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Plate tectonics and the ocean floor

Review your understanding of plate tectonics and the ocean floor in this free article aligned to NGSS standards.

Key points:

  • There are two types of tectonic plates: oceanic and continental. Oceanic plates make up the ocean floor. Continental plates make up the continents.
  • Both oceanic and continental plates are topped by crust. On average, oceanic crust is denser than continental crust.
  • A trench forms when an oceanic plate collides with another plate at a convergent boundary. When this happens, the denser plate is subducted, or pushed under, the less dense plate.
  • A mid-ocean ridge forms when two oceanic plates move apart at a divergent boundary.
  • New oceanic crust is created at mid-ocean ridges. As it ages, it moves away from the ridge and becomes cooler and denser. Eventually, the crust reaches a trench and is destroyed.
A false color map of the Mid-Atlantic Ridge. The ridge is shown in light blue in the middle of the Atlantic Ocean. Image credit: NOAA on Wikimedia Commons, public domain.

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