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the land around jackson hole was just a high grassy plain。 but then a forty…mile…long faultopened within the earth； and since then； about once every nine hundred years； the tetonsexperience a really big earthquake； enough to jerk them another six feet higher。 it is theserepeated jerks over eons that have raised them to their present majestic heights of seventhousand feet。
that nine hundred years is an average鈥攁nd a somewhat misleading one。 according torobert b。 smith and lee j。 siegel in windows into the earth ； a geological history of theregion； the last major teton quake was somewhere between about five and seven thousandyears ago。 the tetons； in short； are about the most overdue earthquake zone on the planet。
hydrothermal explosions are also a significant risk。 they can happen anytime； pretty muchanywhere； and without any predictability。 鈥測ou know； by design we funnel visitors intothermal basins；鈥潯oss told me after we had watched old faithful blow。 鈥渋t鈥檚 what they eto see。 did you know there are more geysers and hot springs at yellowstone than in all therest of the world bined？鈥�
鈥渋 didn鈥檛 know that。鈥�
he nodded。 鈥渢en thousand of them； and nobody knows when a new vent might open。鈥潯edrove to a place called duck lake； a body of water a couple of hundred yards across。 鈥渋t lookspletely innocuous；鈥潯e said。 鈥渋t鈥檚 just a big pond。 but this big hole didn鈥檛 used to be here。
at some time in the last fifteen thousand years this blew in a really big way。 you鈥檇 have hadseveral tens of millions of tons of earth and rock and superheated water blowing out athypersonic speeds。 you can imagine what it would be like if this happened under； say； theparking lot at old faithful or one of the visitors鈥櫋enters。鈥潯e made an unhappy face。
鈥渨ould there be any warning？鈥�
鈥減robably not。 the last significant explosion in the park was at a place called pork chopgeyser in 1989。 that left a crater about five meters across鈥攏ot huge by any means； but bigenough if you happened to be standing there at the time。 fortunately； nobody was around so nobody was hurt； but that happened without warning。 in the very ancient past there have beenexplosions that have made holes a mile across。 and nobody can tell you where or when thatmight happen again。 you just have to hope that you鈥檙e not standing there when it does。鈥�
big rockfalls are also a danger。 there was a big one at gardiner canyon in 1999； but againfortunately no one was hurt。 late in the afternoon； doss and i stopped at a place where therewas a rock overhang poised above a busy park road。 cracks were clearly visible。 鈥渋t could goat any time；鈥潯oss said thoughtfully。
鈥測ou鈥檙e kidding；鈥潯 said。 there wasn鈥檛 a moment when there weren鈥檛 two cars passingbeneath it； all filled with； in the most literal sense； happy campers。
鈥渙h； it鈥檚 not likely；鈥潯e added。 鈥渋鈥檓 just saying it could。 equally it could stay like that fordecades。 there鈥檚 just no telling。 people have to accept that there is risk in ing here。 that鈥檚all there is to it。鈥�
as we walked back to his vehicle to head back to mammoth hot springs； doss added： 鈥渂utthe thing is； most of the time bad things don鈥檛 happen。 rocks don鈥檛 fall。 earthquakes don鈥檛occur。 new vents don鈥檛 suddenly open up。 for all the instability； it鈥檚 mostly remarkably andamazingly tranquil。鈥�
鈥渓ike earth itself；鈥潯 remarked。
鈥減recisely；鈥潯e agreed。
the risks at yellowstone apply to park employees as much as to visitors。 doss got ahorrific sense of that in his first week on the job five years earlier。 late one night； three youngsummer employees engaged in an illicit activity known as 鈥渉ot…potting鈥濃�攕wimming orbasking in warm pools。 though the park； for obvious reasons； doesn鈥檛 publicize it； not all thepools in yellowstone are dangerously hot。 some are extremely agreeable to lie in； and it wasthe habit of some of the summer employees to have a dip late at night even though it wasagainst the rules to do so。 foolishly the threesome had failed to take a flashlight； which wasextremely dangerous because 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