earthquake the sudden rupture of rocks along active faults in response to
geologic forces within Earth
East Pacific Rise a midocean ridge spreading system running north-south
along the eastern side of the Pacific; the predominant location where hot
springs and black smokers were discovered
echinoderm(I-KY-neh-derm) marine invertebrates, including starfish, sea
urchins, and sea cucumbers
echinoid(I-KY-noid) a group of echinoderms including sea urchins and
sand dollars
ecliptic the plane of Earth’s orbit around the Sun
ecology the interrelationships between organisms and their environment
ecosystem a comm unity of organisms and their environment functioning
as a complete, self-contained biological unit
Ediacaran a g roup of unique, extinct, late-Precambrian organisms
environment the complex physical and biological factors that act on an
organism to determine its survival and evolution
eon the longest unit of geologic time, roughly about 1 billion years or more
in duration
epoch a geolo gic time unit shorter than a period and longer than an age
era a unit of geologic time below an eon, consisting of several periods
erosion the wear ing away of surface materials by natural agents such as
wind and water
erratic a glacially deposited boulder far from its source
esker a long narrow ridge of sand and gravel from a glacial outwash stream
eukaryote(yu-KAR-ee-ote) a highly developed organism with a nucleus
that divides genetic material in a systematic manner
eurypterid (yu-RIP-te-rid) a large Paleozoic arthropod related to the
horseshoe crab
evaporite the deposition of salt, anhydrite, and gypsum from evaporation in
an enclosed basin of stranded seawater
evolution the tendency of physical and biological factors to change with time
exoskeleton the hard outer protective covering of invertebrates including
cuticles and shells
extinction the loss of large numbers of species over a short duration, some-
times marking the boundaries of geologic periods
extrusive(ik-STRU-siv) an igneous volcanic rock ejected onto Earth’s surface
family in systematics, the category of plants and animals under order and
comprising several genera
fault a break in crustal rocks caused by Earth movements
feldspar a g roup of rock-forming minerals comprising about 60 percent of
Earth’s crust and an essential component of igneous, metamorphic, and
sedimentary r ock
Glossary