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What are Plate Tectonics? .livescience.com
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a. Read the following article and use the space below to define and describe Plate Tectonics.
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Definition
- Plate tectonics is the scientific theory that Earth's outer shell (the lithosphere) is divided into several large and small rigid plates that move over the softer, partially flowing layer beneath (the asthenosphere). The movement and interaction of these plates cause earthquakes, volcanic activity, mountain building, and the creation and destruction of ocean basins.
What the theory says (short description)
- The lithosphere (crust + uppermost mantle) is broken into tectonic plates. These plates carry continental and/or oceanic crust and slowly move relative to one another at rates of a few centimeters per year. Heat from Earth’s interior drives convection in the mantle and, together with forces like slab pull and ridge push, moves the plates. Where plates meet (plate boundaries), their interactions produce most geologic activity on Earth.
Types of plate boundaries and what they produce
- Divergent boundaries: Plates move apart. New crust forms as magma rises and solidifies (example: Mid-Atlantic Ridge). Features: mid-ocean ridges, volcanic basalt, rift valleys.
- Convergent boundaries: Plates move toward each other.
- Oceanic-continental convergence: denser oceanic plate subducts under continental plate → volcanic mountain chains and deep ocean trenches (example: Andes).
- Oceanic-oceanic convergence: one oceanic plate subducts under another → island arcs and trenches (example: Japan).
- Continental-continental convergence: two continents collide and crumple upward → large mountain ranges (example: Himalayas).
- Transform (strike-slip) boundaries: Plates slide past each other horizontally → earthquakes along faults (example: San Andreas Fault).
Key evidence supporting plate tectonics
- Fit of continents (like South America and Africa) and matching fossils/rock layers across oceans.
- Seafloor spreading: age of ocean crust increases away from mid-ocean ridges; magnetic stripe patterns record reversals.
- Global distribution of earthquakes and volcanoes that align with plate boundaries.
- Direct GPS and satellite measurements showing plates are moving a few cm/year.
Why it matters
- Plate tectonics explains the distribution and causes of earthquakes, volcanoes, mountain ranges, and ocean trenches. It is the unifying framework for understanding Earth’s geology, past continental arrangements, and long-term climate changes related to continental positions.
Examples to remember
- Pacific “Ring of Fire”: zone of frequent earthquakes and volcanoes around the Pacific plate margins.
- Himalayas: formed by collision of the Indian and Eurasian plates.
- Mid-Atlantic Ridge: where Eurasian and North American plates are diverging.
(If you need a shorter definition for a worksheet: “Plate tectonics is the theory that Earth’s outer shell is split into moving plates whose interactions cause earthquakes, volcanoes, and mountains.”)
- Plate tectonics is the scientific theory that Earth's outer shell (the lithosphere) is divided into several large and small rigid plates that move over the softer, partially flowing layer beneath (the asthenosphere). The movement and interaction of these plates cause earthquakes, volcanic activity, mountain building, and the creation and destruction of ocean basins.
What the theory says (short description)
- The lithosphere (crust + uppermost mantle) is broken into tectonic plates. These plates carry continental and/or oceanic crust and slowly move relative to one another at rates of a few centimeters per year. Heat from Earth’s interior drives convection in the mantle and, together with forces like slab pull and ridge push, moves the plates. Where plates meet (plate boundaries), their interactions produce most geologic activity on Earth.
Types of plate boundaries and what they produce
- Divergent boundaries: Plates move apart. New crust forms as magma rises and solidifies (example: Mid-Atlantic Ridge). Features: mid-ocean ridges, volcanic basalt, rift valleys.
- Convergent boundaries: Plates move toward each other.
- Oceanic-continental convergence: denser oceanic plate subducts under continental plate → volcanic mountain chains and deep ocean trenches (example: Andes).
- Oceanic-oceanic convergence: one oceanic plate subducts under another → island arcs and trenches (example: Japan).
- Continental-continental convergence: two continents collide and crumple upward → large mountain ranges (example: Himalayas).
- Transform (strike-slip) boundaries: Plates slide past each other horizontally → earthquakes along faults (example: San Andreas Fault).
Key evidence supporting plate tectonics
- Fit of continents (like South America and Africa) and matching fossils/rock layers across oceans.
- Seafloor spreading: age of ocean crust increases away from mid-ocean ridges; magnetic stripe patterns record reversals.
- Global distribution of earthquakes and volcanoes that align with plate boundaries.
- Direct GPS and satellite measurements showing plates are moving a few cm/year.
Why it matters
- Plate tectonics explains the distribution and causes of earthquakes, volcanoes, mountain ranges, and ocean trenches. It is the unifying framework for understanding Earth’s geology, past continental arrangements, and long-term climate changes related to continental positions.
Examples to remember
- Pacific “Ring of Fire”: zone of frequent earthquakes and volcanoes around the Pacific plate margins.
- Himalayas: formed by collision of the Indian and Eurasian plates.
- Mid-Atlantic Ridge: where Eurasian and North American plates are diverging.
(If you need a shorter definition for a worksheet: “Plate tectonics is the theory that Earth’s outer shell is split into moving plates whose interactions cause earthquakes, volcanoes, and mountains.”)
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