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 o