WHAT IS THE THEORY OF PLATE TECTONICS?  EARTH’S LITHOSPHERE, IS COMPOSED OF CRUST AND THE UPPER MANTLE.  Two types of crust: Continental and Oceanic  THE CRUST AND UPPER MANTLE (THE LITHOSPHERE) IS BROKEN UP INTO 12 MAJOR TECTONIC PLATES AND SEVERAL SMALLER ONES. The Theory of Plate Tectonics Key Concept Summary

5.3 Theory of Plate Tectonics (cont.) Plate Boundary – where 2 plates divide Divergent Boundary – 2 plates moving apart  Rift Valley – when continental crust separates (East Africa) Convergent Boundaries – 2 plates that are moving toward each other  Subduction – when one plate is moving below the other one  3 kinds of convergent boundaries: o-o, o-c, c-c Transform Boundary – 2 plates slide horizontally past each other.

5.3 Theory of Plate Tectonics (cont.) Mid-1960’s, geologists combined information about sea-floor spreading, Earth’s plates, and plate motions into a single theory called plate tectonics. The theory of plate tectonics states that Earth’s plates are in slow, constant motion, driven by convection currents in the mantle. Earth’s plates move b/c they are the top part of the large convection currents in Earth’s mantle. During subduction, gravity pulls denser plate edges downward, into the mantle.

Mantle Convection When things heat, they become less dense and rise. The cooler stuff sinks. The rising and sinking of warmer and cooler material in the mantle causes convection currents.

5.3 Theory of Plate Tectonics (cont.) Plates move VERY slowly---from about 1-12 cm/year. Earth’s plates can carry ocean floor, continents, or continents and oceans together. The movement of Earth’s plates has greatly changed the location of Earth’s continents, landmasses, and oceans.  Including the formation of volcanoes, mountain ranges, and deep-ocean trenches. Faults – breaks in Earth’s crust where rocks have slipped past each other – form along plate boundaries.