Questions and Answers
What are tectonic plates?
The lithosphere, which is the rigid outermost shell of a planet, is broken into rigid blocks called tectonic plates.
What is the theory of plate tectonics?
Plate tectonics is the theory that Earth's outer shell is divided into plates that glide over the mantle.
How many plates are there in the world?
There are approximately 12 large tectonic plates.
How do tectonic plates move in respect to each other at convergent plate boundaries?
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What is the composition of oceanic crust?
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What is the composition of continental crust?
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Give an example of an oceanic plate.
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What is Earth's crust?
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How much does the Earth's crust extend beneath the continents?
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What is the mantle?
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What is the lithosphere?
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Name a continental plate.
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What is the asthenosphere?
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What is a rift valley?
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How does a rift valley form?
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Study Notes
Tectonic Plates Overview
- Tectonic plates are rigid blocks of the Earth's lithosphere, akin to a cracked eggshell, comprised of the crust and upper mantle.
- Earth's lithosphere consists of approximately seven to eight major plates and many minor ones.
Theory of Plate Tectonics
- Plate tectonics theory explains that the outer shell of Earth is divided into plates that glide over the mantle, which is the layer above the core.
- The lithosphere is the strong outer layer, contrasting with the more fluid mantle underneath.
Number of Plates
- There are currently 12 large semirigid tectonic plates with various shapes and sizes, separated by boundaries.
- The seven major tectonic plates account for 94% of Earth's surface area.
Movement of Tectonic Plates
- Plates move relative to each other at three types of boundaries:
- Convergent boundaries: Plates collide.
- Divergent boundaries: Plates separate.
- Transform boundaries: Plates slide past one another.
Composition of Tectonic Plates
- Tectonic plates are approximately 100 km (62 miles) thick, primarily consisting of two types of crust:
- Oceanic crust (sima): Dense, made mainly of basalt and gabbro.
- Continental crust (sial): Less dense, mainly composed of granitic rocks.
Earth's Crust
- The outermost rock layer of Earth, known as the crust, is characterized by low-density, easily melted rocks.
- The crust extends 50 km (30 miles) beneath continents and only 5-10 km (3-6 miles) beneath ocean floors.
Mantle and Lithosphere
- The mantle is located beneath the crust, composed of denser rocks and exhibiting viscous fluid behavior under stress.
- Together, the uppermost mantle and crust form the lithosphere, which acts as a single rigid layer.
Examples of Tectonic Plates
- Oceanic Plate: The Pacific Plate, which extends from the East Pacific Rise to the deep-sea trenches around the Pacific basin.
- Continental Plate: The North American Plate, which includes North America and parts of the oceanic crust.
Asthenosphere
- The asthenosphere lies beneath the lithosphere and is believed to be hotter and more fluid, extending from about 100 km (60 miles) to 700 km (450 miles) deep.
Rift Valleys
- A rift valley is an elongated trough formed by the subsidence of the Earth's crust between normal faults.
- Rift valleys occur in divergence zones, where two tectonic plates are moving apart and can be found on continents and ocean floors.
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Description
Explore the fundamental concepts of tectonic plates and the theory of plate tectonics with our flashcards. Perfect for students looking to enhance their understanding of Earth's lithosphere and its dynamics. Test your knowledge on major and minor plates and their significance in geology.
