Relative Dating
Notes
Relative Dating
Relative dating is used to arrange geological
events, and the rocks they leave behind, in a
sequence. The method of reading the order
is called stratigraphy (layers of rock are
called strata). Relative dating does not
provide actual numerical dates/ages for the
rocks.
Relative Age
is the “age” of a
rock or strata
compared to the
ages of other
rocks or strata.
Relative Age
Principle of Superposition
as sedimentary
rocks form, they
are deposited on
older rock layers.
Principle of Superposition
in undisturbed
layers, the oldest
is on the bottom
and higher layers
are younger.
Principle of Superposition
Oldest layer is on bottom (1)
Principle of Superposition
The Grand Canyon
Principle of Superposition
The Grand Canyon
Principle of original
horizontality
The law states that
layers of sediment
were originally
deposited horizontally
under the action of
gravity.
Principle of Fossil
Succession.
Also known as the principle of faunal
succession, is based on the observation that
sedimentary rock strata contain fossilized
flora (plants) and fauna (animals), and that
these fossils succeed each other vertically in
a specific, reliable order that can be identified
over wide horizontal distances.
Principle of CrossCutting Relationships
An igneous/metamorphic
rock, fault, or other
geologic feature must
be younger than any
rock across which it
cuts..
Crosscutting
Relationships
•
•
•
•
•
•
•
Faults
Folds
Intrusions
Extrusions
Unconformities
Nonconformities
Disconformities
Video
https://www.youtub
e.com/watch?v=D
wwk1KdWn9c
Relative Dating: Flashback
Flashback:
List the
principles of
Relative
dating that
apply
to the cross
section on
the right
Uniformitarianism
is the idea that the
processes
occurring on earth
today are similar to
those that occurred
in the past.
Uniformitarianism
basically says
“The present is
the key to the
past.”
Uniformitarianism
is the idea that
geological
features formed
slowly over long
periods of time.
Uniformitarianism
claims the Earth is
4.6 billion years
old.
What does the Principle of
Superposition say?
1.
2.
3.
4.
Sedimentary rocks form in rivers
Igneous rocks form faster than sedimentary
New rock layers form on top of older ones
There are billions of fossils on Earth
Which layer of
rock is the oldest?
1.
2.
3.
4.
5.
1
2
3
4
They are all the same
age
HOW OLD WOULD MOST GEOLOGISTS SAY THE
EARTH IS?
1.
2.
3.
4.
6000 years
75,000 years
20 million years
4.6 billion years
According to what theory, is the earth
4.6 billion years old?
1.
2.
3.
4.
Catastrophism
Uniformitarianism
Geologism
Agism
Relative Dating
Notes
Extrusions
are igneous
rock layers that
form on the
surface when
lava hardens.
Extrusions
are always
younger than
the layers over
which they form.
Extrusion
Kubu Rock – Botswana, Africa
Intrusions
are igneous
rocks that form
when magma
pushes up into
rock layers.
Intrusions
are always
younger than
the rock layers
they invade.
Intrusion
Intrusion
Intrusion
Devil’s Tower, WY
Intrusion
Devil’s Tower, WY
Stop and Summarize
Stand-up, Hand-up, Pair-up: Create a
Venn Diagram with your partner.
In the image below identify as many
intrusions and extrusions as you can!
Faults
are breaks in the
earth’s crust. A
fault is always
younger than
the rock it cuts
through.
Faults
Faults
Shoshone Fault, CA
Folds
occur when
rock layers are
compressed
together and
bend or curve.
Folds
Guadalajara, Spain
Folds
Mojave Desert, CA
Stop and Summarize
Write-Pair-Share: Create a Venn-Diagram
comparing Faults and Folds.
Identify the
CrossCutting
Relationships
2
1
3
Flashback
SOME Relative
Dating Practice
Write the correct order of events by
numbering their occurrences.
Identify the cross-cut relationships
in each cross section.
Relative Dating
Relative Dating
Relative Dating
Relative Dating Example
Unconformities
are gaps in the
rock sequence
(caused by the
erosion of rock
layers).
Angular Unconformity
occur when rock
layers are tilted or
uplifted, and then
worn down by
erosion and
weathering.
Sediments are then deposited
on top of these eroded layers.
Angular Unconformity
Angular Unconformity
Disconformities
are gaps created
when erosion
occurs on an
overlying rock
layer.
Disconformity
Nonconformity
are formed when
sedimentary rock
overlays igneous
or metamorphic
rocks.
Nonconformity
Flashback
What type of
unconformity is E
in the image to
the right? List
any cross-cutting
relationships and
order the events
from oldest to
youngest.
E
Write a Sequence of event for the following
geologic cross-section:
Draw the following geologic cross-section:
1.) 2 layers of sedimentary rock form.
2.) An extrusion forms on top of the two layers.
3.) A 3rd layer of sedimentary rock forms.
4.) An intrusion cuts through all of the rock
layers, but not to the surface.
5.) A 4th layer of sedimentary rock forms.
Draw the following geologic cross-section:
1.) 2 layers of sedimentary rock form
2) Layers 1-2 are folded
3.) A 3rd sedimentary layer forms.
4.) A normal fault cuts through all the layers
5.) A 4th sedimentary layer forms.
6.) An intrusion cuts all the way to the surface
forming an extrusion.
Top half of paper = Geologic History
Must Include: At least…
• 5 sedimentary rock layers
• 3 different cross-cutting relationships
• 1 disconformity
Bottom half of paper = Geologic Cross Section
• You will draw a geologic cross section numbering
the sedimentary layers and lettering cross-cutting
relationships. Also identify the type of
unconformity.
Correlation
is using rock and
fossil evidence
to match up
dating at different
locations.
Correlation
Index Fossils
are used for
dating the rock
layers in which
they are found.
Index Fossils
are species that
were abundant all
over the earth, but
existed for shorter
periods of time.
Index Fossil
trilobite
Index Fossil
ammonite
Index Fossil
Correlation using index fossils
Index Fossil
Correlation using index fossils
Exit Slip
If humans went extinct in the near
future, would we make good
index fossils? Explain your
answer!
Hints: use your timescale, and the
definition of index fossils.
What kind of crosscut is shown to the
right?
0%
0%
0%
0%
1.
2.
3.
4.
Intrusion
Extrusion
Folds
Unconformity
What kind of
cross-cut is shown
to the right?
0%
1. Intrusion
0%
2. Fault
0%
3. Fold
0%
4. Angular Unconformity
What kind of
cross-cut is shown
to the right?
0%
1. Intrusion
0%
2. Fault
3. Fold
0%
4. Angular Unconformity
0%
What is the name of the type of
fossil is used to correlate rock
layers at two or more different
locations?
0%
1. Mold
2. Petrified fossil
0%
3. Index fossil
0%
4. Trace fossil
0%
Using correlation, Which
two layers would you
determine to be of the
same age?
0%
0%
0%
0%
1.
2.
3.
4.
A&D
A&B
B&D
B&E
Paleontology Notes
READY YOUR REMOTE
FOR A QUICK REVIEW
What type of
cross-cut appears
at location e?
0%
0%
0%
0%
1.
2.
3.
4.
Fault
Fold
Nonconformity
Angular Unconformity
What type of crosscut appears in the
picture?
0%
0%
0%
0%
1.
2.
3.
4.
Fault
Disconformity
Nonconformity
Angular Unconformity
Absolute Age
is the age in years
of a rock or other
object (as
determined by
radiometric
dating.
Radiometric Dating
entails finding the
amount of certain
radioactive
elements left in a
rock or object.
Journal
TURN TO YOUR JOURNAL PAGE
Write a geologic history that explains the
order of occurrence of each event.
Draw a geologic cross-section with the following:
1.) At least 3 sedimentary rock layers
2.) At least 3 cross-cuts
(faults, folds, intrusions,
extrusions, or unconformities,
angular unconformities,
nonconformity, disconformity)
Journal #5
Paleontology Notes
READY YOUR REMOTE FOR A
QUICK REVIEW
Which of the
following is
oldest?
0%
1.
0% 2.
0% 3.
0% 4.
Sandstone B
Sandstone A
Earthquake fault
Igneous Dike B
What type of
cross-cut appears
at location e?
1. Fault
0%
2. Fold
0%
3. Nonconformity
0%
4. Angular Unconformity
0%
What type of crosscut appears in the
picture?
1. Fault
0%
0%
2. Disconformity
0%
3. Nonconformity
0%
4. Angular Unconformity
“The important thing is to never
stop questioning.”
- Albert Einstein
How much do you know about
Paleontology?
Pre-Unit Questions
(Post-Unit)
Answer the following
True/False Questions
How much do you know about
Paleontology?
Pre-Unit Questions
(Post-Unit)
Answer the following
True/False Questions
Many scientists theorize
that dinosaurs were wiped
out many years ago by
some great catastrophe.
0%
0%
1. True
2. False
How much do you know about
Paleontology?
TRUE. Obviously dinosaurs
don’t exist today and they seem
to disappear suddenly from the
fossil record.
Fossils take millions of
years to form.
0%
0%
1. True
2. False
How much do you know about
Paleontology?
TRUE or FALSE?
FALSE. Fossils can form in less
than a year depending on the
conditions.
There are billions of fossils
found all over the earth.
0%
0%
1. True
2. False
How much do you know about
Paleontology?
TRUE. There are many fossils
buried in the rock all over the
planet. Over 99% of them are
small marine plants and animals.
Dinosaurs are “giant
lizarDs.”
0%
0%
1. True
2. False
How much do you know about
Paleontology?
FALSE. Some were large, but
many were not. The term dinosaur,
coined in the 1800’s, does mean
“terrible lizard,” but the average
size of a dinosaur was that of a
large dog.
JOURNAL # 6
Describe & discuss at
least three new facts
that you learned about
paleontology while
studying this unit.
RETURN YOUR REMOTE
Classwork Assignments
1.) Journal # 6
2.) Relative Dating Geologic CrossSections WS
3.) Paleontology Test Review
Partner Assignment
1.) Draw a geologic Cross-Section
on a blank piece of paper
2.) Include at least 5 sedimentary
layers & 3 cross-cuts (intrusions,
extrusions, faults, folds, or
unconformities)
3.) Swap with a friend & have
him/her number the events