a single segment of RNA, but every time he cooled them below freezing to purify them, the chain of RNA spontaneously joined its ends into a circle, like a snake biting its tail. As Vlassov worked to fix the technical glitch, he noticed that another RNA enzyme, called hairpin, also acted strangely. At room temperature, hairpin acts like scissors, snipping other RNA molecules into pieces. But when Vlassov froze it, it ran in reverse: It glued other RNA chains together end to end.

Vlassov and his coworkers, Sergei Kazakov and Brian Johnston, realized that the ice was driving both enzymes to work in reverse. Normally when an enzyme cuts an RNA chain in two, a water molecule is consumed in the process, and when two RNA chains are joined, a water molecule is expelled. By removing most of the liquid water, the ice creates conditions that allow the RNA enzyme to work in just one direction, joining RNA chains.

The SomaGenics scientists wondered whether an icy spot on early Earth could have driven a primitive enzyme to do the same. To investigate this, they introduced random mutations into the hairpin RNA, shortened it from its normal length of 58 bases, and even cut it into pieces—all in an effort to produce RNA enzymes that were as dodgy and imperfect as early Earth’s first enzymes likely were. These pseudoprimitive RNA enzymes do nothing at room temperature. But freeze them and they become active, joining other RNA molecules at a slow but measurable rate.

These findings inspired a theory that the first, extremely inefficient RNA enzymes got help from ice, which created an environment that encouraged short segments of RNA to stick together and behave as a single, larger RNA molecule. “Freezing stabilizes the complexes formed from multiple pieces of RNA,” concludes Kazakov. “So small pieces of RNA could be enzymes, not just large 50-base molecules.”

Equally telling, the pseudoprimitive RNA enzymes that Vlassov made grabbed and joined just about any other molecule. Enzymes on early Earth might have done the same, joining random segments of 5 or 10 RNA bases to form a variety of sequences.

All these processes would occur in microscopic pockets of liquid within the ice. “You have billions and billions of different possibilities,” Trinks says, “because you have billions of these small channels,” each like a microscopic test tube containing a unique RNA experiment. On the young Earth, pockets of liquid could have expanded into a network of channels that mixed their contents during freeze-thaw cycles, like day-night temperature changes in summer. In winter, the liquid pores would have contracted and become isolated again, returning to their separate experiments. With all the mixing, something special might eventually have formed: an RNA molecule that made rough copies of itself. And as Earth warmed, these molecules might have found a home in newly thawed seas or ponds, where something even more complex might have emerged—such as a cell-like membrane. “You have something that is multiplying itself, and you have variation that is inherited,” says Antonio Lazcano, a biology researcher and professor at the National Autonomous University of Mexico, in Mexico City?. “There you have the onset of Darwinian evolution. I’m willing to call that living.”

No one can really know if this is how life began. Other theories posit that mineral surfaces organized key molecules or volcanic sources synthesized amino acids. These theories need not be mutually exclusive. Glaciers on early Earth could have scooped up mineral dust; volcanoes could have rained ash onto nearby sea ice. Primordial ice “must have been full of impurities,” Lazcano says, “and those impurities must have had catalytic effects, enhancing the synthesis or destruction of some compounds.”

Shortly after Miller finished his 25-year experiment, he suffered a stroke that ended his career. His laboratory, with 40 years of samples, was emptied in 2002 to make way for a building renovation. Experiments that had run for years or decades were discarded without ever being analyzed. As Bada rescued a few items from his mentor’s freezer, safety personnel stood by in hazmat suits, sent by university officials concerned about rumors of toxic cyanide. Any sample that couldn’t be identified was incinerated. Miller was present for a few hours of this ordeal, struggling to find words to identify the vials that he had known so well.

Miller died on May 20, 2007, but the provocative theory he helped nurture lives on. In the latest twist, Miller’s ideas are influencing not just theories about life’s origin on Earth but also investigations about the potential for life elsewhere in the solar system. In fact, it was a dinner conversation with Bada regarding Jupiter’s moon Europa that prompted Miller to open his 25-year-old samples back in 1997. While most scientists were focusing on the possibility of life in Europa’s ocean, he and Bada had been talking about what biochemistry might happen in the 10-mile-thick layer of ice atop the ocean. Those speculations are more relevant than ever, with recent discoveries of geysers on Saturn’s icy moon Enceladus and elaborate organic molecules on Titan, another Saturnian moon. Recent studies show that Mars too has vast quantities of buried ice, especially at its poles.

If life arose in one of these frozen zones, it might still exist there. Although life as we know it requires liquid water, there are places where life survives well below freezing. In the microscopic veins that permeate Arctic ice, for example, the high concentration of salt can maintain traces of water in a liquid state down to –65°F. Bacteria and diatoms inhabit those liquid veins, and Hajo Eicken, a glaciologist at the University of Alaska at Fairbanks, suspects that similar habitats could exist in the lower, warmer layers of ice on Europa, and perhaps on the other moons as well. “There’s potentially hundreds of meters of ice, if not maybe a few kilometers, that may well be quite habitable,” Eicken says.

Liquid water—and life—occurs in other cold places, too. Films of liquid water persist far below freezing, like coatings of condensation, on the surfaces of some minerals. Under some conditions, these films may stay liquid down to –90°F. Bacteria beneath films of liquid water only several molecules thick have been found clinging to microscopic grains of clay in ice cores from Greenland. Slowly consuming the iron in a single grain, these bacteria could get by for a million years before exhausting their food supply; at colder temperatures, where metabolic demands are lower, they might survive hundreds of millions of years.

If life arose in ice on Earth, then why not on Mars, Europa, or Enceladus? “You’ve got to keep an open mind in this business,” Bada says. “If I were going to make a bet about what we’d find if we discover life elsewhere in the universe, I would suspect it would be more cold-adapted than hot-adapted.”