Plate Tectonics Theory
The theory of plate tectonics explains how Earth's lithosphere (outer shell) is divided into several large and small plates that move over the asthenosphere (a semi-fluid layer beneath the crust). This movement shapes Earth's surface, causing earthquakes, volcanic activity, and the formation of mountains and ocean basins.
Key Components of Plate Tectonics:
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Lithospheric Plates:
- Earth's crust is divided into rigid plates that float on the asthenosphere.
- Major plates include the Pacific, North American, Eurasian, African, Antarctic, Indo-Australian, and South American Plates.
- Smaller plates include the Caribbean, Nazca, and Philippine Plates.
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Plate Movement:
- Driven by convection currents in the mantle due to heat from Earth's core.
- Plates move at rates of a few centimeters per year.
Types of Plate Boundaries:
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Divergent Boundaries (Spreading Apart)
- Plates move away from each other.
- Forms mid-ocean ridges (e.g., Mid-Atlantic Ridge) and rift valleys (e.g., East African Rift).
- New crust is created as magma rises.
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Convergent Boundaries (Colliding Plates)
- Plates move toward each other, causing:
- Oceanic-Continental Convergence: Oceanic plate subducts under a continental plate, forming volcanic mountain chains (e.g., Andes Mountains).
- Oceanic-Oceanic Convergence: One oceanic plate subducts under another, forming volcanic island arcs (e.g., Japan, Philippines).
- Continental-Continental Convergence: Two continental plates collide, creating mountains (e.g., Himalayas).
- Plates move toward each other, causing:
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Transform Boundaries (Sliding Past Each Other)
- Plates move horizontally past each other.
- Causes earthquakes (e.g., San Andreas Fault in California).
Effects of Plate Tectonics:
- Earthquakes – Sudden movements at fault lines.
- Volcanic Eruptions – Occur at subduction zones and mid-ocean ridges.
- Mountain Formation – Created by converging continental plates.
- Ocean Basin Formation – Results from divergent plate movement.
- Continental Drift – Continents move over millions of years (explained by Alfred Wegener’s continental drift theory).
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