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them up in a lab； 脿 la stanley miller and haroldurey； but the universe does it readily enough。 lots of molecules in nature get together to formlong chains called polymers。 sugars constantly assemble to form starches。 crystals can do anumber of lifelike things鈥攔eplicate； respond to environmental stimuli； take on a patternedplexity。 they鈥檝e never achieved life itself； of course； but they demonstrate repeatedly thatplexity is a natural； spontaneous； entirely monplace event。 there may or may not be agreat deal of life in the universe at large； but there is no shortage of ordered self…assembly； ineverything from the transfixing symmetry of snowflakes to the ely rings of saturn。
so powerful is this natural impulse to assemble that many scientists now believe that lifemay be more inevitable than we think鈥攖hat it is； in the words of the belgian biochemist andnobel laureate christian de duve； 鈥渁n obligatory manifestation of matter； bound to arisewherever conditions are appropriate。鈥潯e duve thought it likely that such conditions would beencountered perhaps a million times in every galaxy。
certainly there is nothing terribly exotic in the chemicals that animate us。 if you wished tocreate another living object； whether a goldfish or a head of lettuce or a human being； youwould need really only four principal elements； carbon； hydrogen； oxygen； and nitrogen； plussmall amounts of a few others； principally sulfur； phosphorus； calcium； and iron。 put thesetogether in three dozen or so binations to form some sugars； acids； and other basicpounds and you can build anything that lives。 as dawkins notes： 鈥渢here is nothingspecial about the substances from which living things are made。 living things are collectionsof molecules； like everything else。鈥�
the bottom line is that life is amazing and gratifying； perhaps even miraculous； but hardlyimpossible鈥攁s we repeatedly attest with our own modest existences。 to be sure； many of thedetails of life鈥檚 beginnings remain pretty imponderable。 every scenario you have ever readconcerning the conditions necessary for life involves water鈥攆rom the 鈥渨arm little pond鈥�
where darwin supposed life began to the bubbling sea vents that are now the most popularcandidates for life鈥檚 beginnings鈥攂ut all this overlooks the fact that to turn monomers intopolymers （which is to say； to begin to create proteins） involves what is known to biology as鈥渄ehydration linkages。鈥潯s one leading biology text puts it； with perhaps just a tiny hint ofdisfort； 鈥渞esearchers agree that such reactions would not have been energeticallyfavorable in the primitive sea； or indeed in any aqueous medium； because of the mass actionlaw。鈥潯t is a little like putting sugar in a glass of water and having it bee a cube。 itshouldn鈥檛 happen； but somehow in nature it does。 the actual chemistry of all this is a littlearcane for our purposes here； but it is enough to know that if you make monomers wet theydon鈥檛 turn into polymers鈥攅xcept when creating life on earth。 how and why it happens thenand not otherwise is one of biology鈥檚 great unanswered questions。
one of the biggest surprises in the earth sciences in recent decades was the discovery ofjust how early in earth鈥檚 history life arose。 well into the 1950s； it was thought that life wasless than 600 million years old。 by the 1970s； a few adventurous souls felt that maybe it wentback 2。5 billion years。 but the present date of 3。85 billion years is stunningly early。 earth鈥檚surface didn鈥檛 bee solid until about 3。9 billion years ago。
鈥渨e can only infer from this rapidity that it is not 鈥榙ifficult鈥櫋or life of bacterial grade toevolve on planets with appropriate conditions；鈥潯tephen jay gould observed in the new yorktimes in 1996。 or as he put it elsewhere； it is hard to avoid the conclusion that 鈥渓ife； arising assoon as it could； was chemically destined to be。鈥�
life emerged so swiftly； in fact； that some authorities think it must have had help鈥攑erhapsa good deal of help。 the idea that earthly life might have arrived from space has a surprisinglylong and even occasionally distinguished history。 the great lord kelvin himself raised thepossibility as long ago as 1871 at a meeting of the british association for the advancement ofscience when he suggested that 鈥渢he germs of life might have been brought to the earth bysome meteorite。鈥潯ut it remained little more than a fringe notion until one sunday inseptember 1969 when tens of thousands of australians were startled by a series of sonicbooms and the sight of a fireball streaking from east to west across the sky。 the fireball madea strange crackling sound as it passed and left behind a smell that some likened to methylatedspirits and others described as just awful。
the fireball exploded above murchison； a town of six hundred people in the goulburnvalley north of melbourne； and came raining down in chunks； some weighing up to twelvepounds。 fortunately； no one was hurt。 the meteorite was of a rare type known as acarbonaceous chondrite； and the townspeople helpfully collected and brought in some twohundred pounds of it。 the timing could hardly have been better。 less than two months earlier；the apollo 11 astronauts had returned to earth with a bag full of lunar rocks； so labsthroughout the world were geared up鈥攊ndeed clamoring鈥攆or rocks of extraterrestrial origin。
the murchison meteorite was found to be 4。5 billion years old； and it was studded withamino acids鈥攕eventy…four types in all； eight of which are involved in the formation of earthlyproteins。 in late 2001； more than thirty years after it crashed； a team at the ames researchcenter in california announced that the murchison rock also contained plex strings ofsugars called polyols； which had not been found off the earth before。
a few other carbonaceous chondrites have strayed into earth鈥檚 path since鈥攐ne that landednear tagish lake in canada鈥檚 yukon in january 2000 was seen over large parts of northamerica鈥攁nd they have likewise confirmed that the universe is actually rich in organicpounds。 halley鈥檚 et； it is now thought； is about 25 percent organic molecules。 getenough of those crashing into a suitable place鈥攅arth； for instance鈥攁nd you have the basicelements you need for life。
there are two problems with notions of panspermia； as extraterrestrial theories are known。
the first is that it doesn鈥檛 answer any questions about how life arose； but merely movesresponsibility for it elsewhere。 the other is that panspermia sometimes excites even the mostrespectable adherents to levels of speculation that can be safely called imprudent。 franciscrick； codiscoverer of the structure of dna； and his colleague leslie orgel have suggestedthat earth was 鈥渄eliberately seeded with life by intelligent aliens；鈥潯n idea that gribbin calls鈥渁t the very fringe of scientific respectability鈥濃�攐r； put another way； a notion that would beconsidered wildly lunatic if not voiced by a nobel laureate。 fred hoyle and his colleaguechandra wickramasinghe further eroded enthusiasm for panspermia by suggesting that outerspace brought us not only life but also many diseases such as flu and bubonic plague； ideasthat were easily disproved by biochemists。 hoyle鈥攁nd it seems necessary to insert areminder here that he was one of the great scientific minds of the twentieth century鈥攁lsoonce suggested； as mentioned earlier； that our noses evolved with the nostrils underneath as away of keeping cosmic pathogens from falling into them as they drifted down from space。
whatever prompted life to begin； it happened just once。 that is the most extraordinary factin biology； perhaps the most extraordinary fact we know。 everything that has ever lived； plantor animal； dates its beginnings from the same primordial twitch。 at some point in anunimaginably distant past some little bag of chemicals fidgeted to life。 it absorbed somenutrients； gently pulsed； had a brief existence。 this much may have happened before； perhapsmany times。 but this ancestral packet did something additional and extraordinary： it cleaveditself and produced an heir。 a tiny bundle of genetic material passed from one living entity toanother； and has never stopped moving since。