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dge was drawn there； too。 soon maps of prehistoricseas were almost solid with hypothesized land bridges—from north america to europe； frombrazil to africa； from southeast asia to australia； from australia to antarctica。 theseconnective tendrils had not only conveniently appeared whenever it was necessary to move aliving organism from one landmass to another； but then obligingly vanished without leaving atrace of their former existence。 none of this； of course； was supported by so much as a grainof actual evidence—nothing so wrong could be—yet it was geological orthodoxy for the nexthalf century。
even land bridges couldn’t explain some things。 one species of trilobite that was wellknown in europe was also found to have lived on newfoundland—but only on one side。 noone could persuasively explain how it had managed to cross two thousand miles of hostileocean but then failed to find its way around the corner of a 200…mile…wide island。 even moreawkwardly anomalous was another species of trilobite found in europe and the pacificnorthwest but nowhere in between； which would have required not so much a land bridge as aflyover。 yet as late as 1964 when the encyclopaedia britannica discussed the rival theories； itwas wegener’s that was held to be full of “numerous grave theoretical difficulties。”
to be sure； wegener made mistakes。 he asserted that greenland is drifting west by about amile a year； which is clearly nonsense。 （it’s more like half an inch。） above all； he could offerno convincing explanation for how the landmasses moved about。 to believe in his theory youhad to accept that massive continents somehow pushed through solid crust； like a plowthrough soil； without leaving any furrow in their wake。 nothing then known could plausiblyexplain what motored these massive movements。
it was arthur holmes； the english geologist who did so much to determine the age of theearth； who suggested a possible way。 holmes was the first scientist to understand thatradioactive warming could produce convection currents within the earth。 in theory thesecould be powerful enough to slide continents around on the surface。 in his popular andinfluential textbook principles of physical geology ； first published in 1944； holmes laid outa continental drift theory that was in its fundamentals the theory that prevails today。 it wasstill a radical proposition for the time and widely criticized； particularly in the united states；where resistance to drift lasted longer than elsewhere。 one reviewer there fretted； without anyevident sense of irony； that holmes presented his arguments so clearly and pellingly thatstudents might actually e to believe them。
elsewhere； however； the new theory drew steady if cautious support。 in 1950； a vote at theannual meeting of the british association for the advancement of science showed that abouthalf of those present now embraced the idea of continental drift。 （hapgood soon after citedthis figure as proof of how tragically misled british geologists had bee。） curiously；holmes himself sometimes wavered in his conviction。 in 1953 he confessed： “i have neversucceeded in freeing myself from a nagging prejudice against continental drift； in mygeological bones； so to speak； i feel the hypothesis is a fantastic one。”
continental drift was not entirely without support in the united states。 reginald daly ofharvard spoke for it； but he； you may recall； was the man who suggested that the moon hadbeen formed by a cosmic impact； and his ideas tended to be considered interesting； evenworthy； but a touch too exuberant for serious consideration。 and so most american academicsstuck to the belief that the continents had occupied their present positions forever and thattheir surface features could be attributed to something other than lateral motions。
interestingly； oil pany geologists had known for years that if you wanted to find oil youhad to allow for precisely the sort of surface movements that were implied by plate tectonics。
but oil geologists didn’t write academic papers； they just found oil。
there was one other major problem with earth theories that no one had resolved； or evene close to resolving。 that was the question of where all the sediments went。 every yearearth’s rivers carried massive volumes of eroded material—500 million tons of calcium； forinstance—to the seas。 if you multiplied the rate of deposition by the number of years it hadbeen going on； it produced a disturbing figure： there should be about twelve miles ofsediments on the ocean bottoms—or； put another way； the ocean bottoms should by now bewell above the ocean tops。 scientists dealt with this paradox in the handiest possible way。
they ignored it。 but eventually there came a point when they could ignore it no longer。
in the second world war； a princeton university mineralogist named harry hess was putin charge of an attack transport ship； the uss cape johnson。 aboard this vessel was a fancynew depth sounder called a fathometer； which was designed to facilitate inshore maneuvers during beach landings； but hess realized that it could equally well be used for scientificpurposes and never switched it off； even when far out at sea； even in the heat of battle。 whathe found was entirely unexpected。 if the ocean floors were ancient； as everyone assumed； theyshould be thickly blanketed with sediments； like the mud on the bottom of a river or lake。 buthess’s readings showed that the ocean floor offered anything but the gooey smoothness ofancient silts。 it was scored everywhere with canyons； trenches； and crevasses and dotted withvolcanic seamounts that he called guyots after an earlier princeton geologist named arnoldguyot。 all this was a puzzle； but hess had a war to take part in； and put such thoughts to theback of his mind。
after the war； hess returned to princeton and the preoccupations of teaching； but themysteries of the seafloor continued to occupy a space in his thoughts。 meanwhile； throughoutthe 1950s oceanographers were undertaking more and more sophisticated surveys of theocean floors。 in so doing； they found an even bigger surprise： the mightiest and mostextensive mountain range on earth was—mostly—underwater。 it traced