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7.1. From continental drift to plate tectonics

Orogenic theories

The orogenic theories have emerged to explain the origin of orogenic or mountain ranges. They can be grouped into two types:

Fixist theories

They have been the predominant ones until the beginning of the 20th century, and they affirm that both the continents and the oceans have not changed their position since the Earth was formed. They only admit that there can be vertical movements, which is why they are also called verticalist theories. Some of these theories are:

Geosyncline theory

sedimentation basin is created in which many sediments accumulate that sink due to subsidenceDeeper rocks melt, magma rises and forms the ridge by folding up the rocks above.

Fases del geosinclinal propuestas por J. Dana

By Benjamín Núñez González (Own work) [CC BY-SA 4.0], via Wikimedia Commons

Theory of contraction or contractionism

The Earth, as it cooled and contracted, folded and the mountain ranges were formed.

Anointing theory

The mountain ranges were formed by the rise of granite magma from the mantle.

Mobilist or horizontalist theories

These theories explain the formation of mountain ranges as a consequence of the horizontal movements of the earth's crustAmong these theories, the following stand out:

Continental drift hypothesis

Although there were other mobilist theories before, the continental drift hypothesis was the most complete and important. Wegener, in 1912, claimed that the continents had been united in a macrocontinent, Pangea, which fragmented and moved horizontally on the ocean floor to its current position. He suggested that the Earth's rotation could be responsible for this movement.

Hypothesis of the expansion of the ocean floor

Hess proposed the hypothesis of the expansion of the ocean floor. With sonar technology, after World War II, very accurate maps of the ocean floor were made. Studying the remaining magnetism of the rocks, it was deduced that the oceanic crust was created in the ridges, in areas with volcanic activity, and was moving away from the ridge.

Edad de la corteza oceánica

By Muller et al., 2008, published on NOAA website [Public domain], via Wikimedia Commons


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