| A | B |
|---|
| inner core | the solid center of Earth |
| outer core | a liquid layer of Earth's core that surrounds the solid inner core |
| mantle | the thickest layer inside Earth; it lies between the outer core and the crust and is a plastic-like solid |
| crust | the outermost layer of Earth |
| continental drift | a hypothesis that continents have moved around the globe thousands of kilometers over millions of years to reach their current locations. |
| Pangaea | the name Alfred Wegener gave to the land mass that he believed existed before it split apart to form the present continents |
| sea floor spreading | the theory that magma from Earth's mantle rises to the surface at the mid-ocean ridge and cools to form new seafloor, which new magma slowly pushes away from the ridge. |
| magnetometer | an instrument that measures the strength of Earth's magnetic field. |
| plate tectonics | the theory that Earth's crust and upper mantle (lithosphere) exist in sections called plates and that these plates slowly move around on the mantle |
| plates | sections of Earth's lithosphere (crust and upper mantle) |
| lithosphere | the rigid, outermost layer of Earth, about 100 km thick and including the crust and part of the mantle. |
| asthenosphere | the plastic-like layer below the lithosphere in Earth's mantle. |
| convergent boundary | the boundary between two plates that are moving toward each other. |
| subduction zone | a boundary where an ocean plate collides with a continental plate, and the denser ocean plate slides beneath the less dense continental plate. |
| transform fault | a boundary between two plates that are sliding past one another. |
| divergent boundary | the boundary between two plates that are spreading apart. |
| convection current | a circular current in a fluid like air, water, or molten rock; caused when the fluid is unevenly heated, so that part of it rises, and then cools and sinks, causing a circular movement. |
