| A | B |
|---|
| crust | the thin, outermost layer of the Earth, or the uppermost |
| mantle | the thin, outermost layer of the Earth, or the uppermost |
| core | the central, spherical part of the Earth below the mantle |
| lithosphere | the outermost, rigid layer of the Earth that consists of the |
| asthenosphere | the soft layer of the mantle on which the pieces of the |
| mesosphere | literally, the “middle sphere” - the strong, lower part of the |
| outer core | the liquid layer of the Earth’s core that lies beneath the |
| inner core | the solid, dense center of the Earth |
| tectonic plates | a piece of the lithosphere that moves around on top of the |
| continental drift | the theory that continents can drift apart from one another and have done so in the past |
| sea-floor spreading | the process by which new oceanic lithosphere is created at |
| plate tectonics | the theory that the Earth’s lithosphere is divided into tectonic plates that move around on top of the |
| convergent boundary | the boundary between two colliding tectonic plates |
| subduction zone | the region where an oceanic plate sinks down into the |
| divergent boundary | the boundary between two tectonic plates that are moving |
| transform boundary | the boundary between two tectonic plates that are sliding past each other horizontally |
