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robably be insufficient totake appropriate action。 the greater likelihood； however； is that we wouldn鈥檛 see any object鈥攅ven a et鈥攗ntil it was about six months away； which would be much too late。
shoemaker…levy 9 had been orbiting jupiter in a fairly conspicuous manner since 1929； but ittook over half a century before anyone noticed。
interestingly； because these things are so difficult to pute and must incorporate such asignificant margin of error； even if we knew an object was heading our way we wouldn鈥檛know until nearly the end鈥攖he last couple of weeks anyway鈥攚hether collision was certain。
for most of the time of the object鈥檚 approach we would exist in a kind of cone of uncertainty。
it would certainly be the most interesting few months in the history of the world。 and imaginethe party if it passed safely。
鈥渟o how often does something like the manson impact happen？鈥潯 asked anderson andwitzke before leaving。
鈥渙h； about once every million years on average；鈥潯aid witzke。
鈥渁nd remember；鈥潯dded anderson； 鈥渢his was a relatively minor event。 do you know howmany extinctions were associated with the manson impact？鈥�
鈥渘o idea；鈥潯 replied。
鈥渘one；鈥潯e said； with a strange air of satisfaction。 鈥渘ot one。鈥�
of course； witzke and anderson added hastily and more or less in unison； there wouldhave been terrible devastation across much of the earth； as just described； and pleteannihilation for hundreds of miles around ground zero。 but life is hardy； and when the smokecleared there were enough lucky survivors from every species that none permanentlyperished。
the good news； it appears； is that it takes an awful lot to extinguish a species。 the badnews is that the good news can never be counted on。 worse still； it isn鈥檛 actually necessary tolook to space for petrifying danger。 as we are about to see； earth can provide plenty of dangerof its own。
14 THE FIRE BELOW
灏忚txt澶╁爞
in the summer of 1971； a young geologist named mike voorhies was scouting around onsome grassy farmland in eastern nebraska； not far from the little town of orchard； where hehad grown up。 passing through a steep…sided gully； he spotted a curious glint in the brushabove and clambered up to have a look。 what he had seen was the perfectly preserved skull ofa young rhinoceros； which had been washed out by recent heavy rains。
a few yards beyond； it turned out； was one of the most extraordinary fossil beds everdiscovered in north america； a dried…up water hole that had served as a mass grave for scoresof animals鈥攔hinoceroses； zebra…like horses； saber…toothed deer； camels； turtles。 all had diedfrom some mysterious cataclysm just under twelve million years ago in the time known togeology as the miocene。 in those days nebraska stood on a vast； hot plain very like theserengeti of africa today。 the animals had been found buried under volcanic ash up to tenfeet deep。 the puzzle of it was that there were not； and never had been； any volcanoes innebraska。
today； the site of voorhies鈥檚 discovery is called ashfall fossil beds state park； and it has astylish new visitors鈥櫋enter and museum； with thoughtful displays on the geology of nebraskaand the history of the fossil beds。 the center incorporates a lab with a glass wall throughwhich visitors can watch paleontologists cleaning bones。 working alone in the lab on themorning i passed through was a cheerfully grizzled…looking fellow in a blue work shirt whomi recognized as mike voorhies from a bbc television documentary in which he featured。
they don鈥檛 get a huge number of visitors to ashfall fossil beds state park鈥攊t鈥檚 slightly inthe middle of nowhere鈥攁nd voorhies seemed pleased to show me around。 he took me to thespot atop a twenty…foot ravine where he had made his find。
鈥渋t was a dumb place to look for bones；鈥潯e said happily。 鈥渂ut i wasn鈥檛 looking for bones。 iwas thinking of making a geological map of eastern nebraska at the time； and really just kindof poking around。 if i hadn鈥檛 gone up this ravine or the rains hadn鈥檛 just washed out that skull；i鈥檇 have walked on by and this would never have been found。鈥潯e indicated a roofedenclosure nearby； which had bee the main excavation site。 some two hundred animalshad been found lying together in a jumble。
i asked him in what way it was a dumb place to hunt for bones。 鈥渨ell； if you鈥檙e looking forbones； you really need exposed rock。 that鈥檚 why most paleontology is done in hot； dry places。
it鈥檚 not that there are more bones there。 it鈥檚 just that you have some chance of spotting them。
in a setting like this鈥濃�攈e made a sweeping gesture across the vast and unvarying prairie鈥斺�測ou wouldn鈥檛 know where to begin。 there could be really magnificent stuff out there； butthere鈥檚 no surface clues to show you where to start looking。鈥�
at first they thought the animals were buried alive； and voorhies stated as much in anational geographic article in 1981。 鈥渢he article called the site a 鈥榩ompeii of prehistoric animals；鈥櫋♀�潯e told me； 鈥渨hich was unfortunate because just afterward we realized that theanimals hadn鈥檛 died suddenly at all。 they were all suffering from something calledhypertrophic pulmonary osteodystrophy； which is what you would get if you were breathing alot of abrasive ash鈥攁nd they must have been breathing a lot of it because the ash was feetthick for hundreds of miles。鈥潯e picked up a chunk of grayish； claylike dirt and crumbled itinto my hand。 it was powdery but slightly gritty。 鈥渘asty stuff to have to breathe；鈥潯e went on；鈥渂ecause it鈥檚 very fine but also quite sharp。 so anyway they came here to this watering hole；presumably seeking relief； and died in some misery。 the ash would have ruined everything。 itwould have buried all the grass and coated every leaf and turned the water into an undrinkablegray sludge。 it couldn鈥檛 have been very agreeable at all。鈥�
the bbc documentary had suggested that the existence of so much ash in nebraska was asurprise。 in fact； nebraska鈥檚 huge ash deposits had been known about for a long time。 foralmost a century they had been mined to make household cleaning powders li