There are nine major tectonic plates:
- North American (brown)
- South American (purple)
- Africa lies on two tectonic plates. They are:
- Eurasian (green)
- Amurian (turquoise)
- Indo-Australian (orange + red)
- Antarctic (dark blue)
- Pacific (yellow)
- Nazca (cyan)
- Philippine (red)
- The Farallon Plate was an ancient oceanic plate that began subducting under the west coasts of the North American and South American Plates as Pangaea (see below) broke apart during the Jurassic period. Over time, the central part of the Farallon Plate was subducted (see below) under the North American and South American Plates. The remains of the Farallon Plate are the minor Juan de Fuca, Gorda, Rivera, Cocos, and Nazca Plates.
Plate BoundariesThere are three types of boundaries: Convergent boundaries, which cause earthquakes and other tremors, divergent boundaries, where plates move away from each other, and transform fault boundaries, where the plate is cut. Plates can form volcanoes, mountains, and oceanic ridges due to their movement. Subduction occurs when two plates meet, causing one to be driven under the other plate. Volcanoes are formed when parts of the subducted and melted tectonic plate melt and rise to the surface as magma. Earthquakes are formed when pressure between the plates causes one of them to jolt and rupture along a fault line.
The Pacific Ring of Fire
See also: Expanding Earth
Plate Tectonics are the key factor behind the principle of the drifting of the continents. 250 million years ago, all of the Earth's continents were joined up as a single landmass called Pangaea. Earthquakes and volcanic activity caused by Plate Tectonics broke the landmass apart into smaller continents. The continents are still moving, at around 5 mm per month. It is believed that in 250 million years, another giant supercontinent will form.
The theory was first hypothesized by French scientist Antonio Snider-Pellegrini. In 1903, an Italian scientist «revised» the theory and hypothesized the Expanding Earth theory, showing that 180 million years ago, the Earth was once half its size and expanded, breaking Pangaea (which covered the entire face of the Earth) into smaller continents. In 1912, German meteorologist Alfred Wegener revised the theory even further, scrapping the expansion of the Earth, and based it on matching coastlines and fossil trails in South America, Africa, Madagascar, India, Antarctica, and Australia. Everyone ridiculed Wegener's theory until the 1950s, when Seafloor Spreading (see above) was validated.
- ↑ The North American plate includes Russia east of Magadan, Sakhalin, and Japan north of Tokyo. However, as seen in the map, they are sometimes considered part of their own individual plate, called the Okhotsk plate.
- Skinner, B.J. & Porter, S.C.: Physical Geology, page 17, chapt. The Earth: Inside and Out, 1987, John Wiley & Sons, ISBN 0-471-05668-5