A Short History of Nearly Everything- 第57部分

almost　nothing　about　it　can　be　used　to　make　reliable　predictions　about　the　properties　of　otherliquids　and　vice　versa。　if　you　knew　nothing　of　water　and　based　your　assumptions　on　thebehavior　of　pounds　most　chemically　akin　to　it—hydrogen　selenide　or　hydrogen　sulphidenotably—you　would　expect　it　to　boil　at　minus　135　degrees　fahrenheit　and　to　be　a　gas　at　roomtemperature。

most　liquids　when　chilled　contract　by　about　10　percent。　water　does　too；　but　only　down　to　apoint。　once　it　is　within　whispering　distance　of　freezing；　it　begins—perversely；　beguilingly；extremely　improbably—to　expand。　by　the　time　it　is　solid；　it　is　almost　a　tenth　morevoluminous　than　it　was　before。　because　it　expands；　ice　floats　on　water—“an　utterly　bizarreproperty；”　according　to　john　gribbin。　if　it　lacked　this　splendid　waywardness；　ice　would　sink；and　lakes　and　oceans　would　freeze　from　the　bottom　up。　without　surface　ice　to　hold　heat　in；the　water’s　warmth　would　radiate　away；　leaving　it　even　chillier　and　creating　yet　more　ice。

soon　even　the　oceans　would　freeze　and　almost　certainly　stay　that　way　for　a　very　long　time；probably　forever—hardly　the　conditions　to　nurture　life。　thankfully　for　us；　water　seemsunaware　of　the　rules　of　chemistry　or　laws　of　physics。

everyone　knows　that　water’s　chemical　formula　is　h2o；　which　means　that　it　consists　of　onelargish　oxygen　atom　with　two　smaller　hydrogen　atoms　attached　to　it。　the　hydrogen　atomscling　fiercely　to　their　oxygen　host；　but　also　make　casual　bonds　with　other　water　molecules。

the　nature　of　a　water　molecule　means　that　it　engages　in　a　kind　of　dance　with　other　watermolecules；　briefly　pairing　and　then　moving　on；　like　the　ever…changing　partners　in　a　quadrille；to　use　robert　kunzig’s　nice　phrase。　a　glass　of　water　may　not　appear　terribly　lively；　but　everymolecule　in　it　is　changing　partners　billions　of　times　a　second。　that’s　why　water　moleculesstick　together　to　form　bodies　like　puddles　and　lakes；　but　not　so　tightly　that　they　can’t　be　easilyseparated　as　when；　for　instance；　you　dive　into　a　pool　of　them。　at　any　given　moment　only　15percent　of　them　are　actually　touching。

in　one　sense　the　bond　is　very　strong—it　is　why　water　molecules　can　flow　uphill　whensiphoned　and　why　water　droplets　on　a　car　hood　show　such　a　singular　determination　to　beadwith　their　partners。　it　is　also　why　water　has　surface　tension。　the　molecules　at　the　surface　areattracted　more　powerfully　to　the　like　molecules　beneath　and　beside　them　than　to　the　airmolecules　above。　this　creates　a　sort　of　membrane　strong　enough　to　support　insects　andskipping　stones。　it　is　what　gives　the　sting　to　a　belly　flop。

i　hardly　need　point　out　that　we　would　be　lost　without　it。　deprived　of　water；　the　human　bodyrapidly　falls　apart。　within　days；　the　lips　vanish　“as　if　amputated；　the　gums　blacken；　the　nosewithers　to　half　its　length；　and　the　skin　so　contracts　around　the　eyes　as　to　prevent　blinking。”

water　is　so　vital　to　us　that　it　is　easy　to　overlook　that　all　but　the　smallest　fraction　of　the　wateron　earth　is　poisonous　to　us—deadly　poisonous—because　of　the　salts　within　it。

we　need　salt　to　live；　but　only　in　very　small　amounts；　and　seawater　contains　way　more—about　seventy　times　more—salt　than　we　can　safely　metabolize。　a　typical　liter　of　seawater　willcontain　only　about　2。5　teaspoons　of　mon　salt—the　kind　we　sprinkle　on　food—but　muchlarger　amounts　of　other　elements；　pounds；　and　other　dissolved　solids；　which　arecollectively　known　as　salts。　the　proportions　of　these　salts　and　minerals　in　our　tissues　isuncannily　similar　to　seawater—we　sweat　and　cry　seawater；　as　margulis　and　sagan　have　putit—but　curiously　we　cannot　tolerate　them　as　an　input。　take　a　lot　of　salt　into　your　body　andyour　metabolism　very　quickly　goes　into　crisis。　from　every　cell；　water　molecules　rush　off　likeso　many　volunteer　firemen　to　try　to　dilute　and　carry　off　the　sudden　intake　of　salt。　this　leavesthe　cells　dangerously　short　of　the　water　they　need　to　carry　out　their　normal　functions。　theybee；　in　a　word；　dehydrated。　in　extreme　situations；　dehydration　will　lead　to　seizures；unconsciousness；　and　brain　damage。　meanwhile；　the　overworked　blood　cells　carry　the　salt　tothe　kidneys；　which　eventually　bee　overwhelmed　and　shut　down。　without　functioningkidneys　you　die。　that　is　why　we　don’t　drink　seawater。

there　are　320　million　cubic　miles　of　water　on　earth　and　that　is　all　we’re　ever　going　to　get。

the　system　is　closed：　practically　speaking；　nothing　can　be　added　or　subtracted。　the　water　youdrink　has　been　around　doing　its　job　since　the　earth　was　young。　by　3。8　billion　years　ago；　theoceans　had　（at　least　more　or　less）　achieved　their　present　volumes。

the　water　realm　is　known　as　the　hydrosphere　and　it　is　overwhelmingly　oceanic。　ninety…seven　percent　of　all　the　water　on　earth　is　in　the　seas；　the　greater　part　of　it　in　the　pacific；　whichcovers　half　the　planet　and　is　bigger　than　all　the　landmasses　put　together。　altogether　thepacific　holds　just　over　half　of　all　the　ocean　water　（51。6　percent　to　be　precise）；　the　atlantic　has23。6　percent　and　the　indian　ocean　21。2　percent；　leaving　just　3。6　percent　to　be　accounted　forby　all　the　other　seas。　the　average　depth　of　the　ocean　is　2。4　miles；　with　the　pacific　on　averageabout　a　thousand　feet　deeper　than　the　atlantic　and　indian　oceans。　altogether　60　percent　ofthe　planet’s　surface　is　ocean　more　than　a　mile　deep。　as　philip　ball　notes；　we　would　better　callour　planet　not　earth　but　water。

of　the　3　percent　of　earth’s　water　that　is　fresh；　most　exists　as　ice　sheets。　only　the　tiniestamount—0。036　percent—is　found　in　lakes；　rivers；　and　reservoirs；　and　an　even　smaller　part—just　0。001　percent—exists　in　clouds　or　as　vapor。　nearly　90　percent　of　the　planet’s　ice　is　inantarctica；　and　most　of　the　rest　is　in　greenland。　go　to　the　south　pole　and　you　will　bestanding　on　nearly　two　miles　of　ice；　at　the　north　pole　just　fifteen　feet　of　it。　antarctica　alonehas　six　million　cubic　miles　of　ice—enough　to　raise　the　oceans　by　a　height　of　two　hundred　feetif　it　all　melted。　but　if　all　the　water　in　the　atmosphere　fell　as　rain；　evenly　everywhere；　theoceans　would　deepen　by　only　an　inch。

sea　level；　incidentally；　is　an　almost　entirely　notional　concept。　seas　are　not　level　at　all。

tides；　winds；　the　coriolis　force；　and　other　effects　alter　water　levels　considerably　from　oneocean　to　another　and　within　oceans　as　well。　the　pacific　is　about　a　foot　and　a　half　higher　alongits　western　edge—a　consequence　of　the　centrifugal　force　created　by　the　earth’s　spin。　just　aswhen　you　pull　on　a　tub　of　water　the　water　tends　to　flow　toward　the　other　end；　as　if　reluctant　toe　with　you；　so　the　eastward　spin　of　earth　piles　water　up　against　the　ocean’s　westernmargins。

considering　the　age…old　importance　of　the　seas　to　us；　it　is　striking　how　long　it　took　theworld　to　take　a　scientific　interest　in　them。　until　well　into　the　nineteenth　century　most　of　whatwas　known　about　the　oceans　was　based　on　what　washed　ashore　or　came　up　in　fishing　nets；and　nearly　all　that　was　written　was　based　more　on　anecdote　and　supposition　than　on　physicalevidence。　in　the　1830s；　the　british　naturalist　edward　forbes　surveyed　ocean　beds　throughoutthe　atlantic　and　mediterranean　and　declared　that　there　was　no　life　at　all　in　the　seas　below2；000　feet。　it　seemed　a　reasonable　assumption。　there　was　no　light　at　that　depth；　so　no　plantlife；　and　the　pressures　of　water　at　such　depths　were　known　to　be　extreme。　so　it　came　assomething　of　a　surprise　when；　in　1860；　one　of　the　first　transatlantic　telegraph　cables　washauled　up　for　repairs　from　more　than　two　miles　down；　and　it　was　found　to　be　thicklyencrusted　with　corals；　clams；　and　other　living　detritus。

the　first　really　organized　investigation　of　the　seas　didn’t　e　until　1872；　when　a　jointexpedition　between　the　british　museum；　the　royal　society；　and　the　british　government　setforth　from　portsmouth　on　a　former　warship　called　hms　challenger。　for　three　and　a　halfyears　they　sailed　the　world；　sampling　waters；　netting　fish；　and　hauling　a　dredge　throughsediments。　it　was　evidently　dreary　work。　out　of　a　plement　of　240　scientists　and　crew；　onein　four　jumped　ship　and　eight　more　died　or　went　mad—“driven　to　distraction　by　the　mind…numbing　routine　of　years　of　dredging”　in　the　words　of　the　historian　samantha　weinberg。　butthey　sailed　across　almost　70；000　nautical　miles　of　sea；　collected　over　4；700　new　species　ofmarine　organisms；　gathered　enough　information　to　create　a　fifty…volume　report　（which　tooknineteen　years　to　put　together）；　and　gave　the　world　the　name　of　a　new　scientific　discipline：

oceanography。　they　also　discovered；　by　means　of　depth　measurements；　that　there　appeared　tobe　submerged　mountains　in　the　mid…atlantic；　prompting　some　excited　observers　to　speculatethat　they　had　found　the　lost　continent　of　atlantis。

because　the　institutional　world　mostly　ignored　the　seas；　it　fell　to　devoted—and　veryoccasional—amateurs　to　tell　us　what　was　down　there。　modern　deep…water　exploration　beginswith　charles　william　beebe　and　otis　barton　in　1930。　although　they　were　equal　partners；　themore　colorful　beebe　has　always　received　far　more　written　attention。　born　in　1877　into　a　well…to…do　family　in　new　york　city；　beebe　studied　zoology　at　columbia　university；　then　took　ajob　as　a　birdkeeper　at　the　new　york　zoological　society。　tiring　of　that；　he　decided　to　adoptthe　life　of　an　a