| A | B |
|---|
| continental drift | a hypothesis proposed by Alfred Wegener, which states that continents have moved horizontally around the globe, over time, to reach their current locations |
| Pangaea | the name Alfred Wegener gave to the large landmass, made up of all continents, that he believed existed before it broke apart to form the present continents |
| seafloor spreading | the theory that magma from Earth's mantle rises to the surface at mid-ocean ridges and cools to form new seafloor, which new magma slowly pushes away from the ridge |
| magnetometer | a sensitive instrument that records magnetic data and is used to study Earth's magnetic field |
| plate tectonics | the theory that Earth's crust and upper mantle (lithosphere) are broken into sections, called plates, that slowly move around on the mantle |
| plate | in plate tectonics, a section of Earth's lithosphere (crust and upper mantle) that moves around on the mantle |
| lithosphere | the rigid, outermost layer of the earth, about 100km thick, composed of the crust and part of the mantle |
| asthenosphere | the plasticlike layer below the lithosphere in Earth's mantle |
| divergent boundary | in plate tectonics, the boundary between two plates that are diverging, or moving away from each other |
| convergent boundary | in plate tectonics, the boundary between two plates that are converging, or moving toward each other |
| subduction zone | in plate tectonics, the area where an ocean-floor plate collides with a continental plate, and the denser ocean plate sinks under the less dense continental plate |
| transform fault | in plate tectonics, a boundary between two plates that are sliding horizontally past one another |
| convection current | the driving force of plate tectonics in which hot, plasticlike material from the mantle rises to the lithosphere, moves horizontally, cools, and sinks back to the mantle |
