Most discussions of the possibility of life on other worlds eventually bring in the qualifying phrase, “Life as we know it.” The definition of “life” that is most commonly cited usually involves such requirements as the ability to obtain energy from an outside source for the purpose of sustaining the metabolic reactions, the ability to reproduce in order to provide replacement organisms against the day when the parent organism can no longer perform the metabolic functions, etc. The “as we know it” part provides further qualifications: life as we know it here on Earth, it is generally said, exists within thus-and-so temperature range (from something above freezing to something below boiling) on a planet where water is widely available and which has an atmosphere made up mostly of oxygen and hydrogen. And so we think we know what life-on-Earth is: dogs and cats, squids and elephants, ferns and algae and redwood trees, kangaroos and wombats and koalas, grasshoppers and ants and butterflies and moths, and a great many other species, including, of course, us.
When science-fiction writers set their stories on other worlds of the universe, most of the beings with which they populate those worlds are patterned after life-as-we-know-it beings of our own world: oxygen-breathers who occupy that climatic comfort zone that lies somewhere between McMurdo Sound at one extreme and Death Valley at the other. That way they can insert human characters who are able to move about on those worlds without great difficulty and have the interesting adventures that science fiction stories are supposed to provide. Thus we get whale-like aliens, squid-like aliens, bear-like aliens, and a lot of aliens who are basically just human beings with corrugated foreheads. (Hello, Commander Worf!)
Of course, many science-fiction stories are populated by life as we don’t know it—the sort of life that might be found on planets with methane-ammonia atmospheres, for example, or on planets where the gravitational pull is seven hundred times what it is here, or where the temperatures go beyond what we consider the habitable limits. I wrote a story once about a species native to Pluto whose blood is the superconductive fluid we call Helium II. The temperature on Pluto is just a couple of degrees above absolute zero, which is fine for creatures with a superconductive metabolic system, but when the sun comes up and the temperatures rise five or six degrees they have to go dormant until that nice superconductive chill returns. And so on, literally ad infinitum: science-fiction writers have invented a vast and ingenious multitude of peculiar critters that live in uncomfortable places.
All well and good, but I want to return today to our own planet, and that convenient phrase, “life as we know it,” so that I can point out that a great many organisms native to this very world do not fall into that category at all—are, in fact, as alien as anything Frank Herbert or E.E. “Doc” Smith or Hal Clement ever conjured up.
The first ones that come to mind are the anaerobes: primitive creatures, mainly bacteria but nothing more complex than worms, for whom oxygen is poisonous. This unfortunate trait makes life on Earth difficult for anaerobes, of course, because oxygen is practically everywhere; but they have, nevertheless, managed to find niches for themselves in certain very bleak soils and in oceanic mud, among other disagreeable places. There they conduct their miserable little lives, absorbing such foodstuffs as they are able to metabolize in the absence of oxygen, deriving energy from them, and carrying out their reproductive processes in order to bring forth new generations of anaerobes upon the face of the Earth.
Since Earth is an oxygen-rich planet, what are these creatures doing here at all? One theory is that they are degenerate forms of normal oxygen-loving species that were modified by evolutionary pressures to live in oxygen-poor environments and eventually in environments that had no oxygen whatever. That makes some sense, at least to those of us who put credence in Darwinian theory. (This magazine has some readers of the other kind, as I have discovered by getting irate letters from them.) But in 1927 the brilliant biologist J.B.S. Haldane proposed a far more ingenious explanation for the existence of anaerobic organisms: the original atmospheric mix of most planets, he suggested, is mostly hydrogen, ammonia, and methane, and the development of an oxygen-based atmosphere on our world was a relatively late event, the result of the breakdown of the primordial methane and ammonia into carbon, hydrogen, and nitrogen through the action of ultraviolet light from the sun, and the release of oxygen through photosynthesis once chlorophyll-bearing plants evolved. Therefore, Haldane suggested, anaerobic life-forms would have been the default mode on Earth until an oxygen atmosphere appeared. At that point aerobic life began to evolve, and the anaerobic beings that survive today are surviving vestiges of that long-vanished oxygen-free world of Earth’s early days.
These oxygen-shunning inhabitants of Earth seem almost ordinary, however, compared with some of the really strange items with which we share our planet—beings that routinely put up with such hostile living conditions that they seem to have wandered into our world out of the pages of this magazine. Extremophiles is what scientists call them.
Let’s take a look at a few.
Here, for example, is Deinococcus radiodurans, a small pink organism that has been nicknamed “Conan the Bacterium.” Scientists who were experimenting with the use of hard radiation as a food preservative in 1956 noticed an odd bulge in one of their experimental cans of horsemeat, and when they opened it they found that a colony of unfamiliar pink bacteria had established itself inside. Deinococcus wasn’t simply untroubled by the radiation that was bombarding it; it seemed to thrive on it, as Popeye the Sailor does on spinach.
Where did this hardy little bug come from? Some theorists suggested that it had drifted in from space, where radiation levels are far higher than they are on Earth. Others offered a version of the old Haldane notion: in its earliest days, they said, the Earth had been highly radioactive, and Deinococcus was a survivor of that primeval era. The issue remains unresolved.
But here was a creature, anyway, that had an astonishingly high tolerance for radiation. Perhaps, it was suggested, Conan the Bacterium could be put to work devouring nuclear waste, of which a vast amount has been piling up at our various atomic plants. Unfortunately, though it had no trouble with hard radiation, it was unable to cope with such toxic chemicals as toluene that are usually found in nuclear waste. And so, in 1997, Department of Energy researchers produced “Super Conan,” a genetically modified super-Deinococcus that eats vile chemicals just as casually as it does the hard stuff. So far, though, Super Conan has not been released into the environment, because no one is sure what else it might eat, and the current public attitude toward genetically modified organisms is not supportive of indiscriminate distribution of such entities.
An even more awesome extrem-ophile is Kineococcus radiotolerans, well named, for it is radiotolerant indeed. This one turned up at the Department of Energy’s Savannah River Site in South Carolina, once used in the production of hydrogen bombs, where an awkward quantity of radioactive waste has piled up—thirty-five million gallons of it in forty-nine underground storage tanks of uncertain sturdiness. The conventional way of getting rid of this stuff, involving chemical treatments administered by robots, might cost as much as $260 billion. About a decade ago Savannah Site researchers who were looking for some cheaper way of detoxifying the place noticed a slimy substance growing on the end of a rod in one of the tanks of nuclear waste, extracted it using robot arms, and discovered it to be a clump of bacteria capable of withstanding a dose of radiation fifteen times as strong as one that would be fatal to humans.
Not only is Kineococcus happy to make its home in a hellish brew of radioactives that would melt kryptonite, but further experimentation has shown it to be willing and able to feed on industrial solvents, herbicides, chlorinated compounds, and a great many other toxic chemicals, breaking their toxic components down and rendering them harmless. The Savannah Site scientists are now considering breeding Kineococcus in quantity and injecting it into the tanks of nuclear waste and also into the areas around the Hanford, Washington, nuclear plant where leaking storage tanks have contaminated eighty square miles with radioactivity.
Not immediately, of course. Caution prevails. One might think that an environment populated by Kineococcus could only be an improvement on one full of radioactivity. But one never knows. At the moment, 20 percent of the bacterium’s genetic structure involves “unknown functions,” say the researchers, and they want to know more about those before whipping up any substantial supply of the microbe.
How these creatures survive in such unforgiving environments is still pretty much of a mystery. A good jolt of radiation smashes up their genetic structures the same way it would smash up yours or mine, but the big difference is that extremophiles somehow put themselves back together within a few hours.
For those of us—a large majority of the population, I would guess—who are not charmed by the presence of deposits of toxic wastes among us, these hardy microbes hold out hope of eventual cleanup with a minimum of noise and fuss, and at relatively little expense. But the existence of extremophiles sends a second message that’s of particular interest to science fiction readers. It’s a message about the adaptability and durability of living things. (Other extremophiles are found in the chilly plains of Antarctica, on mountain peaks, within volcanoes, and in the depths of the sea.) We live in a huge universe full of worlds, and most of those worlds, very likely, offer environmental conditions very different from those of Earth. But if, here on Earth where we live life as we know it, there are extremphiles in our midst that can survive in surroundings that we would regard as unthinkably user-unfriendly, then surely those other worlds, those worlds of ammonia-methane atmosphere or 700-G gravitational pull, may well have evolved creatures just as alive as me and thee who feel totally comfortable under the alien-to-us conditions there.
Our own extremophiles are just itty-bitty bacteria. But, of course, they occupy small and very special environmental niches on our world. On another world where extreme conditions are the norm, the entire planetary population will be made up of beings who have adapted to those conditions. And my bet is that they won’t just be microbes, either.
