Plate Tectonics: Major and Minor Plates

Lithosphere and Tectonic Plates

• The average thickness of the lithosphere covered by oceanic crust is approximately 50-100 km.
• Tectonic plates move over the asthenosphere due to convection currents, which cause the asthenosphere to flow.
• The movement of tectonic plates is responsible for the Earth's most dramatic geologic events.

Continental Drift Theory

• The scientist who introduced the continental drift theory is Alfred Wegener.
• There are 7 major tectonic plates in the lithosphere.

Evidence for Continental Drift

• The break-up of the large continent Pangaea about 225 million years ago into Laurasia and Gondwanaland supports the continental drift theory.
• The fit of the coastlines of continents on opposite sides of the Atlantic Ocean provides evidence for the continental drift theory.
• The fossil of the extinct mammal-like reptile Mesosaurus, found in both South America and South Africa, supports the continental drift theory.
• The existence of similar mountain ranges of the same age, structure, and rock types in South America and Africa provides evidence for the continental drift theory.

Seafloor Spreading Theory

• According to the seafloor spreading theory, magma rises to the surface and solidifies into new oceanic crust at mid-ocean ridges due to the process of convection.
• The stripes of magnetic material on the seafloor provide strong evidence for tectonic movements, as explained by Frederick John Vine and Drummond Hoyle Matthews.
• The seafloor spreading theory explains the process of plate tectonics, including the creation of new oceanic crust.

Fossil Evidence

• The fossil of the extinct herbivorous, pig-like reptile Lystrosaurus, found in Antarctica, India, and South Africa, supports the continental drift theory.

Mid-Ocean Ridges

• The process of convection, where hot and less dense material from the mantle rises to the surface on mid-ocean ridges, is responsible for the creation of new oceanic crust according to the seafloor spreading theory.

Learn about the major and minor tectonic plates that make up the Earth's lithosphere. Understand the characteristics of these plates, including their ability to carry both continental and oceanic crust.