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8Sci CH15
8th Science CH15 Moving Continents
Term | Definition |
---|---|
asthenosphere | putty-like layer in Earth’s crust on which plates slide around; capable of flow |
continental drift | hypothesis first proposed by Wegener that Earth’s continents were once a single super-continent called Pangea, which broke into smaller land masses about 200 million years ago and have since moved apart to form present-day continents |
convergent boundary | boundary between two lithospheric plates colliding; Earth’s most famous volcanoes occur at convergent plate boundaries |
divergent boundary | boundary between two lithospheric plates moving away from each other resulting in magma being forced upward to the continental or oceanic crust, where it erupts as lava and forms new crust; mid-ocean ridges are divergent boundaries |
hot spots | areas of Earth’s mantle that are hotter than others; as lithospheric plates move over hot spots, magma is forced up through cracks in the lithosphere, where it erupts as lava and volcanoes build up; the islands of Hawaii were formed in this manner |
lithosphere | Earth’s rocky crust and solid, uppermost part of the mantle; all the oceans and continents of Earth move slowly over the asthenosphere on lithospheric plates |
plate tectonics | geologic theory accounting for the movement of the continents, suggesting that the solid plates of the lithosphere are moved slowly by convection currently originating deep inside Earth |
sea-floor spreading | occurs when plates beneath the ocean floor pull apart and magma from Earth’s mantle is forced upward at mid-ocean ridges where it cools and forms a new seafloor |
transform fault boundary | boundary formed when two plates slide past each other in the same direction at different speeds or slide past each other in opposite directions; the San Andreas fault Is a transform fault boundary |