The Plate Tectonic Theory | How Continents Move
Geology is a scientific discipline that studies the Earth’s composition and process by which it changes. Geology provides insight and new discoveries regarding the formation of the Earth, including evidence for past climates, evolutionary life, and the movement of the Earth’s tectonic plates. Many theories have emerged from the study of the Earth’s crust. For instance, pioneering geologists once speculated that the continents gradually drifted across the ocean bed to their current location. This proposal became formally known as the continental drift theory. It was first drafted by Abraham Ortelius in 1596. Continental drift theory continued as the accepted theory until 1912, when Alfred Wegener devised the theory of plate tectonics.
Wegener simply expounded on continental drift theory by probing deeper into how the Earth’s tectonic plates interact with each other. In short, plate tectonic theory explains the formation of the planet’s crust through the collision of the Earth’s tectonic plates that create geological phenomena, such as volcanic activity, seismic activity, mountain-building and more. Unfortunately, he encountered harsh ridicule and rejection from the scientific community. It wasn’t until after his death that his peers started to his work seriously on the development of plate tectonic theory.
According to plate tectonic theory, the Earth’s surface layer consists of several plates that move and interact with each other. Geologists refer to the Earth’s surface layer as the lithosphere, and it has roughly 7 large and 18 small plates. Tectonic plates may lie within the continental or oceanic lithosphere. Continental plates are composed of granite, which make them lighter and buoyant than oceanic plates. Oceanic plates have a denser composition made from basalt. In essence, the continental plates float higher than those beneath in the oceanic lithosphere. The interaction of the plates can carry continents and oceans to new locations, sometimes exclusively one or the other.
The interaction of the plates cause different reactions, depending on which lithosphere the activity takes place. For instance, the buoyant nature of the continental plates allows them to collide and create mountain ranges. This differs greatly from the oceanic plates that interact to create subducted parts in Earth’s asthenosphere, a layer of molten rock. This happens when the plates in the oceanic lithosphere collide and slip past one another to create seismic and volcanic activity. When the oceanic plates collide, one slips under the other making it subducted at depths from 185 to 435 miles beneath the Earth’s surface. At these depths, the subducted parts of the plate melt into the molten mantle. As the plates continually collide to create material, the excess becomes magma. The subduction process allows the Earth to recycle its crust constantly. This means that the ocean always changes, whereas the continents tend to change slowly over time.
Unlike the scoffers of Wegener’s time, modern geophysicists and oceanographers embrace plate tectonics theory. According to Dr. Robert D. Ballard, plate tectonics transformed geology in the same vein as evolutionary theory changed biology and physics. Many pioneers followed Wegener’s footsteps after his passing in 1930. This led to new discoveries, which lent credence to the theory that many ridiculed during his lifetime. Further geological research and findings have advanced plate tectonic theory, which have allowed scientists to unravel the mysteries of the Earth’s formation. Geologists hope that the future of the field will lead to increased understanding of the celestial bodies, including the Moon and Mars.
Follow these links to learn more about plate tectonic theory:
- Plate Tectonic Theory: Plate Boundaries and Interplate Relationships
- PBS: Intro to Plate Tectonic Theory
- Plate Tectonics: The Rocky History of an Idea
- The Theory of Plate Tectonics (PDF)
- The Earth’s Floor and Plate Tectonics
- Geology.com: All About Plate Tectonics
- The Essentials of Plate Tectonic Theory
- HowStuffWorks: Plate Tectonic Theory Videos
- U.S. Geological Survey: Plate-Tectonics Theory
- Exploratorium: Plate Tectonics
- ThinkQuest: Earth: Plate Tectonic Theory
- An Overview of Plate Tectonics Theory (PDF)
- Harry Hess: One of the Discoverers of Seafloor Spreading
- Plate Tectonics Inched Slowly From Theory to Acceptance
- Leicester University: Plate Tectonics Lecturers, Research Groups, and Links
- The University of Texas Institute for Geophysics: Plate Tectonics Links
- Manchester Essex Middle School: Plate Tectonics Links
- Resources for Earth Study and Geography Instruction: Earth Science: Plate Tectonics: Plate Tectonics Links
- 9 Earthquakes, Volcanoes and Plate Tectonics Links
- Solvay Schools: Plate Tectonic Resources
- Johnson Street Global Studies: Useful Links on Plate Tectonics
- Geology: Related Links
- The University of Purdue’s Geologic TimeScale Foundation: Links to Other Earth History Websites
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Check out articles written by Jeanne Longhorne.