Sunday, September 26, 2004

Asking the big questions: Are we alone? What happens to civilizations like our's?

The New York Times Magazine - CHARLES SIEBERT - The Genesis Project

To put it mildly, this is an interest of mine. The most recent discoveries in extrasolar planetary science favor an abundance of earthlike planets (Bayesian reasoning -- they've chopped off the rare-planet end of the probability curve). This biases the hoary Drake Equation towards the likelihood of life, even technological life.

The Genesis Project (love the name the NYT title hack gave it) is about filling out other terms in the Drake Equation. It points in some weird directions. Francis Crick gained a reputation as a fallen genius because of his support for the hypothesis that life on earth arose by deliberate "seeding" of a newly formed planet. The idea was not knew to Crick, cometary seeding of life has been popular in science fiction for generations.

Yet Fermi's Paradox remains -- we don't find godlike aliens underfoot. Which leads to the most interesting question of all -- what happens to technocentric civilizations?
September 26, 2004

...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.

... 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.

... 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.

... 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.

[jf: In other words the extremophile discoveries were (perhaps literally?) earthshattering. They radically changed our thoughts about when life first arose on earch, and drastically narrowed the interval between formation of the planet and the evolution of life.]

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.

[jf: Recent NASA research has isolated bugs that live off the energy from aluminum ions and can survive high levels of gamma radiation and probably vacuum. It's likely we've already seeded Mars with some these bugs. Some of these terrestrial (whatever that means) bugs could not be detected by any technology we're likely to put on a space probe.]

... 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.

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 [jf. So really Bada is defining life as a "contained system capable of evolution" -- by that definition the world economy is "alive". I've made the same point -- canopy economics.] 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.

... 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. [jf: This has bothered physicists for a long time. Crick was a physicist by training -- it bothered him. I dimly recall it bothered Neils Bohr, Schrodinger, and their kin.]

... 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.'' [jf. Sounds like a "New Kind of Science"?]

... 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. [jf. I thought the BBC recently reported clouds of simple carbohydrates in extrasolar space, but I can't find the article now. Update: it was a cloud of simple sugar molecules in our galaxy.]

... long 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.''

... 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.''

Phew. A relief from thinking about our negligent and incompetent government!

A parting thought. If it turns out that the fundamental physics of the universe predispose to a cloud of life forming soup infesting all of space, what does that say about the "design" of the universe? And Fermi's Paradox?

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