Plate Tectonics: The Rocky history of one Idea

Close check of a globe often results in theobservation that many of the continent seem come fit together likea puzzle: the west African coast seems to snuggle nicely intothe east coastline of south America and the Caribbean sea; and asimilar to the right appears across the Pacific. The right is evenmore striking once the submerged continental shelves are compared ratherthan the coastlines.

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In 1912 AlfredWegener (1880-1930) noticed the very same thing and proposed thatthe continents were once compressed into a single protocontinentwhich he referred to as Pangaea (meaning "all lands"), and overtime they have actually drifted apart right into their current distribution. Hebelieved the Pangaea was intact until the late Carboniferousperiod, about 300 million year ago, when it began to break upand drift apart. However, Wegener"s hypothesis lacked a geologicalmechanism to define how the continents can drift across theearths surface as the proposed.Searching for proof to further construct his concept ofcontinental drift, Wegener came across a paleontological papersuggesting the a floor bridge had once associated Africa withBrazil. This propose land leg was an effort to define thewell well-known paleontological observation that the same fossilizedplants and also animals native the very same time duration were discovered in southern America and also Africa.The exact same was true for fossils discovered in Europe and also North America,and Madagascar and also India. Numerous of this organisms can nothave traveled across the huge oceans that at this time exist.Wegener"s drift theory appeared moreplausible than land bridges connecting every one of thecontinents. Yet that in itself to be not enough to support his idea.Another observation favoring continental drift to be the visibility of evidence for continental glaciation in the Pensylvanian period.Striae left by the scraping the glaciers end the land surface suggested thatAfrica and South America had actually been close together at the time of thisancient ice age.The very same scraping patterns can be found alongthe coastlines of south America and also South Africa.

Wegener"s drift theory also listed an alternative explanationfor the development of mountains (orogenesis). The concept beingdiscussed throughout his time was the "Contraction theory"which said that the planet was when a molten ball and in theprocess of cooling the surface cracked and also folded up onitself. The big problem with this idea was that allmountain ranges should be roughly the exact same age, and also thiswas known not to be true. Wegener"s explanation was the asthe continents moved, the top edge that the continent wouldencounter resistance and also thus compress and also fold upwards formingmountains near the leading edges of the driftingcontinents. The Sierra Nevada hills on the Pacific shore of NorthAmerica and the Andes ~ above the shore of south America werecited. Wegener also suggested that India drifted northwardinto the oriental continent thus developing the Himalayas.

Wegener ultimately proposed a mechanism for continental driftthat focused on his assertion the the rotation of the earthcreated a centrifugal force towards the equator. Hebelieved that Pangaea originated near the southern pole and also that thecentrifugal pressure of the planet led to the protocontinent tobreak apart and the result continents to drift in the direction of theequator. He called this the "pole-fleeingforce". This idea was quickly rejected by thescientific neighborhood primarily because the yes, really forcesgenerated by the rotation the the planet were calculated to beinsufficient to relocate continents. Wegener likewise tried toexplain the westward drift that the ameri by invoking thegravitational pressures of the sun and the moon, this idea to be alsoquickly rejected. Wegener"s i can not qualify to provide anadequate explanation that the forces responsible for continentaldrift and the prevailing belief that the earth was hard andimmovable brought about the scientific dismissal that his theories.

In 1929, around the time Wegener"s ideas began to be dismissed,Arthur Holmes elaborated on among Wegener"s many hypotheses; theidea the the mantle undergoes heat convection. Thisidea is based upon the truth that together a substance is heated its densitydecreases and also rises come the surface ar until that is cooled and also sinksagain. This recurring heating and also cooling results in a currentwhich may be sufficient to reason continents come move. ArthurHolmes said that this thermal convection was favor a conveyorbelt and that the upwelling pressure could break apart acontinent and also then force the damaged continent in oppositedirections carried by the convection currents. This ideareceived very little attention at the time.

Not till the 1960"s walk Holmes" idea get anyattention.Greater expertise of the s floor and the discoveries offeatures favor mid-oceanic ridges,geomagnetic anomalies parallel to the mid-oceanic ridges,and the association of island arcs and oceanic trenches occurringtogether and near the continental margins, said convectionmight indeed be in ~ work. Thesediscoveries and more led take care of Hess (1962) and R.Deitz (1961) topublish comparable hypotheses based on mantle convection currents,now recognized as "sea floor spreading". This idea wasbasically the same as that proposed by Holmes over 30 yearsearlier, but now there was much an ext evidence to more developand assistance the idea. To learn much more about the existing theorieswhich explain the instrument behind continental drift walk to the "PlateTectonics: The Mechanism" page.

To learn an ext about plate tectonics, review the publications I used as referenceslisted below:The new View that the earth by Seiya Uyeda, 1978 through W.H. Freeman and also Co.The Earth"s Dynamic systems by W. Kenneth Hamblin, 1975 by burgess Publishing Co. Worldwide Tectonics by Philip Kearey & Frederick J. Vine, 1996 by Blackwell scientific researches Ltd.Physical Geology through Carla W. Montgomery, 1987 through Wm.


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