Introduction :
The continental drift is a theory proposed earlier this century by the physicist-meteorologist Alfred Wegener, to try to explain, for example, the similarity in the coastal route from both sides of the Atlantic.
The arguments of the continental drift :
Scientific discoveries of the second half of the nineteenth century show amazing correlations between continents:
Thus we find geological domains and identical rocks in Europe and America: the Appalachian Mountains is of the same nature as the Vosges and Massif Central for example. We also note a certain symmetry between the coal fields of America and Europe.
The concept of isostasy is adopted by all: the continents, lighter, literally float on the mantle, a deeper and denser region.
Paléontogues find in Africa, South America, Australia, Antarctica and India exactly the same fossils of reptiles and ferns! Also traces of glacial deposits (tillites) are found on most continents which demonstrates that they have faced the same cold climate in the late Paleozoic (Primary era) and covered with ice caps.
Alfred Wegener, then deduces that the continents are moving and they formed at the end of the primary era a single continent: Pangaea.
However, the hypothesis of Wegener will be violently rejected in 1922:
"If we believe Wegener's hypothesis we must forget everything we've learned in the last seventy years and return to school." Rollin Thomas Chamberlin
It wasn't until the 1960s that Wegener's theory is confirmed with the theory of plate tectonics:
The earth crust fragmented into 12 huge plates of rock floating on the asthenosphere (upper mantle plastic layer). When one of them is moved, it rotates about a point called expansion pole; when two plates move away from each other (1-15 cm per year), they cause tearing of the crust and the appearance of a rift.
By this rift, the melt rises from the center of the Earth and cools and solidifies. This new material, to get a place, should gradually push the plates; this movement causes (on tens of millions of years) the continental drift and form new ocean floor.
This expansion is not widespread since the oceanic plate, when it is in contact with the continental plate, slides under it (subduction) to disappear in the ocean trenches (8 000-11 000 meters deep). And the continental plate in contact with another continental plate gives rise to high mountains or imposing mountain as the Alps or the Himalayas.
Reminder on "Earthcaches": There is no container or logbook on the given coordinates. Just visit the site and answer the questions by e-mail.There is no need to wait for my reply, feel free to log immediately after. If the answers are incorrect, I will let you know. Happy caching!
To validate your visit:
1-. To what super-continent belonged the Nord-Pas-De-Calais 320 million years ago?
2-. Give the name of another super-continent and explain of what it was formed.
3-. Of what is responsible the slow continental drift?
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