Glossary Starting with the letter: G


See greenhouse gases


The study of the distribution and amounts of chemical elements in the various systems that comprise the Earth.


The study of processes, such as the movement of material, in the Earth’s interior.

Geologic Time

The period of time covering the physical formation and development of Earth, as recorded within the succession of rocks.


The study of Earth, its history, its composition, its structure, and the dynamic processes that shape it.


The study of the magnetic activity of Earth and its atmosphere.


The study of landforms and their origin on the surface of Earth and other planets.


The study of physical properties of Earth.


A billion pascals; a pascal is a unit of pressure (force per unit area).

Glacial period

See ice age.


The formation, advance, and retreat of glaciers through time. Glaciation of a region refers to the accumulation of ice over that region.


A large mass of ice, air, water, and rock debris formed at least partially on land which flows by internal deformation in response to gravity. Glaciers include small valley glaciers, ice streams, ice caps, and ice sheets.


An intrusive igneous rock, usually light-colored. Granites commonly contain high amounts of quartz and feldspar. Micas, such as muscovite and biotite, may also be present. The extrusive igneous counterpart to a granite is a rhyolite.

Greenhouse Gas

Gases, primarily water vapor, carbon dioxide, and methane, that increase global temperatures by absorbing outgoing radiation emitted by the Earth’s surface. Also called GHGs.


A submerged, flat-topped volcanic mountain formed in deep oceans.


The large, roughly circular current that is the main feature of wind-driven surface circulation found in most major ocean basins.