Pangea breaking up and Continental Drift
Looking at on a map of the world the profiles of the West coast of Eastern Africa and South America, we can see that there exists a perfect match between them. This finding, supported by a series of proofs, allowed the German meteorologist A. Wegener
(1880-1930) to formulate, in 1915, the theory of Continental Drift
: according to this theory, about 240 million years ago, all of the lands would have been together in one big block, a supercontinent named Pangaea
(from Ancient Greek pan
(πᾶν) meaning "entire", and Gaia
(Γαῖα) meaning "Mother Earth"), surrounded by a single ocean called Panthalassa
(from the greek "pán", all, and "thálassa", sea).
Later, about 180 million years ago, Pangaea would be divided into two major parts: to North, Laurasia
, consisting of the current portions of North America, Greenland, Europe and Asia; to South, Gondwana
, formed by current portions of South America, Africa, India, Australia and Antarctica. These two big blocks, separated by an ocean called Tethys
(from Thetis, name of the Greek deity of the sea), they would subsequently divided and gradually turned away from each other, "drifting" and giving rise to the present continents.Wegener
thought that the continents, formed of relatively low density material (on average similar to granite, and called Sial
), floated like rafts on the wrapper of underlying fluid denser material (similar to basalt and called Sima
In addition to the aforementioned correspondence between the coasts of the continents, the theory formulated by Wegener was also supported by geological, paleoclimatic and paleontological evidence.
There is a continuity between the rocks that are found along the coast of South American and African continents, currently separated by the Atlantic Ocean, and this it would testify a common origin, to which it would have followed their separation.
The analysis of sedimentary rocks, found in some areas of the planet, indicates that they originate in areas with climates different than those typical of latitudes in which they now find themselves. This apparent contradiction can be explained by admitting that the continents have not always been at the current-latitudes, but that they moved.
There are significant similarities between the fossils of terrestrial organisms found on the two coasts of the Atlantic Ocean. At first, it was assumed the existence of "continental bridges," ie thin strips of land that crossed the ocean and that would have allowed the organisms to move, but this possibility was later ruled out and the presence of these fossils was explained assuming that, in some periods of Earth's history, continents, today apart from each other, were joined and populated by organisms of the same species.
The "revolutionary" theory of continental drift was strongly opposed by the contemporary geologists of Wegener's, because they were not clarified the causes of the movements and, on the other hand, they were not known forces powerful enough to cause the movement of the continents. According to Wegener, the continents would have drifted like icebergs that move on the sea, under the influence of gravitational and differentials forces, related to the shape of Earth, or of bulges on the Earth's surface that would cause movement of the crust for restoring the balance (these assumptions, however, were not shown).
The theory of continental drift fell into oblivion until the '60s, when it was again taken into account as a consequence of significant discoveries that were accumulating thanks to exploration of the ocean floors.References for deepening
• USGS Overview: http://pubs.usgs.gov/gip/dynamic/historical.html
from Paleomap Project
• Institute for Geophysics: http://www.ig.utexas.edu/research/projects/plates/index.htm#movies
• Pangea Ultima: http://en.wikipedia.org/wiki/Pangaea_Ultima
• CONTINENTS IN COLLISION- PANGEA ULTIMA: HTTP://SCIENCE1.NASA.GOV/SCIENCE-NEWS/SCIENCE-AT-NASA/2000/AST06OCT_1/Gif source
: http://ettehiyatu.tumblr.com/post/44544320011#geology #continental_drifts #wegener #science #sciencesunday