B.10. Plate Tectonics
- Given by McKenzie and Parker and also Morgan.
- A tectonic plate (lithospheric Plate) is a massive, irregularly-shaped slab of solid rock, generally composed of both continental and oceanic lithosphere.
- Plates move horizontally over the asthenosphere as rigid units.
- The theory of plate tectonics proposes that the earth’s lithosphere is divided into seven major and some minor plates.
- These plates have been constantly moving over the globe throughout the history of the Earth.
- It is not a continent that moves as believed by Wegener. Continents are part of a plate and what moves is the plate.
- The mobile rock beneath the rigid plates is believed to be moving in a circular manner. The heated material rises to the surface, spreads and begins to cool, and then sinks back deeper to generate what scientists call a conventional cell.
- Heat within the Earth comes from two main sources – Radioactive decay and residual heat.
[Image: Magnetic Field of Earth]
[Image: Oceanic Convergence]