Page 94 - The Restless Earth Fossils

glossary 3

evolution Transformation of species over time through muta-
tion and natural selection.
extinction Permanent loss of a species of organism.
Formations Groups of rocks of similar appearance and origin.
Fossils The physical remains or traces of once-living things,
usually mineralized.
geological maps Maps designed to show the geological fea-
tures of an area.
geological time Time spans long enough to measure moun-
tain building and other geological processes.
geology The scientific study of rocks, minerals, and geological
forces.
green river Formation Fossil-rich rocks of a region in the
American West formed by an ancient system of freshwater
lakes.
grid method Dividing a fossil dig site into squares in order to
map discoveries.
hadrosaurs Vegetarian “duck-billed” dinosaurs of the Creta-
ceous Period.
hominins Fossil primates believed to be the ancestors of mod-
ern humans.
horizons Distinctive layers of rock within a formation.
igneous rocks Rocks formed under extreme heat and
pressure.
index fossils Fossils useful in marking relatively short inter-
vals of geological time.
iridium Rare element used as a marker for impacts of large
meteors and asteroids (in which iridium is abundant).
Kt boundary Boundary between the Cretaceous and Tertiary
periods.
living fossils Animals currently alive that closely resemble
fossil species.
lycopods Primitive plants that grew to tree size during the
Paleozoic Era.

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