Harold Jeffreys, a leading British geophysicist of the 1920s, calculated that if continents did ride these Earth tides, mountain ranges would collapse and Earth would stop spinning within a year. His assertion that continents plowed through oceanic rock, riding tides in the Earth like an icebreaker through sea ice, brought derision from the world ’s geophysicists (scientists who study the physical properties of Earth including movements of its crust). Theory because Wegener could not satisfactorily explain how the continents moved. He even measured Greenland ’s distance from Europe over many years to show that the two are drifting slowly apart.Īlthough Wegener ’s ideas are compelling today, scientists for decades dismissed the continental drift In Wegener ’s 1915 book, The Origin of Continents and Oceans, he cited evidence that Pangaea had existed most of the evidence came from Gondawana, the southern half of the supercontinent, and included the following: glacially gouged rocks in southern Africa, South America, and India the fit of the coastlines and undersea shelves of the continents, especially eastern South America into western Africa and eastern North America into northwestern Africa fossils in South America that match fossils in Africa and Australia mountain ranges that start in Argentina and continue into South Africa and Australia and other mountain ranges like the Appalachians that begin in North America and trend into Europe.
Two scientists, Edward Suess and Alexander Du Toit, named Pangaea, Gondwanaland, and Laurasia. Gondwana is believed to have included Antarctica, Australia, Africa, South America, and India. Laurasia later subdivided into North America, Eurasia (excluding India), and Greenland. These two pieces were separated by the Tethys Sea. The two halves of the protocontinent were the northernĬontinent Laurasia and the southern continent named Gondwanaland or Gondwana. History of Wegener ’s theoryĪt one time -estimated to be 200 to 300 million years ago -all of the continents were united in one supercontinent or protocontinent named Pangaea (or Pangea, from the Greek pan, meaning all, and gaea, meaning world) that first split into two halves. Although Wegener ’s theory accounted for much of the then existing geological evidence, Wegener ’s hypothesis was specifically unable to provide a verifiable or satisfying mechanism by which continents -with all of their bulk and drag -could move over an underlying mantle that was solid enough in composition to be able to reflect seismic S waves. Technological advances necessitated by the World War II made possible the accumulation of significant evidence regarding Wegener ’s hypothesis, eventually refining and supplanting Wegner ’s theory of continental drift with modern plate tectonic theory. Other scientists also attempted to explain orogeny (mountain building) as a result of Wegner ’s continental drift. Wegner ’s hypothesis met with wide skepticism, but found support and development in the work and writings of South African geologist Alexander Du Toit, who discovered a similarity in the fossils found on the coasts of Africa and South America, indicating that the fossils were seemingly derived from a common source. In the 1920s, German geophysicist Alfred Wegener ’s writings advanced the hypothesis of continental drift, which depicted the movement of continents through an underlying oceanic crust. Eventually multiple lines of evidence allowed modern tectonic theory to replace continental drift theory. In a historical sense, the now discarded explanations of continental drift were rooted in antiquated concepts regarding Earth ’s structure.Įxplanations of continental drift that persisted well into the twentieth century made the improbable geophysical assertion that the continents moved through and across an underlying oceanic crust much as ice floats and drifts through water. These theories describe the processes by which lithospheric plates -of which the visible continents are a part -move over the asthenosphere (the molten, ductile, upper portion of Earth ’s mantle). The relative movement of the continents is explained by modern theories of plate tectonics.
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