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today； the site of voorhies’s discovery is called ashfall fossil beds state park； and it has astylish new visitors’ center 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’t get a huge number of visitors to ashfall fossil beds state park—it’s slightly inthe middle of nowhere—and voorhies seemed pleased to show me around。 he took me to thespot atop a twenty…foot ravine where he had made his find。
“it was a dumb place to look for bones；” he said happily。 “but i wasn’t 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’t gone up this ravine or the rains hadn’t just washed out that skull；i’d have walked on by and this would never have been found。” he 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。 “well； if you’re looking forbones； you really need exposed rock。 that’s why most paleontology is done in hot； dry places。
it’s not that there are more bones there。 it’s just that you have some chance of spotting them。
in a setting like this”—he made a sweeping gesture across the vast and unvarying prairie—“you wouldn’t know where to begin。 there could be really magnificent stuff out there； butthere’s no surface clues to show you where to start looking。”
at first they thought the animals were buried alive； and voorhies stated as much in anational geographic article in 1981。 “the article called the site a ‘pompeii of prehistoric animals；’ ” he told me； “which was unfortunate because just afterward we realized that theanimals hadn’t 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—and they must have been breathing a lot of it because the ash was feetthick for hundreds of miles。” he picked up a chunk of grayish； claylike dirt and crumbled itinto my hand。 it was powdery but slightly gritty。 “nasty stuff to have to breathe；” he went on；“because it’s 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’t have been very agreeable at all。”
the bbc documentary had suggested that the existence of so much ash in nebraska was asurprise。 in fact； nebraska’s huge ash deposits had been known about for a long time。 foralmost a century they had been mined to make household cleaning powders like et andajax。 but curiously no one had ever thought to wonder where all the ash came from。
“i’m a little embarrassed to tell you；” voorhies said； smiling briefly； “that the first i thoughtabout it was when an editor at the national geographic asked me the source of all the ash andi had to confess that i didn’t know。 nobody knew。”
voorhies sent samples to colleagues all over the western united states asking if there wasanything about it that they recognized。 several months later a geologist named billbonnichsen from the idaho geological survey got in touch and told him that the ash matcheda volcanic deposit from a place called bruneau…jarbidge in southwest idaho。 the event thatkilled the plains animals of nebraska was a volcanic explosion on a scale previouslyunimagined—but big enough to leave an ash layer ten feet deep almost a thousand miles awayin eastern nebraska。 it turned out that under the western united states there was a hugecauldron of magma； a colossal volcanic hot spot； which erupted cataclysmically every600；000 years or so。 the last such eruption was just over 600；000 years ago。 the hot spot isstill there。 these days we call it yellowstone national park。
we know amazingly little about what happens beneath our feet。 it is fairly remarkable tothink that ford has been building cars and baseball has been playing world series for longerthan we have known that the earth has a core。 and of course the idea that the continents moveabout on the surface like lily pads has been mon wisdom for much less than a generation。
“strange as it may seem；” wrote richard feynman； “we understand the distribution of matterin the interior of the sun far better than we understand the interior of the earth。”
the distance from the surface of earth to the center is 3；959 miles； which isn’t so very far。
it has been calculated that if you sunk a well to the center and dropped a brick into it； it wouldtake only forty…five minutes for it to hit the bottom （though at that point it would beweightless since all the earth’s gravity would be above and around it rather than beneath it）。
our own attempts to penetrate toward the middle have been modest indeed。 one or two southafrican gold mines reach to a depth of two miles； but most mines on earth go no more thanabout a quarter of a mile beneath the surface。 if the planet were an apple； we wouldn’t yethave broken through the skin。 indeed； we haven’t even e close。
until slightly under a century ago； what the best…informed scientific minds knew aboutearth’s interior was not much more than what a coal miner knew—namely； that you could dig down through soil for a distance and then you’d hit rock and that was about it。 then in 1906；an irish geologist named r。 d。 oldham； while examining some seismograph readings from anearthquake in guatemala； noticed that certain shock waves had penetrated to a point deepwithin the earth and then bounced off at an angle； as if they had encountered some kind ofbarrier。 from this he deduced that the earth has a core。 three years later a croatia