Glossary Starting with the letter: E


A sudden motion or trembling of the Earth’s crust caused by the passage of seismic waves radiated from a fault along which sudden movement has occurred.

El NiΓ±o

A climactic event that generally occurs every four to twelve years, in which warming of the ocean surface off the western coast of South America disrupts the normal pattern of the upwelling of cold, nutrient-rich water. It causes fish and plankton to die and affects weather over much of the Pacific Ocean and around the world.


Negatively charged atomic particle.

Electron Microscope

A type of microscope that uses electrons rather than visible light to produce magnified images.


A substance composed of atoms having an identical number of protons in each nucleus. An element cannot be separated into simpler substances by chemical means. A trace element is one present in only small quantities, less than 0.1 percent by weight.


The height of an object above a particular reference level, usually sea level.

Elliptical Orbit

A planetary orbit that traces an elliptical course.


The complex group of related process by which rock is broken down physically and chemically and the products are moved. Agents of erosion include water, wind, and ice, as well as biological processes.


The ability of a material to irreversibly deform without rupture.


A cell that possesses a defined nucleus surrounded by a membrane. Protists, fungi, plants, and animals are eukaryotes.


The branch of biology that deals with of the origin and distribution of possible life on other planetary bodies.


The process by which one distinct phase of matter separates from another.


Occurring or originating away from Earth and its atmosphere.