Plate tectonics is a theory dealing with the dynamics of the Earth’s outer shell, the lithosphere. Resting on a broad synthesis of geologic and geophysical data, it dominates current thinking in the Earth sciences. According to the theory, the lithosphere is broken into seven large and many small moving plates. These plates, each about 50 miles thick, move relative to one another an average of a few inches a year. Three types of movement are recognized at the boundaries between plates: convergent, divergent and transform-fault.
At convergent boundaries, plates move toward each other and collide. Where an oceanic plate collides with a continental plate, the oceanic plate tips down and slides beneath the continental plate forming a deep ocean trench (long, narrow, deep basin.) An example of this type of movement, called subduction, occurs at the boundary between the oceanic Nazca Plate and the continental South American Plate. Where continental plates collide, they form major mountain systems such as the Himalayas.
The theory of plate tectonics, formulated during the late 1960s, is now almost universally accepted and has had a major impact on the development of the Earth sciences. Its adoption represents a true scientific revolution, analogous in its consequences to the Rutherford and Bohr atomic models in physics or the discovery of the genetic code in biology. Incorporating the much older idea of continental drift, the theory of plate tectonics has made the study of the Earth more difficult by doing away with the notion of fixed continents, but it has at the same time provided the means of reconstructing the past geography of continents and oceans. While its impact has, to a considerable degree, run its course in marine geology and shows signs of reaching the limits of usefulness in the study of mountain-building processes, its influence on the scientific understanding of the Earth’s history, of ancient oceans and climates, and of the evolution of life is only beginning to be felt.
The diagrams below show the break-up of the supercontinent Pangaea (meaning “all lands” in Greek), which figured prominently in the theory of continental drift — the forerunner to the theory of plate tectonics.
- Rock Cycle:A Fundamental Concept of Geology (rashidfaridi.wordpress.com)
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- Discovery sheds new light on wandering continents (yubanet.com)
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- How the Mariana Trench Became Earth’s Deepest Point (news.nationalgeographic.com)