16 LONELY PLANET

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    IT ISN’T EASY being an anism. In the whole universe, as far as we yet know, there isonly one place, an inspicuous outpost of the Milky Way called Earth, that will sustain you,and even it  be pretty grudging.

    From the bottom of the deepest o trench to the top of the highest mountain, the zo covers nearly the whole of known life, is only something over a dozen miles—not muchwhe against the roominess of the os at large.

    For humans it is even worse because en to belong to the portion of living thingsthat took the rash but venturesome decision 400 million years ago to crawl out of the seas andbee land based and oxygehing. In sequeno less than 99.5 pert of theworld’s habitable space by volume, acc to oimate, is fually—in practicalterms pletely—off-limits to us.

    It isn’t simply that we ’t breathe in water, but that we couldn’t bear the pressures.

    Because water is about 1,300 times heavier than air, pressures rise swiftly as you desd—by the equivalent of omosphere for every teers (thirty-three feet) of depth. On land,if you rose to the top of a five-hundred-foot eminence—Cologhedral or the WashingtonMo, say—the ge in pressure would be so slight as to be indisible. At the samedepth uer, however, your veins would collapse and your lungs would press to theapproximate dimensions of a Coke . Amazingly, people do voluntarily dive to such depths,without breathing apparatus, for the fun of it in a sport known as free diving. Apparently theexperience of having your internal ans rudely deformed is thought exhilarating (though notpresumably as exhilarating as having them return to their former dimensions uponresurfag). To reach such depths, however, divers must be dragged down, and quite briskly,by weights. Without assistahe deepest anyone has gone and lived to talk about itafterward was an Italian named Umberto Pelizzari, who in 1992 dove to a depth of 236 feet,lingered for a nanosed, and then shot back to the surface. In terrestrial terms, 236 feet isjust slightly over the length of one New York City block. So even in our most exuberantstunts we  hardly claim to be masters of the abyss.

    anisms do of course mao deal with the pressures at depth, though quite howsome of them do so is a mystery. The deepest point in the o is the Mariana Tren thePacific. There, some seven miles down, the pressures rise to over sixteen thousand pounds persquare inch. We have managed once, briefly, to send humans to that depth in a sturdy divingvessel, yet it is home to ies of amphipods, a type of crusta similar to shrimp buttransparent, which survive without any prote at all. Most os are of course muchshallower, but even at the average o depth of two and a half miles the pressure isequivalent to being squashed beh a stack of fourteen loaded t trucks.

    Nearly everyone, including the authors of some popular books on oography, assumesthat the human body would crumple uhe immense pressures of the deep o. In fact,this appears not to be the case. Because we are made largely of water ourselves, and water is“virtually inpressible,” in the words of Frances Ashcroft of Oxford Uy, “the bodyremains at the same pressure as the surrounding water, and is not crushed at depth.” It is thegases inside your body, particularly in the lungs, that cause the trouble. These do press,though at oint the pression bees fatal is not known. Until quite retly it wasthought that anyone diving to one hundred meters or so would die painfully as his or her lungsimploded or chest wall collapsed, but the free divers have repeatedly proved otherwise. Itappears, acc to Ashcroft, that “humans may be more like whales and dolphins than hadbeen expected.”

    Plenty else  g, however. In the days of diving suits—the sort that wereected to the surface by long hoses—divers sometimes experienced a dreadedphenomenon known as “the squeeze.” This occurred when the surface pumps failed, leadingto a catastrophic loss of pressure in the suit. The air would leave the suit with such viole the hapless diver would be, all too literally, sucked up into the helmet and hosepipe.

    When hauled to the surface, “all that is left in the suit are his bones and ss of flesh,”

    the biologist J. B. S. Haldane wrote in 1947, adding for the be of doubters, “This hashappened.”

    (Ially, the inal divi, designed in 1823 by an Englishman namedCharles Deane, was intended not for diving but for fire-fighting. It was called a “smokehelmet,” but being made of metal it was hot and cumbersome and, as Deane soon discovered,firefighters had no particular eagero enter burning structures in any form of attire, butmost especially not in something that heated up like a kettle and made them clumsy into thebargain. In an attempt to save his iment, Dearied it uer and found it was idealfor salvage work.)The real terror of the deep, however, is the bends—not so much because they areunpleasant, though of course they are, as because they are so much more likely. The air webreathe is 80 pert nitrogen. Put the human body under pressure, and that nitrogen istransformed into tiny bubbles that migrate into the blood and tissues. If the pressure isged too rapidly—as with a too-quick ast by a diver—the bubbles trapped within thebody will begin to fizz ily the manner of a freshly opened bottle of champagne,clogging tiny blood vessels, depriving cells of oxygen, and causing pain so excruciating thatsufferers are proo bend double in agony—hehe bends.”

    The bends have been an occupational hazard for sponge and pearl divers siimeimmemorial but didn’t attract much attention in the Western world until the eeury, and then it was among people who didn’t get wet at all (or at least not very wet andnot generally much above the ankles). They were caisson workers. Caissons were encloseddry chambers built on riverbeds to facilitate the stru e piers. They were filledwith pressed air, and oftehe workers emerged after aended period  uhis artificial pressure they experienced mild symptoms like tingling or itchyskin. But an uable few felt more insistent pain in the joints and occasionally collapsedin agony, sometimes o get up again.

    It was all most puzzling. Sometimes workers would go to bed feeling fine, but wake upparalyzed. Sometimes they wouldn’t wake up at all. Ashcroft relates a story ing thedirectors of a unnel uhe Thames who held a celebratory ba as the tunnelneared pletion. To their sternation their champagne failed to fizz when uncorked inthe pressed air of the tunnel. However, when at length they emerged into the fresh air of aLondon evening, the bubbles sprang instantly to fizziness, memorably enlivening thedigestive process.

    Apart from avoiding high-pressure enviros altogether, only twies are reliablysuccessful against the bends. The first is to suffer only a very short exposure to the ges inpressure. That is why the free divers I mentioned earlier  desd to depths of five hundredfeet without ill effect. They don’t stay under long enough for the nitrogen in their system todissolve into their tissues. The other solution is to asd by careful stages. This allows thelittle bubbles of nitrogen to dissipate harmlessly.

    A great deal of what we know about surviving at extremes is owed to the extraordinaryfather-and-son team of John Scott and J. B. S. Haldane. Even by the demanding standards ofBritish intellectuals, the Haldanes were outstandingly etric. The senior Haldane was bornin 1860 to an aristocratic Scottish family (his brother was Vist Haldane) but spent mostof his career in parative modesty as a professor of physiology at Oxford. He wasfamously absent-minded. Oer his wife had sent him upstairs to ge for a dinnerparty he failed to return and was discovered asleep in bed in his pajamas. When roused,Haldane explaihat he had found himself disrobing and assumed it was bedtime. His ideaof a vacation was to travel to wall to study hookworm in miners. Aldous Huxley, the grandson of T. H. Huxley, who lived with the Haldanes for a time, parodied him, atouch mercilessly, as the stist Edward Tantamount in the novel Point ter Point .

    Haldane’s gift to diving was to work out the rest intervals necessary to manage an astfrom the depths without getting the bends, but his is ranged across the whole ofphysiology, from studying altitude siess in climbers to the problems of heatstroke iregions. He had a particular i in the effects of toxic gases on the human body. Touand more exactly how onoxide leaks killed miners, he methodically poisonedhimself, carefully taking and measuring his own blood samples the while. He quit only whenhe was on the verge of losing all muscle trol and his blood saturation level had reached 56pert—a level, as Trevor Norton notes in his eaining history of diving, Stars Behe Sea, only fraally removed from nearly certaihality.

    Haldane’s son Jack, known to posterity as J.B.S., was a remarkable prodigy who took a in his father’s work almost from infancy. At the age of three he was overhearddemanding peevishly of his father, “But is it oxyhaemoglobin or carboxyhaemoglobin?”

    Throughout his youth, the young Haldane helped his father with experiments. By the time hewas a teehe two ofteed gases and gas masks together, taking turns to see howlong it took them to pass out.

    Though J. B. S. Haldane ook a degree in sce (he studied classics at Oxford), hebecame a brilliant stist in his ht, mostly in Cambridge. The biologist PeterMedawar, who spent his life aroual Olympians, called him “the cleverest man I everknew.” Huxley likewise parodied the younger Haldane in his novel Antic Hay, but also usedhis ideas oiipulation of humans as the basis for the plot of Brave New World.

    Among many other achievements, Haldane played a tral role in marrying Darrinciples of evolution to the geic work or Meo produce what is known togeicists as the Modern Synthesis.

    Perhaps uniquely among human beings, the younger Haldane found World War I “a veryenjoyable experience” and freely admitted that he “ehe opportunity of killing people.”

    He was himself wouwice. After the war he became a successful popularizer of sd wrote twenty-three books (as well as over four hundred stific papers). His books arestill thhly readable and instructive, though not always easy to find. He also became ahusiastic Marxist. It has been suggested, not altogether ically, that this was out of apurely trarian instinct, and that if he had been born in the Soviet Union he would havebeen a passionate monarchist. At all events, most of his articles first appeared in theunist Daily Worker.

    Whereas his father’s principal is ed miners and poisoning, the youngerHaldane became obsessed with saving submariners and divers from the unpleasantsequences of their work. With Admiralty funding he acquired a depression chamberthat he called the “pressure pot.” This was a metal der into which three people at a timecould be sealed and subjected to tests of various types, all painful and nearly all dangerous.

    Volunteers might be required to sit ier while breathing “aberrant atmosphere” orsubjected to rapid ges of pressurization. In one experiment, Haldane simulated adangerously hasty ast to see what would happen. What happened was that the dentalfillings in his teeth exploded. “Almost every experiment,” Norton writes, “ended withsomeone having a seizure, bleeding, or vomiting.” The chamber was virtually soundproof, sothe only way for octs to signal unhappiness or distress was to tap insistently on thechamber wall or to hold up o a small window.

    On another occasion, while poisoning himself with elevated levels of oxygen, Haldane hada fit so severe that he crushed several vertebrae. Collapsed lungs were a routine hazard.

    Perforated eardrums were quite on, but, as Haldane reassuringly noted in one of hisessays, “the drum generally heals up; and if a hole remains in it, although one is somewhatdeaf, one  blow tobaoke out of the ear iion, which is a socialaplishment.”

    What was extraordinary about this was not that Haldane was willing to subject himself tosuch risk and disfort in the pursuit of sce, but that he had no trouble talkingcolleagues and loved ones into climbing into the chamber, too. Sent on a simulated dest,his wife once had a fit that lasted thirteen minutes. When at last she stopped boung acrossthe floor, she was helped to her feet a home to cook dinner. Haldane happily employedwhoever happeo be around, including on one memorable occasion a former primeminister of Spain, Juan Negrín. Dr. Negrín plained afterward of minor tingling and “acurious velvety sensation on the lips” but otherwise seems to have escaped unharmed. He mayhave sidered himself very lucky. A similar experiment with oxygen deprivatioHaldahout feeling in his buttocks and lower spine for six years.

    Among Haldane’s many specific preoccupations was nitrogen intoxication. For reasons thatare still poorly uood, beh depths of about a hundred feet nitrogen bees apowerful intoxit. Us influence divers had been known to offer their air hoses topassing fish or decide to try to have a smoke break. It also produced wild mood swings. Iest, Haldaed, the subject “alternated between depression aion, at onemoment begging to be depressed because he felt ‘bloody awful’ and the  minutelaughing and attempting to interfere with his colleague’s dexterity test.” In order to measurethe rate of deterioration in the subject, a stist had to go into the chamber with thevoluo duct simple mathematical tests. But after a few minutes, as Haldaerrecalled, “the tester was usually as intoxicated as the testee, and often fot to press thespindle of his stopwatch, or to take proper notes.” The cause of the inebriation is even now amystery. It is thought that it may be the same thing that causes alcohol intoxication, but as noone knows for certain what causes that we are he wiser. At all events, without thegreatest care, it is easy to get in trouble once you leave the surface world.

    Which brings us back (well, nearly) to our earlier observation that Earth is not the easiestplace to be an anism, even if it is the only place. Of the small portion of the pla’ssurface that is dry enough to stand on, a surprisingly large amount is too hot or cold or dry orsteep or lofty to be of much use to us. Partly, it must be ceded, this is our fault. In terms ofadaptability, humans are pretty amazingly useless. Like most animals, we don’t much likereally hot places, but because we sweat so freely and easily stroke, we are especiallyvulnerable. In the worst circumstances—on foot without water in a hot desert—most peoplewill grow delirious and keel over, possibly o rise again, in no more than six or sevenhours. We are no less helpless in the face of cold. Like all mammals, humans are good atgei but—because we are so nearly hairless—not good at keeping it. Even in quitemild weather half the calories you burn go to keep your body warm. Of course, we ter these frailties to a large extent by employing clothing and shelter, but even so theportions of Earth on which repared or able to live are modest indeed: just 12 pertof the total land area, and only 4 pert of the whole surface if you include the seas.

    Yet when you sider ditions elsewhere in the known universe, the wonder is not thatwe use so little of our pla but that we have mao find a plahat we  use even abit of. You have only to look at our own solar system—or, e to that, Earth at certainperiods in its own history—to appreciate that most places are much harsher and much lessameo life than our mild, blue watery globe.

    So far space stists have discovered about seventy plas outside the solar system, outof the ten billion trillion or so that are thought to be out there, so humans  hardly claim tospeak with authority oter, but it appears that if you wish to have a pla suitable forlife, you have to be just awfully lucky, and the more advahe life, the luckier you have tobe. Various observers have identified about two dozen particularly helpful breaks we havehad oh, but this is a flying survey so we’ll distill them down to the principal four. Theyare:

    Excellent location.We are, to an almost uny degree, the right distance from the right sortof star, ohat is big enough to radiate lots of energy, but not so big as to burn itself outswiftly. It is a curiosity of physics that the larger a star the more rapidly it burns. Had our suen times as massive, it would have exhausted itself after ten million years instead of tenbillion and we wouldn’t be here now. We are also fortuo orbit where we do. Too muearer and everything oh would have boiled away. Much farther away and everythingwould have frozen.

    In 1978, an astrophysicist named Michael Hart made some calculations and cluded thatEarth would have been uninha<q></q>bitable had it been just 1 pert farther from or 5 pertcloser to the Sun. That’s not much, and in fact it wasn’t enough. The figures have since beenrefined and made a little menerous—5 pert nearer and 15 pert farther are thoughtto be more accurate assessments for our zone of habitability—but that is still a narrow belt.

    1To appreciate just how narrow, you have only to look at Venus. Venus is only twenty-fivemillion miles closer to the Sun than we are. The Sun’s warmth reaches it just two minutesbefore it touches us. In size and position, Venus is very like Earth, but the smalldifferen orbital distance made all the differeo how it turned out. It appears thatduring the early years of the solar system Venus was only slightly warmer thah andprobably had os. But those few degrees of extra warmth meant that Venus could not holdon to its surface water, with disastrous sequences for its climate. As its water evaporated,the hydrogen atoms escaped into space, and the oxygen atoms bined with carbon to forma demosphere of the greenhouse gas CO2. Venus became stifling. Although people ofmy age will recall a time when astronomers hoped that Venus might harbor life beh itspadded clouds, possibly even a kind of tropical verdure, we now know that it is much toofier enviro for any kind of life that we  reasonably ceive of. Its surfacetemperature is a roasting 470 degrees tigrade (roughly 900 degrees Fahre), which ishot enough to melt lead, and the atmospheric pressure at the surface is imes that ofEarth, or more than any human body could withstand. We lack the teology to make suitsor even spaceships that would allow us to visit. Our knowledge of Venus’s surface is based ondistant radar imagery and some startled squawks from an unmanned Soviet probe that wasdropped hopefully into the clouds in 1972 and funed for barely an hour beforepermaly shutting down.

    So that’s what happens when you move two light minutes closer to the Sun. Travel fartherout and the problem bees not heat but cold, as Mars frigidly attests. It, too, was once amuch more genial place, but couldn’t retain a usable atmosphere and turned into a frozenwaste.

    But just being the right distance from the Sun ot be the whole story, for otherwise theMoon would be forested and fair, which patently it is not. For that you o have:

    The right kind of pla.I don’t imagine even many geophysicists, when asked to ttheir blessings, would include living on a pla with a molten interior, but it’s a pretty nearcertainty that without all that magma swirling arouh us we wouldn’t be here now.

    Apart from much else, our lively interior created the outgassing that helped to build anatmosphere and provided us with the magic field that shields us from ic radiation. Italso gave us plate teics, which tinually renews and rumples the surface. If Earth wereperfectly smooth, it would be covered everywhere with water to a depth of four kilometers.

    There might be life in that lonesome o, but there certainly wouldn’t be baseball.

    In addition to having a beneficial interior, we also have the right elements in the correctproportions. In the most literal way, we are made of the right stuff. This is so crucial to ourwell-being that we are going to discuss it more fully in a minute, but first we o siderthe two remaining factors, beginning with another ohat is often overlooked:

    1The discovery of extremophiles in the boiling mudpots of Yellowstone and similar anisms found elsewheremade stists realize that actually life of a type could range much farther than that-even, perhaps, beh theicy skin of Pluto. What we are talking about here are the ditions that would produce reasonably plexsurface creatures.

    We’re a twin pla.Not many of us normally think of the Moon as a panion pla,but that is in effect what it is. Most moons are tiny iion to their master plaheMartian satellites of Phobos and Deimos, for instance, are only about ten kilometers indiameter. Our Moon, however, is more than a quarter the diameter of the Earth, .９9ｌｉｂ.ich makesours the only pla in the solar system with a sizeable moon in parison to itself (exceptPluto, which doesn’t really t because Pluto is itself so small), and what a differehatmakes to us.

    Without the Moon’s steadying influehe Earth would wobble like a dying top, withgoodness knows what sequences for climate aher. The Moon’s steady gravitationalinfluence keeps the Earth spinning at the right speed and ao provide the sort of stabilitynecessary for the long and successful development of life. This won’t go on forever. TheMoon is slipping from rasp at a rate of about 1.5 inches a year. In awo billionyears it will have receded so far that it won’t keep us steady and we will have to e up withsome other solution, but in the meantime you should think of it as much more than just apleasaure in the night sky.

    For a long time<bdo>藏书网</bdo>, astronomers assumed that the Moon ah either formed together orthat the Earth captured the Moon as it drifted by. We now believe, as you will recall from anearlier chapter, that about 4.5 billion years ago a Mars-sized object slammed ih,blowing out enough material to create the Moon from the debris. This was obviously a verygood thing for us—but especially so as it happened such a long time ago. If it had happened in1896 or last Wednesday clearly we wouldn’t be nearly so pleased about it. Which brings us toour fourth and in many ways most crucial sideration:

    Timing.The universe is an amazingly fickle aful place, and our existehin itis a wonder. If a long and unimaginably plex sequence of events stretg back 4.6billion years or so hadn’t played out in a particular ma particular times—if, to take justone obvious instahe dinosaurs hadn’t been wiped out by a meteor when they were—youmight well be six inches long, with whiskers and a tail, and reading this in a burrow.

    We don’t really know for sure because we have nothing else to pare our oweo, but it seems evident that if you wish to end up as a moderately advahinking society,you o be at the right end of a very long  of outes involving reasonable periodsof stability interspersed with just the right amount of stress and challenge (ice ages appear tobe especially helpful in this regard) and marked by a total absence of real cataclysm. As weshall see in the pages that remain to us, we are very lucky to find ourselves in that position.

    And on that note, let us now turn briefly to the elements that made us.

    There are wo naturally  elements oh, plus a further twenty or so thathave beeed in labs, but some of these we  immediately put to one side—as, in fact,chemists themselves tend to do. Not a few of our earthly chemicals are surprisingly littleknown. Astatine, for instance, is practically unstudied. It has a name and a pla theperiodic table ( door to Marie Curie’s polonium), but almost nothing else. The problemisn’t stifidifference, but rarity. There just isn’t much astati there. The mostelusive element of all, however, appears to be francium, which is so rare that it is thought thatour entire pla may tain, at any given moment, fewer thay francium atoms.

    Altogether only about thirty of the naturally  elements are widespread oh, andbarely half a dozen are of tral importao life.

    As you might expect, oxygen is our most abundant element, ating for just under 50pert of the Earth’s crust, but after that the relative abundances are often surprising. Whowould guess, for instahat sili is the seost o oh or thattitanium is tenth? Abundance has little to do with their familiarity or utility to us. Many of themore obscure elements are actually more on thater-knowhere is morecerium oh than copper, more neodymium and lanthanum than cobalt or nitrogen. Tinbarely makes it into the top fifty, eclipsed by such relative obscurities as praseodymium,samarium, gadolinium, and dysprosium.

    Abundance also has little to do with ease of dete. Aluminum is the fourth mosto oh, ating for nearly a tenth of everything that’s underh yourfeet, but its existence wasn’t even suspected until it was discovered in the eenth turyby Humphry Davy, and for a long time after that it was treated as rare and precious. gressnearly put a shiny lining of aluminum foil atop the Washington Moo show what aclassy and prosperous nation we had bee, and the French imperial family in the sameperiod discarded the state silver dinner servid replaced it with an aluminum ohefashion was cutting edge even if the knives weren’t.

    Nor does abundanecessarily relate to importance. Carbon is only the fifteenth mosto, ating for a very modest 0.048 pert of Earth’s crust, but we wouldbe lost without it. What sets the carbon atom apart is that it is shamelessly promiscuous. It isthe party animal of the atomic world, latg on to many other atoms (including itself) andholding tight, f molecular ga lines of hearty robusthe very trick of naturenecessary to build proteins and DNA. As Paul Davies has written: “If it wasn’t for carbon, lifeas we know it would be impossible. Probably any sort of life would be impossible.” Yetcarbon is not all that plentiful even in humans, who so vitally depend on it. Of every 200atoms in your body, 126 are hydrogen, 51 are oxygen, and just 19 are carbon.

    2Other elements are critiot for creating life but for sustaining it. We need iron tomanufacture hemoglobin, and without it we would die. Cobalt is necessary for the creation ofvitamin B12. Potassium and a very little sodium are literally good for your nerves.

    Molybdenum, manganese, and vanadium help to keep your enzymes purring. Zinc—bless it—oxidizes alcohol.

    We have evolved to utilize or tolerate these things—we could hardly be here otherwise—but even then we live within narres of acceptance. Selenium is vital to all of us, buttake in just a little too mud it will be the last thing you ever do. The degree to whichanisms require or tolerate certais is a relic of their evolution. Sheep and cattlenow graze side by side, but actually have very different mineral requirements. Modern cattleneed quite a lot of copper because they evolved in parts of Europe and Africa where copperwas abundant. Sheep, oher hand, evolved in copper-poor areas of Asia Minor. As arule, and not surprisingly, our tolerance for elements is directly proportioo their2Of the remaining four, three are nitrogen and the remaining atom is divided among all the other elements.

    abundan the Earth’s crust. We have evolved to expect, and in some cases actually he tiny amounts of rare elements that accumulate in the flesh or fiber that we eat. But step upthe doses, in some cases by only a tiny amount, and we >99lｉb?</a>n soon cross a threshold. Much ofthis is only imperfectly uood. No one knows, for example, whether a tiny amount ofarsenic is necessary for our well-being or not. Some authorities say it is; some not. All that iscertain is that too much of it will kill you.

    The properties of the elements  beore curious still when they are bined.

    Oxygen and hydrogen, for instance, are two of the most bustion-friendly elements around,but put them together and they make inbustible water.

    3Odder still in bination aresodium, one of the most unstable of all elements, and chlorine, one of the most toxic. Drop asmall lump of pure sodium into ordinary water and it will explode with enough force to kill.

    Chlorine is even more notoriously hazardous. Though useful in small trations forkilling micranisms (it’s chlorine you smell in bleach), in larger volumes it is lethal.

    Chlorine was the element of choiany of the poison gases of the First World War. And,as many a sore-eyed swimmer will attest, even in exceedingly dilute form the human bodydoesn’t appreciate it. Yet put these two nasty elements together and what do you get? Sodiumchloride—on table salt.

    By and large, if a doesn’t naturally find its way into our systems—if it isn’tsoluble in water, say—we tend to be i of it. Lead poisons us because we were neverexposed to it until we began to fashion it into food vessels and pipes for plumbing. (Notially, lead’s symbol is Pb, for the Latin plumbum, the source word for our modernplumbing.) The Romans also flavored their wih lead, which may be part of the reasonthey are not the force they used to be. As we have seen elsewhere, our own performahlead (not to mention mercury, cadmium, and all the other industrial pollutants with which weroutinely dose ourselves) does not leave us a great deal of room for smirking. Whesdon’t ocaturally oh, we have evolved no tolerance for them, and so they tend to beextremely toxic to us, as with plutonium. Our tolerance for plutonium is zero: there is no levelat which it is not going to make you want to lie down.

    I have brought you a long way to make a small point: a big part of the reason that Earthseems so miraculously aodating is that we evolved to suit its ditions. What wemarvel at is not that it is suitable to life but that it is suitable to our life—and hardlysurprising, really. It may be that many of the things that make it so splendid to us—well-proportioned Sun, doting Moon, sociable ore magma than you  shake a stick at,and all the rest—seem splendid simply because they are what we were born to t on. Noone  altogether say.

    Other worlds may harbor beings thankful for their silvery lakes of mercury and driftingclouds of ammonia. They may be delighted that their pla doesn’t shake them silly with itsgrinding plates or spew messy gobs of lava over the landscape, but rather exists in aperma onic tranquility. Any visitors to Earth from afar would almost certainly, atthe very least, be bemused to find us living in an atmosphere posed of nitrogen, a gassulkily disined to react with anything, and oxygen, which is so partial to bustion thatwe must place fire stations throughout our cities to protect ourselves from its livelier effects.

    But even if our visitors were oxygehing bipeds with shopping malls and a fondness for3Oxygen itself is not bustible; it merely facilitates the bus tion of other things. This is just as well, for ifoxygen were  bustible, each time you lit a match all the air around you would bur into flame. Hydrogen gas,oher hand, is extremely  bustible, as the dirigible Hindenburg demonstrated on May 6, 193 inLakehurst, New Jersey, when its hydrogen fuel burst explosive) into flame, killing thirty-six people.

    aovies, it is uhat they would fih ideal. We couldn’t even give themlunch because all our foods tain traanganese, selenium, zind other elementalparticles at least some of which would be poisonous to them. To them Earth might not seem awondrously genial place at all.

    The physicist Richard Feynmao make a joke about a posteriori clusions, as theyare called. “You know, the most amazing thing happeo me tonight,” he would say. “Isaw a car with the lise plate ARW 357.  you imagine? Of all the millions of liseplates iate, what was the ce that I would see that particular oonight?

    Amazing!” His point, of course, was that it is easy to make any banal situatioraordinary if you treat it as fateful.

    So it is possible that the events and ditions that led to the rise of life oh are notquite as extraordinary as we like to think. Still, they were extraordinary enough, and ohingis certain: they will have to do until we find some better.

百度搜索 A Short History of Nearly Everything 天涯 或 A Short History of Nearly Everything 天涯在线书库 即可找到本书最新章节.