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life； it turns out； is infinitely more clever and adaptable than anyone had ever supposed。
this is a very good thing； for as we are about to see； we live in a world that doesn鈥檛 altogetherseem to want us here。
part v life itselfthe more i examine the universeand study the details of its architecture；the more evidence i find that theuniverse in some sense must haveknown we were ing。
…freeman dyson
w w w。x iaoshu otx t。c o m
16 LONELY PLANET
灏彙�/璇淬�倀xt澶╁爞
it isn鈥檛 easy being an organism。 in the whole universe； as far as we yet know； there isonly one place； an inconspicuous outpost of the milky way called earth； that will sustain you；and even it can be pretty grudging。
from the bottom of the deepest ocean trench to the top of the highest mountain； the zonethat covers nearly the whole of known life； is only something over a dozen miles鈥攏ot muchwhen set against the roominess of the cosmos at large。
for humans it is even worse because we happen 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 oxygen breathing。 in consequence； no less than 99。5 percent of theworld鈥檚 habitable space by volume； according to one estimate； is fundamentally鈥攊n practicalterms pletely鈥攐ff…limits to us。
it isn鈥檛 simply that we can鈥檛 breathe in water； but that we couldn鈥檛 bear the pressures。
because water is about 1；300 times heavier than air； pressures rise swiftly as you descend鈥攂y the equivalent of one atmosphere for every ten meters （thirty…three feet） of depth。 on land；if you rose to the top of a five…hundred…foot eminence鈥攃ologne cathedral or the washingtonmonument； say鈥攖he change in pressure would be so slight as to be indiscernible。 at the samedepth underwater； however； your veins would collapse and your lungs would press to theapproximate dimensions of a coke can。 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 organs rudely deformed is thought exhilarating （though notpresumably as exhilarating as having them return to their former dimensions uponresurfacing）。 to reach such depths； however； divers must be dragged down； and quite briskly；by weights。 without assistance； the 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 nanosecond； 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 can hardly claim to be masters of the abyss。
other organisms do of course manage to deal with the pressures at depth； though quite howsome of them do so is a mystery。 the deepest point in the ocean is the mariana trench in 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 colonies of amphipods； a type of crustacean similar to shrimp buttransparent； which survive without any protection at all。 most oceans are of course much shallower； but even at the average ocean depth of two and a half miles the pressure isequivalent to being squashed beneath a stack of fourteen loaded cement trucks。
nearly everyone； including the authors of some popular books on oceanography； assumesthat the human body would crumple under the immense pressures of the deep ocean。 in fact；this appears not to be the case。 because we are made largely of water ourselves； and water is鈥渧irtually inpressible；鈥潯n the words of frances ashcroft of oxford university； 鈥渢he bodyremains at the same pressure as the surrounding water； and is not crushed at depth。鈥潯t is thegases inside your body； particularly in the lungs； that cause the trouble。 these do press；though at what point the pression bees fatal is not known。 until quite recently 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； according to ashcroft； that 鈥渉umans may be more like whales and dolphins than hadbeen expected。鈥�
plenty else can go wrong； however。 in the days of diving suits鈥攖he sort that wereconnected to the surface by long hoses鈥攄ivers sometimes experienced a dreadedphenomenon known as 鈥渢he squeeze。鈥潯his occurred when the surface pumps failed； leadingto a catastrophic loss of pressure in the suit。 the air would leave the suit with such violencethat the hapless diver would be； all too literally； sucked up into the helmet and hosepipe。
when hauled to the surface； 鈥渁ll that is left in the suit are his bones and some rags of flesh；鈥�
the biologist j。 b。 s。 haldane wrote in 1947； adding for the benefit of doubters； 鈥渢his hashappened。鈥�
（incidentally； the original diving helmet； designed in 1823 by an englishman namedcharles deane； was intended not for diving but for fire…fighting。 it was called a 鈥渟mokehelmet；鈥潯ut being made of metal it was hot and cumbersome and； as deane soon discovered；firefighters had no particular eagerness to 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 investment； deane tried it underwater and found it was idealfor salvage work。）the real terror of the deep； however； is the bends鈥攏ot so much because they areunpleasant； though of course they are； as because they are so much more likely。 the air webreathe is 80 percent nitrogen。 put the human body under pressure； and that nitrogen istransformed into tiny bubbles that migrate into the blood and tissues。 if the pressure ischanged too rapidly鈥攁s with a too…quick ascent by a diver鈥攖he bubbles trapped within thebody will begin to fizz in exactly the manner of a freshly opened bottle of champagne；clogging tiny blood vessels； depriving cells of oxygen； and causing pain so excruciating thatsufferers are prone to bend double in agony鈥攈ence 鈥渢he bends。鈥�
the bends have been an occupational hazard for sponge and pearl divers since timeimmemorial but didn鈥檛 attract much attention in the western world until the nineteenthcentury； and then it was among people who didn鈥檛 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 construction of bridge piers。 they were filledwith pressed air； and often when the workers emerged after an extended period ofworking under this artificial pressure they experienced mild symptoms like tingling or itchyskin。 but an unpredictable few felt more insistent pain in the joints and occasionally collapsedin agony； sometimes never to get up again。
it was all most puzzling。 sometimes workers would go to bed feeling fine； but wake upparalyzed。 sometimes they wouldn鈥檛 wake up at all。 ashcroft relates a story concerning the