Some people think that the earth has always been the way it is, with many oceans and the seven continents, but it’s not true. In fact, the continents used to be joined together in one giant continent.
The name plate tectonics comes from the Latin phrases tectonicus, which means building. The theory of plate tectonics states that there are eight major plates and many minor plates in the earth’s lithosphere, which are constantly shifting (at about 50-100 mm per year). All the continents used to belong to one super continent now called Pangaea. Then, they drifted apart into Laurasia, which became North America and Eurasia, and Gondwana, which became the other continents. From there, they broke apart again.
The earth’s outer layers are divided into the lithosphere and the asthenosphere. The lithosphere is more rigid and cooler while the asthenosphere is opposite. The lithosphere has separate and distinct plates which are able to ride on top of the asthenosphere, which is a layer that flows easily. As the plates are able to move on top of it, they do shift. There are currently eight major plates. The African plate, the Australian plate, the Antarctic plate, the Indian plate which covers part of the Indian subcontinent and part of the Indian ocean, the Eurasian plate, the North and South American plates and the only major oceanic plate, the Pacific plate. There are also lots of minor plates.
The theory was actually built on an older theory of the continental drift. In the early 20th century, scientists observed that the opposite coasts on the Atlantic Ocean actually looked like they would have fit together in one piece but it was difficult to explain with the theories that were prevalent at the time.
In 1912, Alfred Wegener proposed his theory of continental drift where he said that the continents once formed a single land mass that ended up drifting apart, which was why some of them looked like they could fit back together. He compared them to slow-moving icebergs. In 1952, evidence was discovered that confirmed this theory. Sea-floor spreading was discovered where mid-ocean ridges are formed because of volcanic activity and then, those ridges drift away. In the 1960s, studies of the deep ocean floor progressed and the plate tectonic theory came into being in the late 60s. It revolutionized many other geographical studies as well.
The theory of tectonic plates explains so many things that previously confused scientists so much so that it’s considered one of the biggest scientific breakthroughs ever. For more information, check these sites.
- Animations: Multiple animations to show how the plates have been shifting for past 750 million years.
- The Story of Plate Tectonics: Discusses many aspects of plate tectonics.
- Earth's Floor: A map that clearly defines the plates.
- Plate Tectonics, the Cause of Earthquakes: Explains how plates are responsible for earthquakes.
- The Drift of the Continents: Describes how the contents drift apart.
- Plate Tectonics: Discusses plate tectonics and how it relates to other things.
- Plate Tectonics: The Mechanism: Explains how the shifting of plates actually occurs.
- Introduction: An introduction to plate tectonics.
- Earth Plate Tectonics: Covers all aspects of plate tectonics, including how it causes earthquakes.
- How It All Fits: Explains how the continents used to fit together; with links to more information.