Prelude: And Just What is Geology?

external processes

a geomorphologic process-such as downslope movement, erosion, or deposition-that is the consequence of gravity or of the interaction between the solid Earth and its fluid envelope (air and water)

internal process

a process in the Earth System, such as plate motion, mountain building, or volcanism, ultimately caused by the Earth's internal heat

geologic time scale

a scale that describes the intervals of geologic time

geologist

a scientist who specializes in studying the Earth

plates

one of about 20 distinct pieces of the relatively rigid lithosphere

gravity

the attractive force that one mass exerts on another; the magnitude depends on the size of the objects and the distance between them

Earth System

the global interconnecting web of physical and biological phenomena involving the solid Earth, the hydrosphere, and the atmosphere

asthenosphere

the layer of the mantle that lies between 100-150 km and 350 km deep; the asthenosphere is relatively soft and can flow when acted on by force

lithosphere

the relatively rigid, nonflowable, outer 100- to 150-km-thick layer of the Earth, constituting the crust and the top part of the mantle

Geologic time

the span of time since the formation of the Earth

geology

the study of the Earth, including our planet's composition, behavior, and history

theory of plate tectonics

the theory that the outer layer of the Earth (the lithosphere) consists of separate plates that move with respect to one another