Unit 3 Review
Please see pages 145-194 in your book for more
information
*This study guide is just to get you started
studying– please look at your notes and book
too.*
What is uniformitarianism?
• A principle that geological processes that
occurred in the past can be explained by
current geologic processes.
What is climate?
• The weather conditions in an area over a long
period of time.
What is a fossil?
• The trace or remains of an organism that lived
long ago, most commonly preserved in
sedimentary rock.
What is a trace fossil?
• A fossilized structure, such as a footprint or
coprolite, that formed in sedimentary rock by
animal activity on or within soft sediment.
What is an ice core?
• A long cylinder of ice obtained from drilling
through ice caps or ice sheets; used to study
past climates.
How do organisms become preserved
as fossils?
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Fossils can be trapped in amber or asphalt
Buried in rock
Become frozen
Become petrified
What can fossils tell us?
• Fossils tell scientists about changes to the
environment
• Fossils tell scientist how life forms have
changed over time
How does sedimentary rock show
Earth’s history?
• The composition of sedimentary rock show
the source of the sediment that makes up the
rock
• The texture of the sedimentary rock shows the
environment in which the sediment was
carried and deposited
• Features in the rock show what was
happening to the sedimentary rock
What do Earth’s surface features tell
us?
• How continents move
• How landforms change over time
What other materials tell us about
Earth’s climate history?
• Trees
• Sea-Floor sediments
• Ice cores
What is relative dating?
• Any method of determining whether an event
or object is older or younger than other
events or objects.
What is superposition?
• A principle that states that younger rocks lie
above older rocks if the layers have not been
disturbed.
What is unconformity?
• A break in the geologic record created when
rock layers are eroded or when sediment is
not deposited for a long period of time.
What is a geologic column?
• An ordered arrangement of rock layers that is
based on the relative ages of the rocks and in
which the oldest rocks are at the bottom.
How are undisturbed rock layers
dated?
• Older layers are on the bottom
• Younger layers are on the top
How are sedimentary rock layers
disturbed?
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Tilting
Folding
Faults and Intrusions
Unconformities
How are rock layers ordered?
• Law of crosscutting relationships states that:
“A fault or a body of rock, such as an intrusion,
must be younger than any feature or layer of
rock that the fault or rock body cuts through.”
How are fossils used to determine
relative ages of rocks?
• Fossils can help us determine the relative age
of rocks by giving us a reference point for the
rocks.
• Younger fossils= younger rocks
• Older fossils= older rocks
What is absolute dating?
• Any method of measuring the age of an event
or object in years.
What is radioactive decay?
• The process in which a radioactive isotope
tends to break down into a stable isotope of
the same element or another element.
What is half-life?
• The time required for half of a sample of a
radioactive isotope to break down by
radioactive decay to form a daughter isotope.
• If you have 6 milligrams of the original isotope
in one half-life 3 milligrams of the isotope
would be left and 3 milligrams would be the
daughter isotope
What is radiometric dating?
• A method of determining the absolute age of
an object by comparing the relative
percentages of a radioactive parent isotope
and a stable daughter isotope.
How can the absolute age of rock be
determined?
• Thru absolute dating methods
What is the best rock for radiometric
dating?
• Igneous rock
What are some radiometric dating
methods?
• Radiocarbon dating
• Potassium-Argon dating
• Uranium-Lead dating
How is radiometric dating used to
determine the age of Earth?
• Radiometric dating can be done on meteorites
to determine the age of the Earth.
How are index fossils used?
• Index fossils are markers for the time that
organisms lived on Earth
• Index fossils can date different layers of Earth