Chapter 17 - Plate Tectonics

Pangaea

Ancient landmass made up of all the continents that began to break apart about 200 million years ago.

Magnetic reversal

Changes in Earth's magnetic field over geologic time, recorded in ocean-floor rocks and continental basalt flows.

Magnetometer

Device used to map the ocean floor that detects small changes in magnetic fields.

seafloor spreading

Hess's theory that new ocean crust is formed at mid-ocean ridges and destroyed at deep-sea trenches; occurs in a continuous cycle of magma intrusion and spreading.

Isochron

Line on a map that connects points of the same age.

Rift valley

Long, narrow depression that forms when continental crust begins to separate at a divergent boundary.

Divergent boundary

Place where two of Earth's tectonic plates are moving apart; is associated with volcanism, earthquakes, and high heat flow, and is found primarily on the seafloor.

Convergent boundary

Place where two of Earth's tectonic plates are moving toward each other; is associated with trenches, islands arcs, and folded mountains.

Transform boundary

Place where two tectonic plates slide horizontally past each another that is characterized by long faults and shallow earthquakes.

Subduction

Process by which one tectonic plate slips beneath another tectonic plate.

Theory of plate tectonics

States that Earth's crust and upper mantle are broken into plates, which are huge rock slabs that move in different directions and at different rates over Earth's surface.

Paleomagnetism

Study of Earth's magnetic record using data gathered from iron-bearing minerals in rocks that have recorded the orientation of Earth's magnetic field at the time of their formation.

Slab pull

Tectonic process associated with convection currents in Earth's mantle that occurs as the weight of the subducting plate pulls the trailing lithosphere into a subduction zone.

Ridge push

Tectonic process associated with convection currents in Earth's mantle that occurs when the weight of an elevated ridge pushes an oceanic plate toward a subduction zone.

Continental drift

Wegener's hypothesis that Earth's continents were joined as a single landmass, called Pangaea, that broke apart about 200 million years ago and slowly moved to their present positions.