Key Ideas

Earth’s Energy Sources: All activity in Earth’s atmosphere, oceans, and surface is powered by three sources of energy.

Earth’s Interior: Studies of seismic waves (vibrations produced by earthquakes) show that Earth has a small, solid inner core surrounded by a liquid outer core. The outer core is surrounded by the dense mantle, which in turn is surrounded by the thin low-density crust.

Plate Tectonics: Earth’s crust and a small part of its upper mantle form a rigid layer called the lithosphere. The lithosphere is divided into huge plates that move about over the plastic layer called the asthenosphere in the upper mantle.

Earth’s Magnetic Field and Magnetosphere: Electric currents in the liquid outer core generate a magnetic field. This magnetic field produces a magnetosphere that surrounds Earth.

Earth’s Atmosphere: Earth’s atmosphere differs from those of the other terrestrial planets in its chemical composition, circulation pattern, and temperature profile.

The Biosphere: Human activity is changing Earth’s biosphere, on which all living organisms depend.