| A | B |
|---|
| density | the amount of matter in a given space |
| inner core | a solid sphere of metal mainly nickel and iron, at earth's center |
| outer core | a layer of molten metal, mainly nickel and iron that surrounds earths inner core |
| mantle | the layer of rock between earths outer core and crust in which most rock is hot enough to flow convectioncurrents; earths THICKEST layer |
| crust | a thin outer layer of rock above a planets mantle, including all dry land and ocean basins |
| lithosphere | the layer of earth made up of the crust and the irgid rock of the upper mantle |
| asthenosphere | the layer in earth's upper mantle and directly underthe lithosphere in which rock is soft and weak because it is close to melting |
| tectonic plates | the large moving pieces into which Earth's lithisphere is broken and which commonly carries both oceanic and continental crust |
| continental drift | the hypothesis that earths continents move on earths surface |
| pangaea | a hypothetical supercontinent that included all of the landmasses on Earth. It began breaking apart about 200 million years ago |
| mid-ocean ridge | a long line of sea-floor mountains where new ocean crust is formed by volcanic activity along a divergant boundary |
| convection | the transfer of energy from place to place by the motion of heated gas or liquid |
| convection current | a circulation pattern in which material is heated and rises in one area then cools and sinks in another area flowing in a continuous loop |
| theory of plate tectonics | a theory stating that earths lithosphere is broken into large plates that move and change in size over time |
| divergent boundary | a boundary along which two tectonic plate move apart characterized either a mid-ocean ridge or a continental rift valley |
| convergent boundary | a boundary along which two tectonic plates push together characterized either by seduction or a continental collision |
| transform boundary | a boundary along which two tectonic plates scrape past each other and crust is neither formed nor destroyed |
| rift valley | a deep valley formed as tectonic plates move apart such as along a mid ocean ridge |
| hot spot | an area where a column of hot material rises from deep within a planets mantle and heats the lithosphereabove it often causing volcanic activity at the surface |
| subduction | the process by which an oceanic tectonic plate sinks under another plate into earths mantle |
