Glossary Database

Select a Letter to view the associated terms.

 Glossary Term: 


 Earthquake  A series of elastic waves propagated in Earth, initiated where stress along a fault exceeds the elastic limit of the rock so that sudden movement occurs along the fault.
 Ecdysis  The act of losing or removing the dead, keratinous, outermost layer of epidermis. In snakes, the old skin is usually rolled off in one piece; in most other reptiles and amphibians it may come off in pieces, and is often pulled off with the teeth and then swallowed (Peters 1964).
 Echolocation  the process whereby the distance and direction of objects is determined by the reception of the reflection of an ultrasonic pulse (Morris 1992).
 Ecology  The study of relationships between organisms and their environments.
 Ecosystem  a local biological community and its pattern of interaction with its environment (Morris 1992).
 Ecotone  a transition zone between two distinct habitats that contains species from each area, as well as organisms unique to it (Morris 1992).
 Ectoparasites  types of parasites that live externally on their host; fleas and lice are obligate ectoparasites of man and animals (Morris 1992).
 Ectothermic  capable of maintaining body temperature by gaining outside heat outside itself (Morris 1992).
 Eddy  A little whirlpool or whirlwind.
 Ejecta  Rock fragments, glass, and other material thrown out of an impact crater or a volcano.
 Ejecta blanket  Rock material (crushed rock, large blocks, breccia, and dust) ejected from an impact crater or explosion crater and deposited over the surrounding area.
 El Nino  a complex set of changes in the water temperature in the Eastern Pacific equatorial region, producing a warm current; it occurs annually to some degree between October and February, but in some years intensifies and causes unusual storms and destruction of marine life and land ecosystems. (From Spanish for "the child;" meaning the Christ child; it typically begins at Christmas time) (Morris 1992).
 Elastic deformation  Temporary deformation of a substance, after which the material returns to its original size and shape. Example: the bending of mica flakes.
 Elastic limit  The maximum stress that a given substance can withstand without undergoing permanent deformation either by solid flow or by rupture.
 Elastic stress  Elastic deformation is a reversible, or nonpermanent change in a stressed rock. When the stress is removed, the rock returns to its original size and shape. There is an elastic limit though in which beyond that point the rock suffers permanent deformation and will not return to its original shape.
 Elastic-rebound theory  The theory that earthquakes result from energy released by faulting; the sudden release of stored strain creates earthquake waves.
 Electron  A negatively charged subatomic particle. Orbiting electrons comprise most of the volume of an atom.
 Electrostatic attraction  When two materials have opposite electrical charges, one negative and one positive, they are attracted to each other. Can get this result by rubbing the two materials together such as a rubber balloon rubbed on a carpet - when the balloon is then held near your head, it will make your hair move towards the balloon (the two materials are now oppositely charged).
 Element  The fundamental forms of matter.
 Elevation  The vertical distance from a datum (usually mean sea level) to a point or object on the Earth's surface.
 Ellipse  A closed curve in the form of a symmetrical oval.
 Embryo  1. the stage of multicellular organism that develops form a zygote before it becomes free-living. 2. specifically, in vertebrates, the period from after the long axis appears until all major structures are represented. In humans, this from about two weeks after fertilization to the end of the seventh or eighth week (Morris 1992).
 Emplacement  1. the process of intrusion of igneous rocks. 2. The localization of ore minerals by any process such as ore deposition.
 End moraine  A ridge of till that accumulates at the margin of a glacier.
 endangered species  A species which is in danger of imminent extinction.
 Endangered Species Act  regulation that protects species of animal or plant that has been identified as in danger of becoming extinct because of harmful human activity or environmental factors (Morris 1992).
 Endangered Species Act (ESA)  This is a federal law that first passed in 1973, and continues to be amended, revised and reauthorized today. The ESA was established to help protect U.S. species from extinction. Species whose populations are in genuine decline are listed as 'threatened species', while those whose populations become some low that they may go extinct are listed as 'endangered species'. Both listing prohibit any form of interference with these species other then approved conservation, protection and recovery efforts.
 Endemic  Native to a particular country, nation, or region (Guralnik 1970).
 Endothermy  term describing the internal generation of heat by mammals
 Entrenched meander  A meander cut into the underlying rock as a result of regional uplift or lowering of the regional base level.
 Eolian  Pertaining to wind.
 Eolian environment  The sedimentary environment of deserts, where sediment is transported and deposited primarily by wind.
 Eon  A major subdivision of geologic time consisting of eras. Example: Phanerozoic Eon. View timeline of geologic events.
 Ephemeral stream  A stream or portion of a stream which flows briefly in direct response to precipitation in the immediate vicinity, and who's channel is at all times above the water table.
 Epicenter  The area on Earth's surface that lies directly above the focus of an earthquake.
 Epidermis  The surface layer of the skin of a vertebrate (Halliday 1987).
 Epoch  A division of geologic time; a subdivision of a period. Example: Pleistocene epoch. View timeline of geologic events.
 Equator  An imaginary circle around the earth which is equally distant from the north pole and the south pole.
 Equidimensional  Equal in all directions.
 Equilibrium  In geology, a balance between form and process. For example the resistance of rocks along a coast and the erosional force of waves.
 Era  A division of geologic time; a subdivision of an eon. Example: Mesozoic Era. View timeline of geologic events.
 Eratosthenian Period  The period of lunar history when large craters, the rays of which are no longer visible, such as Eratosthenes, were formed (from 3.1 billion to 0.8 billion years ago).
 Erg  A large area covered with sand dunes. A sand sea such as those found in Earth's large deserts.
 Erosion  The processes that loosen sediment and move it from one place to another on Earth's surface. Agents of erosion include water, ice, wind, and gravity.
 Erratic  A large boulder carried by glacial ice to an area far removed from its point of origin.
 Eruptive fissure  An elongated fracture or crack at the surface of the Earth from which lava erupts. In some lava pours out quietly, forming broad plateaus like the Eastern Snake River Plain in Idaho.
 Escarpment  A cliff or very steep slope.
 Esker  A long, narrow, sinuous ridge of stratified glacial drift deposited by a stream flowing beneath a glacier in a tunnel or in a subglacial stream bed.
 Estivation  A state of dormancy, without movement or development, entered into by an insect to survive a hot or dry period. Also may be spelled as 'aestivation.'
 Estrous Cycle  the recurring periods of heat, or estrus, in the adult female of most mammals and the correlated changes in the reproductive tract from one period to the next (Morris 1992).
 Estrus  female mammals typically are receptive to mating with a male only when reproductive hormones and other physiological changes allow her to be receptive. Part of this process involves the release of an egg from the ovary (ovulation) which can then be fertilized by the male's sperm. Many of the larger mammals mate only once per year, thus the females reach the state of estrus just once, when they mate. Many small mammals, such as the mice, mate more than once each year, thus the females reach estrus more than once each year.
 Estuary  A bay at the mouth of a river formed by subsidence of the sand or by a rise in sea level. Fresh water from the river mixes with and dilutes seawater in an estuary.
 Eustatic change of sea level  A worldwide rise or fall in sea level resulting from a change in the volume of water or the capacity of ocean basins.
 Evaporation  When liquid is changed into a vapor.
 Evaporite  A rock composed of minerals derived from evaporation of mineralized water. Examples: rock salt, gypsum.
 Everscible tubercle  A kind of tentacle housed within the body of some caterpillars, at the rear. If the caterpillar feels threatened by a potential predator, it can be pushed out to release a chemical, which mimics an ant alarm pheromone. This scent causes the ants to become aggressive and the potential predator either leaves or the ants attack it.
 Evolution  1.) Physiological, morphological and/or genetic changes that take place in animal and plant species, over millions of years. 2.)All mammals and other living organisms change through time. Evolution specifically refers to change in organisms that is genetic; that is, frequencies of specific genes in the organism's genetic makeup change. This results in changes in genetic characteristics.
 Ewe  an adult female sheep (Morris 1992).
 Exfoliation  A weathering process by which concentric shells, slabs, sheets, or flakes are successively broken loose and stripped away from a rock mass.
 Exoskeleton  an external covering or integument, esp. when hard, as the shell of crustaceans (Stein 1966).
 Exposure  Bedrock not covered with soil or regolith; outcrop.
 Extant  in existence; still existing; not destroyed or lost (Stein 1966).
 Extension (fault)  An extensional fault is one whose displacement results in extension of the layers that the fault cuts.
 Extinction  1.) The disappearance of an entire species, wherein every individual in the given species dies. 2.) The process of becoming extinct; dying out or coming to an end (Morris 1992).
 Extirpation  removing, destroying, pulling up extermination or otherwise making extinct (Morris 1992).
 Extrusion  To be forced out through a small opening. To protrude.
 Extrusive  igneous rock that has been erupted onto the surface of earth
 Extrusive rock  A rock formed from a mass of magma that flowed out on the surface of Earth. Example: basalt.
 eyed egg  The embryonic stage at which pigmentation of the eyes becomes visible through the egg shell.
 Eyespot  A mark found on some caterpillars and butterflies. It is round and has a spot in the center (the pupil) of a different color.