Historical Geology
pluton(PLUE-ton) an underground body of igneous rock younger than the
rocks that surround it; it is formed where molten rock assimilates older
rocks
prebiotic conditions on the early Earth prior to the introduction of life
processes
precipitation the deposition of minerals from seawater
primary producer the lowest member of a food chain
primordial pertaining to the primitive conditions that existed during early
stages of development
prokaryote(pro-KAR-ee-ote) a primitive organism that lacks a nucleus
protist(PRO-tist) a unicellular organism, including bacteria, protozoans,
algae, and fungi
pseudofossil a fossil-lik e body such as a concretion
pterosaur(TER-eh-sore) extinct Mesozoic flying reptiles with batlike wings
radiolarian a micr oorganism with shells made of silica comprising a large
component of siliceous sediments
radiometric dating the age determination of an object by radiometric and
chemical analysis of stable versus unstable radioactive elements
redbed a sedimentary rock cemented with iron oxide
reef the biological community that lives at the edge of an island or conti-
nent;the shells from dead organisms form a limestone deposit
re gression a f all in a sea level, exposing continental shelves to erosion
reptile an air-breathing, cold-blooded animal that lays eggs and is usually
covered with scales
Rodinia a Pr ecambrian supercontinent whose breakup sparked the Cam-
brian explosion of species
sandstone a sedimentary rock consisting of sand grains cemented together
sedimentary rock a r ock composed of fragments cemented together
shale a fine-grained fissile sedimentary r ock of consolidated mud or clay
shield areas of the exposed Precambrian nucleus of a continent
species groups of organisms that share similar characteristics and are able to
breed among themselves
spherules small, spherical,glassy grains found on certain types of mete-
orites, on lunar soils, and at large meteorite impact sites
strata layered rock formations; also called beds
stromatolite(STRO-mat-eh-lite) a calcareous structure built by successive
layers of bacteria or algae and that have existed for the past 3.5 billion
years
subduction zone a r egion where an oceanic plate dives below a conti-
nental plate into the mantle; ocean trenches are the surface expression of
a subduction zone