Download Fossils Test Study Guide

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A Trip Through Geologic Time Test Study Guide
fossil- imprints, remains, or traces of once-living organisms that have been preserved; usually
found in sedimentary rock
conditions necessary for fossils to form- 1. must be a once-living organism 2. must be buried
quickly 3. must be protected from scavengers or microorganisms 4. must have hard parts
(teeth, shells, bones)
fossils can give information about- the environment, climate, and animal behavior as well as
dating rocks
Type of Fossil
How it’s Formed
petrified
are hard and rocklike; some or all of the remains have
remains
been replaced by minerals (i.e. quartz replacing calcium in
bones)
carbon films
the organism is exposed to pressure and heat which forces
gases and liquids out from the organism. A thin film of
carbon is left forming an outline of the original organism.
molds and
casts
holes in rock let water and air reach the shell or hard part
causing it to dissolve and leave behind a hollow part
called a mold. Later the other sediments fill in the hollow
part and harden into rock to make a cast.
preserved
remains
actual organisms are found trapped in amber, frozen
ground, glacial ice, or tar seeps
trace fossils
fossilized tracks and other evidence of animal activity
index fossils
lived on Earth for a short period of time, were abundant
(many), and were widespread geographically (everywhere)
Example
law of superposition- states that for undisturbed rock layers, the
oldest rocks are on bottom and become younger and younger toward
the top.
relative dating- used in geology to determine the comparative age of
rocks by examining the position of the rock layers. i.e. top layers are younger than bottom
layers, bottom layers are older than top layers, etc.
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extrusion- lava that hardens on the earth’s surface; always
younger than the rocks below it
intrusion- magma that cools and hardens in a mass of
igneous rock below the earth’s surface; always younger than
the rock layers around and beneath it
fault- a break in the earth’s crust
unconformity- gaps in rock layers; a place where new rock
layers meet much older rock surface beneath them
absolute dating- a method used to determine the age in years of a rock or other object. It
uses the properties of atoms in rocks and other objects to find their ages.
radioactive decay- the atoms of one element break down to form atoms of another element;
used to determine the absolute ages of rocks
half-life- the time it takes for half of the atoms of an isotope to decay (Carbon-14 = 5730
years)
Carbon-14 dating- Carbon-14 has a long half-life (5730 years). Because every living thing has
carbon in it, the amount of carbon-14 remaining in a dead organism can be measured to
determine the age of the fossil.
Time in years
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