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old ideas die hard； and not everyone rushed to embrace the exciting new theory。 well intothe 1970s； one of the most popular and influential geological textbooks； the earth by thevenerable harold jeffreys； strenuously insisted that plate tectonics was a physicalimpossibility； just as it had in the first edition way back in 1924。 it was equally dismissive ofconvection and seafloor spreading。 and in basin and range； published in 1980； john mcpheenoted that even then one american geologist in eight still didn’t believe in plate tectonics。
today we know that earth’s surface is made up of eight to twelve big plates （depending onhow you define big） and twenty or so smaller ones； and they all move in different directionsand at different speeds。 some plates are large and paratively inactive； others small butenergetic。 they bear only an incidental relationship to the landmasses that sit upon them。 thenorth american plate； for instance； is much larger than the continent with which it isassociated。 it roughly traces the outline of the continent’s western coast （which is why thatarea is so seismically active； because of the bump and crush of the plate boundary）； butignores the eastern seaboard altogether and instead extends halfway across the atlantic to themid…ocean ridge。 iceland is split down the middle； which makes it tectonically half americanand half european。 new zealand； meanwhile； is part of the immense indian ocean plate eventhough it is nowhere near the indian ocean。 and so it goes for most plates。
the connections between modern landmasses and those of the past were found to beinfinitely more plex than anyone had imagined。 kazakhstan； it turns out； was onceattached to norway and new england。 one corner of staten island； but only a corner； iseuropean。 so is part of newfoundland。 pick up a pebble from a massachusetts beach； and itsnearest kin will now be in africa。 the scottish highlands and much of scandinavia aresubstantially american。 some of the shackleton range of antarctica； it is thought； may oncehave belonged to the appalachians of the eastern u。s。 rocks； in short； get around。
the constant turmoil keeps the plates from fusing into a single immobile plate。 assumingthings continue much as at present； the atlantic ocean will expand until eventually it is muchbigger than the pacific。 much of california will float off and bee a kind of madagascar ofthe pacific。 africa will push northward into europe； squeezing the mediterranean out ofexistence and thrusting up a chain of mountains of himalayan majesty running from paris tocalcutta。 australia will colonize the islands to its north and connect by some isthmianumbilicus to asia。 these are future outes； but not future events。 the events are happeningnow。 as we sit here； continents are adrift； like leaves on a pond。 thanks to global positioningsystems we can see that europe and north america are parting at about the speed a fingernailgrows—roughly two yards in a human lifetime。 if you were prepared to wait long enough；you could ride from los angeles all the way up to san francisco。 it is only the brevity oflifetimes that keeps us from appreciating the changes。 look at a globe and what you areseeing really is a snapshot of the continents as they have been for just one…tenth of 1 percentof the earth’s history。
earth is alone among the rocky planets in having tectonics； and why this should be is a bitof a mystery。 it is not simply a matter of size or density—venus is nearly a twin of earth inthese respects and yet has no tectonic activity。 it is thought—though it is really nothing morethan a thought—that tectonics is an important part of the planet’s organic well…being。 as thephysicist and writer james trefil has put it； “it would be hard to believe that the continuousmovement of tectonic plates has no effect on the development of life on earth。” he suggeststhat the challenges induced by tectonics—changes in climate； for instance—were animportant spur to the development of intelligence。 others believe the driftings of thecontinents may have produced at least some of the earth’s various extinction events。 innovember of 2002； tony dickson of cambridge university in england produced a report；published in the journal science； strongly suggesting that there may well be a relationshipbetween the history of rocks and the history of life。 what dickson established was that thechemical position of the world’s oceans has altered abruptly and vigorously throughoutthe past half billion years and that these changes often correlate with important events inbiological history—the huge outburst of tiny organisms that created the chalk cliffs ofengland’s south coast； the sudden fashion for shells among marine organisms during the cambrian period； and so on。 no one can say what causes the oceans’ chemistry to change sodramatically from time to time； but the opening and shutting of ocean ridges would be anobvious possible culprit。
at all events； plate tectonics not only explained the surface dynamics of the earth—how anancient hipparion got from france to florida； for example—but also many of its internalactions。 earthquakes； the formation of island chains； the carbon cycle； the locations ofmountains； the ing of ice ages； the origins of life itself—there was hardly a matter thatwasn’t directly influenced by this remarkable new theory。 geologists； as mcphee has noted；found themselves in the giddying position that “the whole earth suddenly made sense。”
but only up to a point。 the distribution of continents in former times is much less neatlyresolved than most people outside geophysics think。 although textbooks give confident…looking representations of ancient landmasses with names like laurasia； gondwana； rodinia；and pangaea； these are sometimes based on conclusions that don’t altogether hold up。 asgeorge gaylord simpson observes in fossils and the history of life； species of plants andanimals from the ancient world have a habit of appearing inconveniently where they shouldn’tand failing to be where they ought。
the outline of gondwana； a once…mighty continent connecting australia； africa；antarctica； and south america； was based in large part on the distributio