"These comets are thought to contain some of the most primitive material in the solar system, more or less unchanged since its formation," Scott A. Sandford, a NASA research astrophysicist and co-investigator of the Stardust mission, told me one afternoon this past spring. We sat talking in the dining area of a huge white plastic tent pitched in the middle of the NASA Ames Research Center campus in Moffett Field, Calif., a tree-dotted, 440-acre sprawl of tan brick laboratory buildings.
"Among the things we'll want to know about the material we've collected," continued Sandford, a stout, rugged-looking man with a way of talking about even the most far-flung, wondrous endeavors as though he were a plumber discussing your bathroom pipes, "is what fraction of it is organic, what kinds of organics they are and what possible role they may have played in life's emergence on earth."
Searching for the origins of life in the dust of a comet might sound like a bit of cosmically cockeyed indirection, something straight out of a New Age sci-fi novel. The Stardust mission, however, is typical of a number of projects to divine life's origins, all part of a $75-million-a-year scientific enterprise now being financed by NASA. It is known as astrobiology.
The appellation invokes images of ferns in outer space, or interstellar swamps, but these are mundane imaginings compared with the various avenues of exploration being pursued by astrobiologists. There are projects like drilling into the earth's boiling-hot deep-sea vents or icy dark Antarctic waters in order to do DNA analysis of primitive life forms. Or trying to replicate in the laboratory the moment when the chemical earth first transformed into a biological one. Or lassoing a multibillion-year-old comet in search of organic compounds like amino acids and carbon, the so-called building blocks of life.
First conceived of by a group of NASA scientists back in the mid-90's, the NASA Astrobiology Institute has since evolved into a global enterprise: a partnership between NASA and 16 research teams based at universities and institutes around the country, plus a number of international consortia. Many of the world's roughly 2,000 astrobiologists and other scientists also flock to the biannual Astrobiology Science Conference, the most recent one held at the NASA Ames Research Center.
Seated around Sandford under the main tent of the astrobiology conference this past spring were scientists from all across the globe, representing a dizzying array of disciplines. A partial list would include biologists, microbiologists, physicists, astrophysicists, theoretical biophysicists, chemists, organic chemists, geologists, bio-geo-chemists, paleontologists, paleobotanists and astronomers. And yet they were all there as like-minded pilgrims, devoted to astrobiology's core mission of answering the three fundamental questions of our existence. To quote from the cover of NASA's official astrobiology time line, which begins some 15 billion years ago with the Big Bang and shows no other demarcation until the formation of our solar system some 11 billion years later: "Where do we come from? Are we alone? Where are we going?"
These are compelling times we live in. Around the world, wars are being fueled by fundamentalist adherence to ancient creeds. Here in the United States, where religious fervor has in many ways never been stronger, creationism still finds its way into some classrooms, and biblically accurate creation theme parks are built, with scripture accompanying dinosaur-bone displays. And yet all the while, the United States government is allotting millions of dollars each year to the global endeavor of piecing together from an ever-growing body of evidence the actual story of creation.
"The whole movement arose back in the mid-1990's," recalls David Morrison, a NASA scientist and one of astrobiology's founders. "We were looking at that time to alter our focus in some way, and we suddenly realized that we had a whole lot of new science and technology that could be brought to bear on the question of the origin, evolution and distribution of life, everything from the recent discovery of planets around other stars to the human genome project to our forthcoming missions to Mars."
There was a time -- right up until the early 1950's, in fact -- when the sorts of questions now being addressed by astrobiology were the stuff of either myth and science fiction, or of only the most marginal, far-fetched or pie-in-the-sky kinds of science. Now, however, we face a strangely reverse reality: the state of our knowledge has evolved to the point where our previous conjecturing about life's origin has been exposed as woefully myopic and parochial, not nearly far-fetched or skyward-looking enough. Astrobiology is a science born of a time when it is no longer the prospect of solving the question of life's origins that seems beyond our powers -- it's trying to imagine what a world in which we have done so may be like.
Astrobiology's overall mission includes answering the questions of whether life exists elsewhere and what life's overall prognosis on earth and beyond might be. The answers to those two queries, however, pivot around science's holy grail: divining the origin of life in the universe. It is a quest that is being pursued from three directions: comparative analysis of DNA on earth; biochemical synthesis of life in the lab, or "test-tube evolution"; and, finally, examination of the various organic compounds that exist in the depths of outer space -- perhaps the ideal laboratory, because of both its deep history and inherent lack of contamination.
Of astrobiology's three approaches, the first, DNA analysis, is perhaps the most traditional mode of inquiry, or at least the most grounded. Precisely because all life forms are made of the same stuff, are all so-called "DNA-protein-based organisms," scientists can now use comparative DNA analysis to trace the common roots of life's collective family tree further back than ever imagined.
"I like to use the comparison of tracing the phylogeny of languages," says Antonio Lazcano of the National Autonomous University of Mexico, a featured speaker at the astrobiology conference. "Suppose we want to trace the roots of the Romance languages like French, Italian, Spanish, etc. It is clear that they all diverge from the Latin spoken, for example, by Roman soldiers in the different regions of Europe. Now, we know Latin is a very ancient language. But we would hardly say that it is a primitive one. So the question then becomes what came before that."
As with any language tree, the further back in time you attempt to go with it, the more the base starts to break into those root utterances from which all modern languages emanate. After a point, the derivations and linkages have to be more or less intuited. And yet with the life-tree puzzle that astrobiology is now putting together, even the still-to-be assembled pieces are stunning both for the expanse of time they represent and the undeniable, if unlikely and to some objectionable, linkages they establish.
There is, for example, a consensus now about the existence and the essential character of life's common ancestor, the great, great, great (to the power of a gazillion) grandparent of you and me and everything else that we see (or can't see) living around us. It even has a name: LUCA, or Last Universal Common Ancestor, although some prefer the name Cenancestor, from the Greek root "cen" (meaning "together") and others favor LCA, or Last Common Ancestor.
There is very little known about LUCA, though scientists currently agree on two things. One, that it had to have existed. And two, that it had to have been extremely rugged. As recently as the mid-70's there were thought to be only two domains of life on earth: the prokaryotes -- small, single-celled bacteria lacking a nucleus or other complex cellular structures; and the eukaryotes -- organisms made of one or more cells with a nucleus, a category embracing everything from complex multicellular entities, like mammals, reptiles, birds and plants, to the single-celled amoeba.
In 1977, however, a molecular biologist from the University of Illinois named Carl Woese identified within the prokaryotes a genetically distinct class of bacteria now known as the archaea, many of them primitive, single-celled organisms known as "extremophiles" because they live in extreme environments like volcanic vents or Antarctic waters. When the DNA of archaea was compared with that of prokaryotes and eukaryotes, it became clear that the trifurcation of life from LUCA occurred far earlier than previously believed, well over three billion years ago, when there was little or no oxygen in the earth's atmosphere.
LUCA, in other words, had to have been a hard-bitten little extremophile of some kind or other. And while the debate rages as to precisely what sort of entity this common ancestor was, and which of the three current domains it was more kindred to, scientists have now discovered a variety of examples of what it might have been, now thriving all over the earth -- decidedly uncuddly, extremophilic creatures sometimes called superbugs. There are, for instance, the acidophiles -- bacteria that have been found to thrive on the gas given off by raw sewage and that both excrete and multiply in concentrations of acid strong enough to dissolve metal and destroy entire city sewer systems. At the opposite end of the spectrum, there are superbugs that live in temperatures below -320 degrees Fahrenheit, lower than that of liquid nitrogen.
Still, it turns out that some of the clearest, and certainly the most stunning, evidence of LUCA's former existence and of our inextricable bond with it, is literally right beneath our noses, within each of our body's cells, in the form of so-called living fossils. DNA analysis of the distinct organisms, or organelles, that live inside and help govern the various functions of our body's cells -- the nucleus, the mitochondria, the flagella and so on -- has revealed a direct genetic link between these organelles and the primordial earth's earliest extremophilic bacteria.
Somewhere along the line, in other words, but certainly very early on, these fully independent, single-celled primordial superbugs and their specialized functions got co-opted, in a kind of primitive symbiosis, into the greater service of the more secure, membrane-bound, multitasking complex that would become the eukarytic cell and its subsequent multicellular manifestations, most prominent among these (at least in our minds) being ourselves. You and I, and the darting birds, and the windswept tree boughs, carry around with each of us the living remnants of our own and all life's fiery origins.
As far along the path toward origins as the analysis of DNA on earth has already led us, many astrobiologists say it isn't nearly far enough. Indeed, an entity like LUCA, for all its mysteries, is generally considered to be something eminently knowable, a relative latecomer in life's story, which must have had a fairly sophisticated genome to have survived the extreme conditions of the early earth. If LUCA is the common ancestor of life as we currently recognize it, the big question is: What came before that?
Many scientists now argue that before LUCA and the emergence of our current DNA-protein world, there was what's referred to as an RNA world, one made up only of rudimentary RNA-based entities that were later subsumed into RNA's current role as our DNA's messenger. And before the RNA-world, there has to have been what might be described as the real prize for astrobiologists, the so-called first living organism, or FLO.
FLO may not even be an entity so much as a moment, the very one, in a sense, that countless alchemists over the centuries -- and later, scientists -- have tried to isolate. Many credit Stanley Miller with starting the modern science of origins when, back in the fall of 1952, as a young graduate student in chemistry at the University of Chicago, he electrically charged in his lab a flask-bound rendition of the earth's early atmosphere and produced amino acids. Miller's primordial soup ingredients have since been reconfigured, and his results somewhat diluted by the revelation that amino acids can be not only easily synthesized in the lab but also even found floating in outer space. And yet his experiment catalyzed the current search for that moment when "being" began, when chemicals and crude organic compounds somehow culminated in a first living thing.
In order to find FLO, astrobiologists must first arrive at a working definition of "living." "It all depends on what we mean by biology," says Jeffrey Bada, a geochemist at the Scripps Institution of Oceanography at U.C. San Diego. "For me, I would say that all you need to define life is imperfect replication. That's it. Life. And what that means is that the entity can make copies of itself but not exact copies. A perfectly replicating system isn't alive because it doesn't evolve. Quartz crystals make exact copies of themselves and have done from the beginning of the earth. They don't evolve, however, because they're locked into that particular form. But with imperfect replication you get mutants that develop some sort of selective advantage that will allow them to dominate the system. That whole system then evolves, and you get this cascade of evolution progressing to more complicated entities. But something preceded all that, something that could do this basic thing of replication and mutation, and that's what everyone is trying to figure out."
What is known about FLO is that for it to have happened at all, it had to have been an even tougher entity than LUCA was merely to overcome the universe's most prohibitive law, the second law of thermodynamics, which dictates that all matter tends toward entropy, the dissipation of energy. All life is in utter defiance of that law, a bound, energy-gathering stay, however brief, against entropy.
The other essential requirement for the kind of imperfect replication system that Bada describes is that there had to have been a first bit of information, some kind of biochemical message, or code, however crude, to begin to convey. Or, in this case, to misconvey, the whole story of life's emergence and evolution on earth being, in essence, a multibillion-year-long game of telephone, in which the initial utterance, the one that preceded all others, was increasingly transmuted and reinvented the further along it was passed. It is the precise nature of that first utterance that astrobiologists are trying to decipher.
"There are some people," Bada says, "who would argue quite vigorously with me about whether the simple kind of replicators I speak of qualify as life. Others would argue that even the sorts of simpler catalytic, self-sustaining reactions that occur on mineral surfaces are living, or are the first type of living system, without even the requirement for genetic information. But to me that's still chemistry, not life. Or it's life as we don't know it."
A number of chemists are now trying to recreate in their labs at least a rough approximation of this elusive and somewhat ill-defined transition from the purely chemical to the biological, searching for the mix of ingredients which in their interaction create ever more complex molecules in a recurring series of feedback loops that eventually culminate in a self-replicating system that soon dominates its environment. Gerald Joyce, a colleague of Bada's at U.C. San Diego, and one of the pioneers of test-tube evolution, has managed to achieve such a synthesis in his lab using a random mixture of RNA molecules. Jack Szostak of the Harvard Medical School, meanwhile, has been doing groundbreaking work in his lab with organic compounds known as amphiphiles -- compounds that have been shown to produce in water cell-like structures known as vesicles, the ideal sort of contained microenvironment that the earliest living entity on earth might have needed to get started.
"I'm going to stick my neck out here," Bada says, "but I'd be surprised, very surprised, if in the next 5 or 10 years somebody somewhere doesn't make a molecular system that can self-replicate with very little interaction on our part. You just give it the proper chemicals and it starts churning away and replicates and growing and soon dominates the system."
Steven Benner, a test-tube evolutionist working with a team of researchers at the University of Florida, may soon be closing in on that elusive alchemy. "We're not quite at origins yet," he says. "My goal now is 100 percent focused on getting a self-replicating system, to make synthetic life. It won't get us the absolute answer to the question of origins, but it could give us a model, a framework for understanding how certain pathways that led to life evolved."
The search for the origins of life in synthetic life is, as Benner puts it, like the proverbial drunk looking for his keys under the lamppost, even though he knows he lost them by the door, because the light is better under the lamppost. But perhaps -- as poets and lovers have long maintained -- the light is best out under the stars. The early earth is now thought to have had a number of different atmospheres over the long course of its coalescence, the most likely was a rather bland mix of nitrogen and carbon dioxide, one not highly conducive to the production of amino acids. Meanwhile, amino acids have been discovered just about everywhere, including inside meteorites and, evidence suggests, drifting about in the so-called interstellar medium.
Along with carbon and a number of other organic compounds essential to life, amino acids seem to have come along with the universe's original package, woven into the very fabric of our solar system and perhaps long before that, hailing from somewhere out there in that vast 10-billion-year lacuna between the Big Bang and the earth's debut. In the words of Jill Tarter, an astrobiologist at the SETI Institute: "Every atom of iron in our blood was produced in a star that blew up about 10 billion years ago." What those searching the heavens for the answer to life's origins are trying to decipher is how these seemingly prepackaged ingredients for life actually became life, and whether our planet could possibly have been the only viable egg in the universe's sack.
Even the decidedly low-key Sandford starts twisting in his seat like an excited kid on Christmas morning when he thinks about the return of the Stardust capsule in January 2006, and the possible secrets buried therein. Once the material is recovered, certain tests conducted on whatever organic compounds are found will both certify their extraterrestrial origin and perhaps ultimately help to determine their approximate age in relation to the formation of our solar system and of the earth.
"We want to try to get a real sense of what kinds of building blocks are out there that arrive on planets on Day 1 of their formation," says Sandford. "Of course, since we don't know how exactly life got started, it's hard to assess how critical each compound is. Even if life is an inevitable byproduct of stuff falling out of the sky, certain key aspects of life's formation may also be dominated by indigenous activity on a given planet. Life may have had to beg and borrow and steal everything it could get to happen, and so why be picky? For a long time the argument about origins has been an either-or type of thing: life either happened with a bolt of lightning to the early atmosphere or it was the opposite extreme of actual bugs falling out of the sky and seeding the earth. The truth probably falls somewhere in the middle of that."
While the Stardust mission stands to provide invaluable insights, the successful gathering of a comet's dust is a dazzling achievement in and of itself. The interlude with the comet Wild 2 was timed for its approach to the sun, which rapidly warmed up the comet's ices, causing dust and gas to blow off the comet's surface in a vaporous halo, or "coma." The Stardust spacecraft flew through that coma at approximately 4 miles a second. As it did, a tennis racket-like device on the craft known as an "aerogel impact collector" reached up and absorbed the comet's dust, then folded down against a metal plate to be enveloped by the chambers of the nautilus shell.
After the capture -- verified by on-board instruments -- the Stardust drifted into the outer asteroid belt, and will be nearly another year and a half getting back to us. As it approaches the outer rim of the earth's atmosphere on the morning of Jan. 15, 2006, it will release the Stardust capsule for re-entry and then skip off forever into outer space, its mission accomplished.
At once the draw and the inevitable drawback of a science with a scope as vast as astrobiology's is that it precludes a good many of its very practitioners from seeing out their own most inspired visions. While Sandford awaits the Stardust capsule's return, a number of other astrobiological starcombers have their sights and hopes set on a mission the results of which neither they nor many of us alive today will be around to witness: landing upon and drilling into Jupiter's moon Europa.
About the size of the earth's moon, Europa is covered by ice roughly 6 miles deep, beneath which is 30 to 60 miles of water, roughly the same volume as that of the earth's oceans. While water is often thought to be synonymous with life, Europa is totally dark, ruling out any form of photosynthesis, and thus life as we understand it. There is also thought to be little or no communication between the underlying ocean and Europa's surface. All of which makes the prospect of discovering any signs of life there almost unbearably enticing to astrobiologists.
"I'd love nothing more than for us to find a thriving RNA world there," says Bada. "We can try to reconstruct that in a lab, but if we had a natural example of it, that would be fantastic. We'd have a picture of what life may have been like on earth before it evolved into the modern protein-DNA world of today. Of course, it's hard to imagine the kind of environment that's on Europa producing organisms that look anything like the biochemistry we have here, either modern or LUCA-type organisms. And that's what I find fascinating. Here we could have a completely independent form of life, even though the chemistry leading up to it might be universal. Now, I don't expect little green men to crawl out of the ocean there, but I wouldn't be a bit surprised if we didn't see some extremely interesting chemistry involved in some of the very stages that led to replicating entities here on earth."
The first stage of NASA's Europa project is a 20-year mission to orbit and photograph the moon, and that is not set for launching until 2015. As for the landing and drilling stages of the project, if they come to pass at all, they will occur much further down the line, "for the next generations," as Bada puts it, "the kids that aren't even born yet."
Whatever clues Europa's watery depths might yield -- or Mars's rocks, or the detritus of Wild 2, or the fiery and frigid recesses of our own planet, for that matter, and the yet-unknown twists and turns of our own DNA -- the sense now is that we, or at least the kids that aren't even born yet, are in for a whole new way of seeing. It's fine but ultimately facile to believe that solving the mystery of life's origins would help to solve anything else about our lives -- to draw our collective focus away from fundamentalist or nationalist fervor, for example, or from anyone's claim to higher authority or birthright, all births having been definitely traced back to a natural brand of fire and brimstone more fearsome than that found in any book. It would be nonsensical to think that, even in our own little patch of time, an almost unfathomable sense of collective liberation and comfort could be found from being able to look up at the stars at night and see not the constellations of old, but at once the beginning and the future of all existence, the ongoing impulse, if not the sound itself, of life's initial utterance.
Still, what science has already revealed to us about our own biology's inward microcosm should both give us pause and offer us new paradigms. The cell, for example, is at once a very apt metaphor and cautionary tale for civilization, with its long history of microorganisms forged in a primordial hellfire and then gathered inside protective outer walls for the sake of greater cooperation and complexity.
"Things are in the saddle,/And ride mankind," Ralph Waldo Emerson wrote in
a poem warning against the soul-withering effects of civilization's excesses.
Knowing what we do now, however, about life's beginnings, the word "things"
takes on a whole new meaning. And should our internal extremophiles eventually
ride or override us (as human behavior sometimes suggests they are doing) into
recreating the very fires from which they first emanated, there is, perhaps,
some comfort to be found in astrobiology's revelation that our own rugged
ancestors will be around to inherit this earth and start the entire cycle over again.
Charles Siebert is a contributing writer for the magazine and the author,
most recently, of "A Man After His Own Heart: A True Story."
Charles Siebert is a contributing writer for the magazine and the author, most recently, of "A Man After His Own Heart: A True Story."
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