10.3 THIS IS HOW WE DO IT: Could life have originated in ice, rather than in a “warm little pond”?

Phenomena in the natural world don’t always give up their secrets easily. When trying to better understand some process in nature, applying a new experimental technique occasionally allows a breakthrough. Other times, it may be the discovery of new or unexpected evidence that provides the breakthrough. But sometimes progress requires a more radical approach and thinking outside the box.

Researchers have been questioning some of the most basic assumptions about life’s origin on earth, as described in the first two sections of this chapter. For example, the most widely held view is that life on earth emerged from a particular type of environment, one that was warm or hot and was wet—something along the lines of the “warm little pond” Darwin had speculated about in The Origin of Species. Evidence from the experiments of Miller and Urey, as well as other research, supports this view.

But what if icy baths, not warm ponds, were the “incubator” of life?

That’s thinking outside the box. And the researchers suggesting this idea have provided some intriguing evidence and proposed some clever ideas to support it. Their ideas build upon the broad consensus about the most important physical and chemical requirements for the initial generation of self-replicating molecules.

Chemical requirement 1 Precursor molecules need to last a while and need to come in contact with each other.

Conventional assumption: In living cells today, compartments make this duration and closeness of contact possible. But before life appeared on earth, under warm, wet conditions, some sort of chambers or microspheres may have spontaneously formed and served this purpose.

Novel approach: It turns out that, as water freezes, tiny compartments form within the ice. On early earth, low temperature may have slowed the degradation of any precursor molecules—including RNA—that formed. And the tiny compartments may have held those precursor molecules close together, making it possible for them to react with each other.

Chemical requirement 2 Precursor molecules need to exhibit catalytic properties.

Conventional assumption: At warm or hot temperatures—but not at colder temperatures—molecules move quickly and collide frequently, enhancing reaction rates.

Novel approach: Although reactions usually slow down as the temperature drops, some actually speed up. As water freezes, the ice crystals form only from pure water. If there are any impurities present—such as salt or cyanide—they are excluded from the crystals and concentrated in small chambers of liquid water within the ice. At these higher concentrations, the molecules collide more frequently, even as the temperature drops. As a consequence, certain reactions can occur more rapidly—possibly including the creation and elongation of the first RNA chains.

Intriguing observations and evidence Researchers have carried out experiments in which they prepare—and then freeze—tubes containing seawater and the building blocks of RNA. After thawing out the tubes, they find numerous RNA molecules, some long enough to be able to act as enzymes.

And recent evaluations of glacier-encased land north of the Arctic Circle suggest that 4 billion years ago, the sun may have been dimmer, and the earth may have cooled so much that ice covered the oceans. Some scientists have even gone so far as to describe earth as a “giant snowball” at that time.

There is still plenty of skepticism about the idea that the primordial soup was a cold soup. Many researchers suspect that reported evidence of RNA chains forming under freezing temperatures may reflect accidental contamination, or that the chains actually formed during the thawing-out process.

As a case study of scientific thinking in action, though, this example illuminates the importance of evaluating the assumptions underlying our hypotheses. And we get a glimpse of how a fresh perspective can remove constraints that might limit our ability to see solutions to problems.

Keeping an open mind is more important than rigidly holding onto an idea. Observations and evidence must take the central role in guiding our interpretations and understanding of natural processes.