By Joel Achenbach
Sunday, July 29, 2007
If we encountered alien life, would we recognize it? I don't mean large, ambulatory, tentacle-snapping organisms with eyeballs on the ends of stalks. Those are always obvious. I'm talking about the low-key, chilled-out microscopic life-forms that might be lurking below the surface of Mars, or beneath the crust of one of Jupiter's jumbo moons, or in some such exotic, slightly scuzzy planetary environment where you'd definitely never find a Starbucks.
What are we looking for, exactly, when we search for alien life? What is life?
That's the cosmic question pondered in a new report from the National Research Council, "The Limits of Organic Life in Planetary Systems." For more than five years, a committee of scientists tried to imagine what life-as-we-don't-know-it might be like. The conclusion: Life may exist in forms completely unlike anything we see on Earth. We need to keep our minds open to the possible existence of Weird Life.
You're thinking: Yes, and he works down the street at the video store. But even if this seems a bit silly, it's a big question, and a practical one. Our space program spends billions of dollars trying to figure out where life might be hiding in the solar system. Where do we look? The new report says that, in addition to exploring Mars, we may want to take a closer look at Titan, the huge moon of Saturn where pools of liquid hydrocarbons might contain Weird Life; and Saturn's moon Enceladus, which has geysers of water ice and water vapor shooting through its crust.
Even more provocative is the hypothesis advanced by scientist and author Paul Davies, that there may have been a "second origin" of life on Earth -- or many origins. Weird Life, in fact, may exist right now, on Earth, in what Davies calls a "shadow biosphere." We just haven't figured out how to look for it.
"It could be under our noses, or even in our noses," Davies told me. "The world is teeming with microbes -- squillions and squillions of them. The vast majority of which haven't been characterized, much less had their genome sequenced. We don't know what they are. And some of those might be shadow life."
Michael Meyer, lead scientist for NASA's Mars program, agrees: "Our capabilities of looking in the microbial world are still pretty crude. We have marvelously sensitive techniques for finding what we've found before."
Time to take another look under the sofa cushions.
All life as we know it has emerged through Darwinian natural selection. Evolution isn't simply something that happens to life after life gets rolling. NASA's official definition of life is that it's a "self-sustained chemical system capable of undergoing Darwinian evolution." But in the future it may be possible, the new report says, to manipulate human life so that it evolves via Lamarckian, as opposed to Darwinian, processes.
Jean-Baptiste Lamarck was an 18th-century French naturalist and early proponent of the notion of evolution. He proposed the idea, now discredited, of the "inheritance of acquired characteristics," in which attributes and talents gained during one's life could be passed on to one's heirs. Maybe he was just ahead of his time: "Humankind will be able to perceive and solve problems in human biology," the new report reads, "without needing to select among random events, thus sparing the species the need to remove unavoidable genetic defects through the death of individuals."
Every biologist would love to find even a scrap of extraterrestrial (or weird) life, because right now we have only a single example of biochemistry. We don't know the "rules" of organic chemistry, says John Baross, a University of Washington biologist and the lead author of the report.
That said, it's very hard to imagine an organism that wouldn't take advantage of the unusual properties of carbon and water. Carbon is great for making complicated three-dimensional structures -- a protein, say, or a DNA molecule. When we study the universe through telescopes, we see the tell-tale spectroscopic signatures of carbon molecules everywhere. Our cosmos has a hankering to do carbon chemistry. All life on Earth is carbon-based.
Water, meanwhile, is almost a miracle unto itself -- the perfect solvent, with all kinds of quirky properties that help make life possible. In fact, the report turns that statement on its head: Life on Earth uses molecular structures with properties "specifically suited to the demands imposed by water." Water is in charge. And wherever we go on Earth where there's energy and liquid water -- even miles beneath the surface, or around boiling volcanic vents at the bottom of the sea -- we find life.
More important, perhaps, life as we know it has a rather ordinary streak. All living things use mundane elements, the common stuff found all over the place: carbon, hydrogen, nitrogen, oxygen, phosphorous and sulfur. Life is small-d democratic. Maybe a life form could employ exotic elements such as platinum or uranium, but it doesn't seem necessary. Life doesn't have a taste for couture; it buys everything off the rack.
"It is chemical in essence," the report says of life, a statement that is both bland and mind-boggling. Life, you'd think, would be more than just chemicals interacting. Surely it would require some kind of special juice, energy, force. But no: Vitalism is a theory that died out a long time ago. It's just organic chemistry. It's just reactions involving polymers, covalent bonds, catalysts, solvents, nucleophiles, electrophiles.
The report by Baross and his fellow scientists is ultimately optimistic. It's almost a refutation of the "rare earth" hypothesis -- the argument that habitable planets, blessed with the right mix of elements for life and a long time for that life to evolve, are few and far between. Baross says, "We believe that astrobiology is a science of optimism. We have no idea if life exists elsewhere. We are dedicating our lives to searching for this. Why are we being driven to do this? I think it's such a fundamental question."
Paul Davies reports, "We are still completely in the dark as to whether life is a stupendous chemical fluke that happened once, or whether there is a sort of life principle (or cosmic imperative to use the words of Nobel prizewinner Christian de Duve) at work in the universe. The best (cheapest, easiest) way to settle the debate is to see whether life has started many times over on Earth."
Perhaps the search for life, and Weird Life, offers a good lesson for everyone. We all have a bad habit of tending to see only the things we expect to see. We are innately biased in favor of the familiar. "The human mind finds it difficult to create ideas truly different from what it already knows," the report states.
So look around: Do you see the world as it really is, or as you think it's supposed to be? Can you see -- with your big eyes and big brain -- what's really happening all around you?
Maybe we've found the Weird Life, and it is us.
Joel Achenbach is a Washington Post staff writer and blogs at washingtonpost.com/achenblog.