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supernova an enormous stellar explosion in which all but the inner core of
a star is blown off into interstellar space
tectonic activity the formation of Earth’s crust by large-scale movements
throughout geologic time
tephra(TEH-fra) solid material ejected into the air by a volcanic eruption
terrestrial all phenomena pertaining to Earth
Tethys Sea(THE-this) the hypothetical midlatitude region of the oceans
separating the northern and southern continents of Laurasia and Gond-
wana several hundred million years ago
tetrapod a four-footed vertebrate
thecodont(THEE-keh-daunt) an ancient primitive reptile that gave rise to
dinosaurs, crocodiles, and birds
therapsid(the-RAP-sid) ancient reptile ancestors of the mammals
therian animals that have live births such as mammals
thermophilic relating to primitive organisms that live in hot-water
environments
tide a bulge in the ocean produced by the Sun’s and Moon’s gravitational
forces on Earth’s oceans; the rotation of Earth beneath this bulge causes
the rising and lowering of the sea level
till nonstratified material deposited directly by glacial ice as it recedes and
consolidated into tillite
tillite a sedimentary deposited composed of glacial till
transgression a r ise in sea level that causes flooding of the shallow edges of
continental margins
trilobite(TRY-leh-bite) an extinct marine arthropod, characterized by a
body divided into three lobes, each bearing a pair of jointed appendages,
and a chitinous exoskeleton
tundra permanently frozen ground at high latitudes of the Arctic regions
type section a sequence of strata that was originally described as constitut-
ing a stratigraphic unit and serves as a standard of comparison for iden-
tifying similar widely separated units
ultraviolet the invisib le light with a wavelength shorter than visible light
and longer than X rays
varves thinly laminated lake bed sediments deposited by glacial meltwater
vertebrates animals with an internal skeleton, including fish, amphibians,
reptiles, and mammals
volcanism any type of volcanic activity
volcano a fissur e or vent in the crust through which molten rock rises to
the surface to form a mountain
zooplankton small, free-floating or poorly swimming marine or freshwater
animal life
287Glossary