Cornell Notes: Relative-Age Dating Powerpoint Notes
Focus Questions:
How can you tell if one rock is older than another?
How can you tell if one fossil is older than another?
Uniformitarianism
States that the geologic processes occurring today have
been occurring since Earth formed.
Give two examples:
1.
2.
Relative-age dating
1. Scientists learn about the past by studying the order in
which geologic events occurred by using relative-age dating.
2. It is a process by which rocks are placed in their proper
sequence or order.
3. Determines only the chronological order of events, not
the absolute age in years.
What methods do
scientists use to
determine relative
ages of rocks and
fossils?
1.
2.
3.
4.
original horizontality
superposition
cross-cutting relationships
inclusions
1. What is original
horizontality?
1. sedimentary rocks are deposited in horizontal or nearly
horizontal layers over millions of years.
Give one example of where this can clearly be seen:
2. What is
superposition?
2. In an undisturbed rock sequence, the oldest rocks are at
the bottom and each layer above is younger than the layer
beneath it.
3. What does crosscutting
relationships show?
3. An intrusion is younger than the rock it cuts across.
(Intrusion: hot magma is pushed up through cracks in
existing rock layers.)
4. What is an
inclusion?
4. Fragments of rocks, called inclusions, are older than the
rocks that contain them.
What are
unconformities in
rock layers?
Rock layers have been eroded and new layer(s) of sediment
have been deposited. This creates a gap in the rock record.
List the three types
of unconformities?
Disconformity
Nonconformity
Angular unconformity
Disconformitylayers d, e, and f have
been eroded and
layers g and h have
been deposited after
erosion.
Nonconformity-
h
g
c
b
a
when a layer of sedimentary rock is deposited over igneous
or metamorphic rock
Angular
Draw the example given in the powerpoint below:
Unconformity1.
2.
when sedimentary
rock is deposited on
top of tilted and
eroded layers
(mountain building
uplifts sedimentary
rock and exposes it to
weathering and
erosion)
3.
4.
What is correlation?
Matching of rock layers or fossils in one region to another
region
Write three
summary sentences
about the above
information.
1.
2.
3.