1/12/10 Chapter 17 Vocabulary Plate Tectonics Continental Drift (p. 444) Wegener’s hypothesis that the 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. Pangaea (p.444) Ancient landmass made up of all the continents that began to break apart about 200 million years ago. Isochron (p. 452) Line on the map that connects points of the same age. Magnetic Reversal (p. 451) Changes in the Earth’s magnetic field over geologic time, recorded in the ocean-floor rocks and continental basalt flows. Magnetometer (p. 448) Device used to map the ocean floor that detects small changes in the magnetic fields. Paleomagnetism (p. 451) 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. Seafloor Spreading (p. 453) 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. Covergent Boundary (p. 457) Place where two of Earth’s tectonic plates are moving toward each other; is associated with trenches, island arcs, and folded mountains. Divergent Boundary (p. 456) 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. Rift Valley (p. 456) Long, narrow depression that forms when continental crust begins to separate at a divergent boundary. Subduction (p. 457) Process by which one tectonic plate slips beneath another tectonic plate. Theory of Plate Tectonics (p. 455) States that the 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. Transform Boundary (p. 459) Place where two tectonic plates slide horizontally past each other, characterized by long faults and shallow earthquakes. Ridge Push (p. 461) 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. Slab Pull (p.462) 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.