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The Continental Drift Theory of Alfred Wegener
Continental Drift Theory is an interesting theory that was proposed in 1912 by a German meteorologist, Alfred Wegener. He theorized that the continents of the world— North and South America, Africa, Europe, Asia, Australia, and Antarctica—were once fused into a single super continent. He called it Pangaea (means "all earth"). According to this theory, Pangaea began to split apart around 200 million years ago until it reached its present state. And the continents continue to move.
The Basis of Alfred Wegener's Continental Drift Theory
He based his theory on fossils discovered in Africa that matched those found in Brazil. He theorized that once upon a time, Africa and Brazil belonged to the same continent. Scientists during Wegener's time were skeptical about his theory until the theory of tectonic plates was developed in 1960. The theory represented what is perhaps the greatest advance in the history of geology. Now geologists have a framework that explains the movement of continents, the occurrence of earthquakes, the existence of volcanoes, and the birth of mountains.
The Theory of Tectonic Plates
According to the theory, moving plates make up the earth's crust. They float on partly melted rock in the upper mantle. Since the continents are on top of these plates, they also move with the plates. The plates may crash head-on, pull-apart, or rub each other causing all sorts of geologic phenomena.
When two plates collide head-on, mountains and mountain ranges are formed. When two plates collide, and one drives below the other, volcanoes emerge. If the lava breaks the surface, it piles up to form volcanic islands. The island of Japan was formed this way. If the islands move sidewise grinding their edges as they pass, friction builds up. This causes tremors and earthquakes. When plates under the ocean move away from each other, the earth's crust may crack. Magma may ooze in this crack, creating volcanic islands (called sea mounts) under the sea. Finally, when a heavy oceanic plate hits a lighter continental plate, the lighter plate slides down (or become subducted) into the mantle. The plate's edge melt and magma rises to the surface through volcanic mountains.
When two continental plates ram into each other, compressing and uplifting the rock they carry, folded mountains are formed. Depending on the intensity of the collision and the types of rocks involved, the fold may range in height, from a few meters to several kilometers. The Himalayas in Asia, the Alps in Europe, and the Appalachian mountains in the United States are folded mountain ranges.
When a high-riding continental plate collides with a denser, heavier oceanic plate, the latter is pushed down into the fiery hot mantle. Its edge melts into magma or molten rock. This molten magma forces its way to the surface as volcano. The Andes Mountain range in South America and the Cascade Mountains in Washington State, Oregon, and California are volcanic ranges that were formed in this way.
Evidences of The Continental Drift Theory
Some of the evidences that are used to support the continental drift theory are the following:
1. Like a jigsaw puzzle, there is a near perfect match of the coastlines of distant continents, such as South America and Africa.
2. Found in continents separated by oceans are identical remains of fossils of certain species of plants and animals.
3. Coal deposits in Antarctica showed that this continent has experienced warm climate. That was the time when it was part of the supercontinent Pangaea.
4. Identical rock formations were found on opposite shores of the Atlantic. This is proof that these shores were once part of the continent.
5. North and South America continue to move away from Europe at the rate of 4 cm/year. India continues to move into Asia at the rate of 5 cm/year. As a consequence, Mount Everest and the Himalayan mountain ranges grow higher by 1 cm/year.
Do you know that...
fossils of coiled mollusks that are believed to have lived in the ocean around 65 million years ago were found in the Rocky Mountains of USA and the Himalayan Mountains in Nepal?