Chapter 17: Plate Tectonics

Alfred Wegener

A German meteorologist and geophysicist who originated the theory of continental drift in 1912.

Magnetometer

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

Deep Sea Trench

A long, deep depression or chasm in the ocean floor, where older oceanic crust is destroyed through subduction.

Rift Valley

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

Divergent Boundary

A 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 sea floor.

Convergent Boundary

A place where two tectonic plates are moving toward each other; is associated with trenches, island arcs, and folded mountains.

Transform Boundary

A place where two tectonic plates slide horizontally past each other; is characterized by long faults and shallow earthquakes.

Slab Pull

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

Seafloor Spreading

The hypothesis that new ocean crust is formed at mid-ocean ridges and destroyed at deep-sea trenches, and occurs in a continuous cycle of magma intrusion and spreading.

John Tuzo-Wilson

A Canadian geophysicist and geologist who achieved worldwide acclaim for his contributions to the theory of plate tectonics.

Ridge Push

A 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.

Asthenosphere

A zone in the upper mantle of the earth that consists of slightly fluid rock that is able to flow in convection currents, which lies under the solid lithosphere.

Harry Hess

An American geologist who studied the sea floor and developed the theory of sea-floor spreading in 1960.

Mid-Ocean Ridge

An underwater mountain range that runs through Earth's oceans, where new oceanic crust is formed by volcanism.

Pangaea

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

Tectonic Plate

Huge pieces of Earth's crust that cover its surface and fit together at their edges.

Isochron

Imaginary line on a map that shows points of the same age; formed at the same time.

Continental Drift

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

Subduction

The process by which one tectonic plate slips beneath another tectonic plate.

Lithosphere

The rigid outer part of the earth, consisting of the crust and upper mantle.

Paleomagnetism

The 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.

Plate Tectonics

The theory that the Earth's lithosphere is divided into about 12 large plates and several small ones that float on and travel independently over the asthenosphere.

Magnetic Reversal

When Earth's magnetic field changes polarity between normal and reversed.