| A | B |
|---|
| inner core | a ball of hot, solid metals at the center of the Earth |
| outer core | a layer of hot liquid metals surrounding the inner core |
| mantle | Earth's thickest layer, it has a more rigid upper portion and a softer lower portion |
| crust | thin layer of rock that surrounds Earth |
| lithosphere | the crust and the very top of the mantle |
| asthenosphere | a layer or hot, soft rock in the upper mantle |
| tectonic plate | large and small rock slabs that make up the lithosphere |
| continental drift | the idea that the continents have moved or drifted apart |
| Pangaea | the huge supercontinent formed when all the continents were once joined together |
| mid-ocean ridge | underwater mountain ranges |
| convection current | the cirular motion caused when a hot material rises, cools, and sinks, then is heated and rises again |
| theory of plate tectonics | states that Earth's surface is made up of moving plates, which are driven by motions in the mantle and asthenosphere |
| divergent boundary | occurs where tectonic plates move apart |
| convergent boundary | occurs where tectonic plates push together |
| transform boundary | occurs where tectonic plates scrape past each other |
| rift valley | a gap formed between two diverging plates |
| magnetic reversal | when Earth's magnetic north and south poles switch places |
| hot spot | an area of volcanic activity that develops above a plume in the mantle |
| subduction | occurs when one tectonic plate sinks beneath another |
| continental-continental collision | occurs where two plates carrying continental crust push together |
| oceanic-oceanic subduction | occurs where one plate with oceanic crust sinks under another plate with oceanic crust |
| oceanic-continental subduction | occurs when ocean crust sinks under continental crust |
