Historical Geology
Archaeopteryx (AR-key-op-the-riks) a primitive Jurassic crow-sized bird
characterized with teeth and a bony tail
archea (AR-key-ah) a primitive bacteria-like organism living in high-
temperature environments
Archean(AR-key-an) a major eon of the Precambrian from 4.0 to 2.5 bil-
lion years ago
arthropod (AR-threh-pod) the largest group of invertebrates, including
crustaceans and insects, characterized by segmented bodies, jointed
appendages, and exoskeletons
asteroid a r ocky or metallic body, orbiting the Sun between Mars and
Jupiter, and leftover from the formation of the solar system
asteroid belt a band of asteroids orbiting the Sun between the orbits of
Mars and Jupiter
Azoic eon a ter m applied to the first half-billion years of Earth’s history
Baltica(BAL-tik-ah) an ancient Paleozoic continent of Europe
bar rier island a low , elongated coastal island that parallels the shoreline and
protects the beach from storms
basalt(bah-SALT) a dark volcanic rock rich in iron and magnesium and
usually quite fluid in the molten state
batholith(BA-tha-lith) the largest of intrusive igneous bodies and more
than 40 square miles on its uppermost surface
bedrock solid layers of rock lying beneath younger material
belemnite(BEL-em-nite) an extinct Mesozoic cephalopod with a bullet-
shaped internal shell
bicarbonate an ion created by the action of carbonic acid on surface rocks;
marine organisms use the bicarbonate along with calcium to build sup-
porting structures composed of calcium carbonate
big bang a theor y for the creation of the universe, dealing with the initia-
tion of all matter
biogenic sediments composed of the remains of plant and animal life such
as shells
biomass the total mass of living organisms within a specific habitat
biosphere the living portion of Earth that interacts with all other biologic
and geologic processes
bivalve a mollusk with a shell comprising two hinged valves, including oysters,
muscles,and clams
black smoker superheated hydrothermal water rising to the surface at a
midocean ridge;the water is supersaturated with metals, and when exit-
ing through the seafloor, the water quickly cools and the dissolved met-
als precipitate, resulting in black, smokelike effluent
blastoid an extinct Paleozoic echinoderm similar to a crinoid with a body
resembling a rosebud