abyss the deep ocean, generally over a mile in depth
Acanthostega (ah-KAN-the-stay-ga) an extinct primitive Paleozoic
amphibian
accretion the accumulation of celestial gas and dust by gravitational attrac-
tion into a planetesimal, asteroid, moon, or planet
age a geologic time interval smaller than an epoch
albedo the amount of sunlight reflected from an object and dependent on
the object’s color and texture
alluvium(ah-LUE-vee-um) stream-deposited sediment
alpine glacier a mountain glacier or a glacier in a mountain valley
amber fossil tree resin that has achieved a stable state after ground burial via
chemical change and the loss of volatile constituents
ammonite(AM-on-ite) a Mesozoic cephalopod with flat,spiral shells
amphibian a cold-blooded,four-footed vertebrate belonging to a class
midway in evolutionary development; fish and reptiles
andesite a v olcanic rock intermediate between basalt and rhyolite
angiosperm(AN-jee-eh-sperm) a flowering plant that reproduces sexu-
ally with seeds
annelid(A-nil-ed) a wormlike invertebrate characterized by a segmented
body with a distinct head and appendage
archaeocyathan(AR-key-ah-sy-a-than) an ancient Precambrian organism
resembling sponges and coral; it built early limestone reefs
GLOSSARY