Page 97 - The Restless Earth Fossils

6 Fossils

steno, nicolaus Seventeenth century scientist who recognized
fossils as the remains of once-living creatures and who out-
lined basic geological processes.
strata Rock layers.
stromatolites Fossilized colonies of primitive organisms
called cyanobacteria.
subsided Sunken.
tar pits Holes filled with thickened natural asphalt produced
by organic sediments.
terrestrial Pertaining to dry land.
tetrapods Four-legged animals.
theropods Predatory dinosaurs that walked on two legs, like
T. rex.
topography The shape of the land, including mountains,
valleys, and plains.
trace fossil Anything a living creature leaves behind as fossils,
such as tracks and droppings.
uniformitarianism Theory that geological forces acted in the
past much as they do today.
united states geological survey (usgs) Government
agency that maps and surveys geological features in the
United States.
uplift Rising of large landmasses.
uranium Radioactive element used for geological time
measurements.
vestigial organs Organs that no longer perform their original
function.
volcanic ash Soot produced by erupting volcanoes.
x-rays Radiation produced when the atoms of an element
emits subatomic particles.

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