Mechanics of Dynamic Earth and Continental Drift Theory

Dynamic Earth

The Earth's Crust

The Earth's crust is a layer of solid minerals covering the surface of the planet. There are two main types:

• The continental crust has an average thickness of 35-40 km. Its mineral composition is varied, with an outer layer of granitic character and deeper layers of basaltic character. Geologically, continents do not end at the sea but extend for hundreds of kilometers under the oceans in the so-called continental shelf.
• The oceanic crust has a much smaller thickness and a homogeneous basaltic composition. The rocks that compose it are younger and have a higher density than the continental crust. The oceanic crust covers approximately 60% of the Earth's surface.

Early Theories and Geological Enigmas

Initially, the majority of scientists believed in the cooling-contraction theory of the planet. According to this theory, as the Earth cools, it contracts, and this contraction causes the surface to crack and crease.

Several enigmas challenged this view:

• Biological-Paleontological Enigmas: The distribution of animals from South America to Africa. Ratites (South America), ostriches (Africa), and cassowaries (Australia) are related.
• Geographical Enigmas: In the 1970s, advances in the knowledge of the seabed allowed scientists to test the fit of South America into Africa, obtaining a high degree of fit.
• Geological Enigmas: Norwegian mountain ranges fit those on the east coast of Canada in both antiquity and mineralogy. Geology can also provide information on past climates.

The Continental Drift Hypothesis

In 1915, Alfred Wegener presented the hypothesis of continental drift. According to him, all continents were part of a large landmass in the past, a supercontinent named Pangaea. About 200 million years ago, this supercontinent began to split into the current continents.

The main criticism of the continental drift hypothesis was that there was no known force capable of moving and deploying a continent thousands of miles. Wegener defended his hypothesis until his death. Over time, new discoveries provided evidence that allowed scientists to resume his hypothesis and make it the most widely accepted theory today.

Evidence Supporting Continental Drift

Paleomagnetic Tests: Early investigators of paleomagnetism, which was locked in different layers of lava from ancient times in various parts of the world, met with surprises. They found that layers of basaltic lava embedded in European and Siberian coal deposits placed these locations close to the Equator. Scientists concluded that the landmasses containing the basalt layers had moved. This provided further proof supporting continental drift.

Oceanographic Evidence: The discovery of the ocean ridge system, which divides the great oceans from end to end, revealed high volcanic activity and the existence of a central depression called a rift valley, surrounded by submerged mountain chains.