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e much of the soil around the warm pools is crusty and thin andone can easily fall through into a scalding vent below。 in any case； as they made their wayback to their dorm； they came across a stream that they had had to leap over earlier。 theybacked up a few paces； linked arms and； on the count of three； took a running jump。 in fact； itwasn鈥檛 the stream at all。 it was a boiling pool。 in the dark they had lost their bearings。 none ofthe three survived。
i thought about this the next morning as i made a brief call； on my way out of the park； at aplace called emerald pool； in the upper geyser basin。 doss hadn鈥檛 had time to take me therethe day before； but i thought i ought at least to have a look at it； for emerald pool is a historicsite。
in 1965； a husband…and…wife team of biologists named thomas and louise brock； while ona summer study trip； had done a crazy thing。 they had scooped up some of the yellowy…brown scum that rimmed the pool and examined it for life。 to their； and eventually the widerworld鈥檚； deep surprise； it was full of living microbes。 they had found the world鈥檚 firstextremophiles鈥攐rganisms that could live in water that had previously been assumed to be much too hot or acid or choked with sulfur to bear life。 emerald pool； remarkably； was allthese things； yet at least two types of living things； sulpholobus acidocaldarius andthermophilus aquaticus as they became known； found it congenial。 it had always beensupposed that nothing could survive above temperatures of 50掳c （122掳f）； but here wereorganisms basking in rank； acidic waters nearly twice that hot。
for almost twenty years； one of the brocks鈥櫋wo new bacteria； thermophilus aquaticus；remained a laboratory curiosity until a scientist in california named kary b。 mullis realizedthat heat…resistant enzymes within it could be used to create a bit of chemical wizardry knownas a polymerase chain reaction； which allows scientists to generate lots of dna from verysmall amounts鈥攁s little as a single molecule in ideal conditions。 it鈥檚 a kind of geneticphotocopying； and it became the basis for all subsequent genetic science； from academicstudies to police forensic work。 it won mullis the nobel prize in chemistry in 1993。
meanwhile； scientists were finding even hardier microbes； now known ashyperthermophiles； which demand temperatures of 80掳c （176掳f） or more。 the warmestorganism found so far； according to frances ashcroft in life at the extremes； is pyrolobusfumarii； which dwells in the walls of ocean vents where the temperature can reach 113掳c（235。4掳f）。 the upper limit for life is thought to be about 120掳c （248掳f）； though no oneactually knows。 at all events； the brocks鈥櫋indings pletely changed our perception of theliving world。 as nasa scientist jay bergstralh has put it： 鈥渨herever we go on earth鈥攅veninto what鈥檚 seemed like the most hostile possible environments for life鈥攁s long as there isliquid water and some source of chemical energy we find life。鈥�
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 me