E

earthquake
Ground shaking caused by the release of energy stored in rocks.
echo sounder
A device that uses sound waves to measure the depth of the seafloor.
ecosystem
All of the living things in a region and the physical and chemical factors that they need.
effusive eruption
A relatively gentle, non-explosive volcanic eruption.
El Niño
A natural climate variation in which the trade winds weaken or reverse directions, and warm water accumulates on the ocean surface off of South America.
elastic deformation
Strain that alters the shape of a rock but that is not permanent.
elastic rebound theory
How earthquakes are generated. Stresses cause strain to build up in rocks until they can no longer bend elastically and they break, causing an earthquake.
electromagnetic (EM) radiation
Energy transmitted through space as a wave.
electromagnetic spectrum
The full range of electromagnetic radiation.
electromagnetic waves
Waves with both electrical and magnetic properties; travel by radiation.
electron
Tiny negatively charged particles that orbit the nucleus.
element
A pure chemical substance with one type of atom.
elevation
Height of a feature measured relative to sea level.
ellipse
A shape that looks like a slightly squashed circle.
elliptical galaxy
An oval or egg shaped galaxy with older stars and little gas and dust.
end moraine
Unsorted pile of glacial till that marks points where the glacier was stationary.
energy
The ability to do work or change matter.
energy efficiency
The amount of useful work that is done by a unit of energy.
epicenter
The point on the Earth’s surface directly above the focus of the earthquake.
erosion
The transport of weathered materials and sediments by water, wind, ice, or gravity.
eruption
The release of lava, tephra, and gases from a volcano.
estuary
Where a stream meets a lake or, more usually, an ocean. The mixture of fresh and salt water attracts a large number of species and so estuaries have high biodiversity.
eukaryote
A cell with a separate nucleus to hold its DNA and RNA.
evaporation
The change in a substance from a liquid to a gas by the addition of energy.
evolution
Change through time. The change in the genetic makeup of a population of organisms over time such that a new species is often the result.
exosphere
The outermost layer of the atmosphere; the gas molecules are extremely far apart.
explosive eruption
A potentially devastating eruption of rock, lava, ash, and gas exploding from a volcano.
export
To send a resource or product to another country.
extinct
A species dies out either by simply dying out or by evolving into another species.
extinct volcano
A volcano that has not erupted in recorded history, and is unlikely to erupt again.
extrusive
Igneous rocks that form at Earth’s surface from rapidly cooling lava.