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.
  • Geosyncline theory.
  • Theory of contraction or contractionism.
  • Anointing theory.
• Mobilist or horizontalist theories.
  • Hypothesis of continental drift.
  • Hypothesis of the expansion of the ocean floor.
  • Plate Tectonics or Global Tectonics.

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

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

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

Theory of contraction or contractionism

Mobilist or horizontalist theories

These theories explain the formation of mountain ranges as a consequence of the horizontal movements of the earth's crust. Among 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.

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

Plate Tectonics or Glogal Tectonics

The tectonics emerged from the hypothesis of continental drift and the hypothesis of the expansion of the ocean floor. This theory is the most accepted at the moment.

Videoquiz: Answer questions in the video above about tectonics.

Animation: You can see how the distribution of the Earth's continents has changed (pointing to your city) throughout Earth's history.