Geology Reference
In-Depth Information
mile deeper than the adjacent peaks to the east or west—a feature we now call a rift valley.
What'smore,theridgeanditsriftvalleydidn'tfollowasmoothandcontinuouscurvefrom
north to south. Rather, the rift valley was repeatedly offset, a hundred miles or more to the
east or to the west, by sharply defined transform faults, places where the crust was broken
anddisplaced,givingtheentireridgeajaggedandbrokenappearance.Whatwasgoingon?
Suchsuggestivefindingscouldhaveeasilybeenburiedintheavalancheofbrilliantpost-
war scientific discoveries. In one sense, they were just more data. But the lead investigat-
ors on the ocean-floor project were no ordinary publicists. Bruce Heezen and Marie Tharp,
marine geophysicists at Columbia University's Lamont Geological Observatory, devised
a new, dramatic topographic map of Earth's surface. As on other topographic maps, they
represented continental elevations with colors—higher elevations grading from greens and
yellows to browns and ultimately white at the highest, snowcapped-mountain elevations.
Great mountain ranges—the Himalayas, the Andes, the Alps—stood out clearly. Heezen
and Tharp's artistic innovation was to highlight the immense subsurface mountain ranges
in exactly the same way, albeit in varying shades and hues of blue—a technique that made
the Mid-Atlantic Ridge and other deep-sea features stand out as monumental on a global
scale. And by centering their exquisite map on the Atlantic, they highlighted the identical
shapes of the coastlines and the ridge in an unmistakable way. By the 1960s, Heezen and
Tharp's map had achieved iconic status. Whatever the cause of this parallelism, the fact
that there was some genetic link was obvious to all.
(This story of Bruce Heezen—pronounced “HAY-zen”—and his widely lauded contri-
bution has special meaning to me and my career, for when I arrived at MIT in the fall of
1966,Iwassurprisedtofindthateventhemostseniorgeologyfacultymemberswerequite
respectful and eager to shake my hand. Distinguished pedigrees—even of erroneous hom-
onymous variety—are not without some advantage in science.)
The Expanding Sea
With the revelation ofthe Mid-Atlantic Ridge, andthe discovery ofsimilar subsurface vol-
canicridgesintheEastPacificandIndianoceans,scientiststackledthepossibilityoflateral
continentalmotionswithrenewedintensity.Tobesure,continentsaren'tdriftingaimlessly,
asWegener'scoinagemightsuggest,sogeologistslookedforsomehiddenforcethatcould
dramatically rearrange Earth's surface.
Discoveryfolloweddiscovery,asnewdatakeptarrivingtoconfoundtheexperts.In1956
Heezen and his Lamont boss, seismologist Maurice Ewing, documented a remarkable as-
sociation between the position of the central rift valley of the Mid-Atlantic Ridge and a
34,000-mile-long pattern ofmoderate ocean-floor earthquakes extending aroundthe globe.
