Unit 7 Vocabulary Evidence for Plate Tectonics & the Formation of Crustal Features Pangaea - a supercontinent that existed 225-260 million years ago. A large landmass formed by all the continents coming together. Greek origin meaning “all lands”. theory of plate tectonics - states that the Earth is made up of several rigid plates that move on the asthenosphere. continental drift - a theory stating that the Earth's continents have been joined together and have moved away from each other at different times in the Earth's history. sea floor spreading - a process in which new ocean floor is created as molten material from the earth's mantle rises in margins between plates or ridges and spreads out. convection currents – currents caused by the expansion of a liquid, solid, or gas as temperature rises. subsidence – a lowering in the elevation of land. boundary - something that points out or shows a limit or end : dividing line. plate boundary – region where 2 plates meet. convergent boundary - areas where plates move toward each other and collide. divergent boundary - areas where plates move away from each other. transform boundary - occurs when two plates grind past each other. rift - an opening made by splitting or separation. ridge - a raised or elevated part or area. trench – a deep depression of the sea floor caused by the subduction of one plate under another (convergent). fault – a break or crack in the Earth’s surface. theory – an idea that is the best explanation of many observations and helps make new predictions. subduction zone – where oceanic plates meet a continental plate and is pushed underneath (type of convergent boundary).