Theories of Continental Movement and Plate Tectonics

Geological Hypotheses of Orogenesis

The Fixist Hypothesis

The Fixist Hypothesis was the first major theory regarding the Earth's surface. Proponents believed that the current distribution of continents and oceans has remained the same since the Earth's formation. By not admitting continental movements, they explained the formation of mountain ranges (orogenesis) as a result of various vertical forces and thrusts.

The Mobilist Hypotheses

Mobilists proposed that the continents have changed their position over time. This movement would have generated horizontal forces capable of compressing large masses of rocks, causing them to fold and raise mountains. The Mobilist view evolved through several key models:

• The Hypothesis of Continental Drift: Formulated in the early twentieth century by Alfred Wegener, this hypothesis provided the first substantial evidence of continental drift. New data later confirmed the Mobilist thesis.
• The Model of Ocean Floor Spreading: As knowledge of the seabed expanded, it was confirmed that the ocean floor continuously grows and moves toward trenches. This led to models of seafloor spreading, proposing lithospheric dynamics.
• The Theory of Plate Tectonics: The acceptance of mobility and the subsequent discovery of lithospheric plates led to the issuance of this theory, which is currently accepted and in force.

Evidence Supporting the Mobility Hypothesis

Several lines of evidence support the theory that continents move and have been joined in the past:

Geological Evidence (Continental Fit)

Wegener noted that the coastlines of South America and Africa fit together like pieces of a puzzle. He also checked the continuity of certain mountain ranges and rock formations in places currently separated by oceans. These observations strongly support the idea that the continents were once united in a different configuration.

Paleoclimatic Evidence

Approximately 300 million years ago, the Earth experienced an ice age. It is known that the southern polar ice cap expanded, leaving grooves (striations) in the rocks of the continents it covered. Currently, these streaks remain on widely separated continents. The only viable explanation for this distribution is that these landmasses were united at the time of glaciation.

Paleontological Evidence (Fossil Distribution)

The Mesosaurus was a fluvial reptile that lived during the Mesozoic Era. Its fossils have been found in widely separated places, specifically South America and Africa. Wegener concluded that this river reptile could not have moved across the vast ocean from one continent to the other, thus proving that the continents must have been joined.

Paleomagnetic Evidence

By analyzing the paleomagnetism recorded in rock samples from the same continent but from different epochs, scientists can determine a point indicating the position of the magnetic poles relative to that continent at every age. By joining these points, apparent polar migration curves are generated. If two continents have moved relative to each other, their respective curves will not coincide, providing measurable proof of continental movement.