PRELUDE: AND JUST WHAT IS GEOLOGY?

Hypothesis

A possible explanation, involving only natural processes, that can explain a set of observations.

Geologic time scale

A scale that describes the intervals of geologic time.

Theory

A scientific idea supported by an abundance of evidence that has passed many tests and failed none

Scientific method

A sequence of steps for systematically analyzing scientific problems in a way that leads to verifiable results.

Plate

One of about 20 distinct pieces of the relatively rigid lithosphere.

Science

Science is simply the use of observation, experiment, and calculation to explain how nature operates, and scientists are people who study and try to understand natural phenomena.

Scientific Law

Scientific laws are not the same as scientific theories, as the former do not provide an explanation for a phenomenon, while the latter do.

Geologist

Scientists who study the earth.

Shatter cone

Small, cone-shaped fractures formed by the shock of a meteorite impact.

Gravity

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

Core

The dense, iron-rich center of the earth

Earth System

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

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.

Crust

The rock that makes up the outermost layer if 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.

Mantle

The thick layer of rock below the Earth's crust and above the core.