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Plate Tectonics

The theory of plate tectonics reveals that Earth's lithosphere is divided into tectonic plates that drift slowly atop the asthenosphere. Initially, the Earth was a single supercontinent, Pangea, surrounded by one ocean. Over time, these plates moved apart, resulting in the formation of our current seven continents through processes like continental drift and sea-floor spreading. Different boundaries—divergent, convergent, and transform—describe how plates interact, leading to geological features like mountains and faults, exemplified by the San Andreas Fault and the Ring of Fire.

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Plate Tectonics

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  1. Plate Tectonics How the Earth moves

  2. The Definition • The theory of plate tectonics states that the Earth’s lithosphere is divided into pieces called tectonic plates that move around on top of the asthensophere • Plates are either oceanic or continental

  3. These plates drift very slowly—centimeters per year • Once, the world had one giant supercontinent, called Pangeaand one giant ocean. • Then, over time, the supercontinent spread out, forming the 7 continents we know today—this process is described as continental drift

  4. Sea-floor Spreading • Magma rises from the mantle and solidifies—forming new oceanic lithosphere. • Once the magma has solidified into the rocky crust, it spreads out in either direction

  5. Divergent Boundary • This is the boundary between two plates that are spreading away from one another • Like the ones found where sea-floor spreading occurs

  6. Mid-Atlantic Ridge: A Divergent boundary

  7. Convergent Boundary • A convergent boundary is formed where two plates collide with each other • Three combinations exist: • Continental/continental • Continental/oceanic • Oceanic/oceanic

  8. The Three Collisions: Convergent Boundaries

  9. Transform Boundaries • A transform boundary can be found where two plates are sliding past each other horizontally • The most famous of which is the San Andreas Fault

  10. The San Andreas Fault—A Transform Boundary

  11. How Mountains Form

  12. Types of Mountains—Folded • Folded mountains form at convergent boundaries where plates collide • Rock squeezes against rock, pushing it upward • These form the highest mountains in the world

  13. Types of Mountains—Fault-Block • When the crust is tense, the rock can break along a series of faults, causing large rock blocks to drop down lower than other rocks

  14. Types of Mountains—Volcanic • Volcanic mountains form when oceanic crust sinks into the asthenosphere by subduction • These rock melts, forming magma • This magma, under pressure, eventually rises and erupts through volcanic mountains

  15. The Ring of Fire

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