Warm Up/DO NOW
1.
2.
3.
What causes geologic change
(changes to the land) on earth?
What are the 3 types of plate
boundaries?
Which plate boundary causes sea
floor spreading?
LEARNING WITH A FOCUS
Student Learning Map
Unit 1: Earth’s History
Concept 3: Dating the Earth
What information do humans get
from rock layers, index fossils, and
ice cores in order to paint a picture
of Earth’s History?
Student Objectives

By the end of this lesson students will
be able to….



Identify the difference between absolute
and relative age
Determine the relative age of a rock
using the law of superposition and index
fossils
Explain how ice cores help scientists
study how Earth’s climate was in the past
Vocabulary

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Relative Age
Absolute Age
Law of Superposition
Igneous Inclusion
Index Fossil
Unconformity
Agenda
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Do Now (15 min.)
LEQ #3 Assessment (15 min.)
Activator: Student Line (8 min.)
Absolute vs. Relative T-Chart (12 min.)
Sandwich Demo (10 min.)
Group Challenge (10 min.)
Law of Superposition Notes (15 min.)
Ticket Out (5 min.)
Activator: Student Line Up
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I need 7 volunteers
What is the exact
position of _______
in the line?
What is an estimate
of _______ in the
line?
What is the
difference between
exact and estimate?
SOOO…..


Looking at our list
of vocabulary
words, which do
you think means
exact?
Which of our
vocabulary words
do you think means
estimate?

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
Relative Age
Absolute Age
Law of
Superposition
Igneous Inclusion
Index Fossil
Unconformity
Absolute vs. Relative Age
(Draw a T Chart in your Notebook)




Relative Age
Determining the age of
an object in relation to
other objects
“Estimate”
Index Fossils, Rock
layers
Example: A friend tells
you she has 2 brothers –
one that’s older than her
and one that’s younger




Absolute Age
Determining the actual
age in years of an object
“Exact”
Radiometric dating, half
life, radioactive decay
Example: I have one
brother who is 8 years
old and one who is 17
years old
Mnemonic Memory Help
When you hear these two terms, think…
Absolute = exact
Relative = estimate
How old is old?
Scientists use several strategies to
determine age of rocks and fossils.
1. Absolute Age: actual age of an object
or how long ago an event occurred
by using radioactive dating.
2. Radioactive Dating: measures age
by comparing the amount of
radioactive element isotope
present to how much is normally
present in that material
3. Relative Age: age of an object
compared to another- “I am older
than you”
Absolute Age
Half life; the amount of time (years) it
takes for 1/2 of the radioactive
isotope to decay by 1/2, indicates the
age of the object.
12
Radiometric Dating
1. What does it mean when we say an atom has
“decayed”?
2. At the end of each half-life, at approximately what
percentage are the atoms “decaying”?
3. Does the amount of time you shake the box affect
the outcome?
4. Do the number of atoms you start with affect the
outcome? Explain.
5. How do scientists use radioactive decay to date
fossils and artifacts?
14
HOT Q 1: 4 Corners
What is the difference between relative
dating and absolute dating?
a.
b.
c.
d.
Relative dating provides the exact age of a rock while
absolute dating provides a rough estimate of the rocks
age.
Relative dating can estimate a rocks age only in relation
to other objects and events while absolute dating can
provide the actual age
Relative dating uses several types of radioactive decay
to determine an objects relative age while absolute
dating only uses the half of uranium 235
Relative dating and absolute dating can only determine
the rocks age in relation to other objects or events
So… Why Do We Care?
 Relative
 The
and Absolute Dating tell us…
age of the Earth as well as its history
 When the dinosaurs roamed the earth
 How the Earth was and where it is going
DO NOW (5 min)

1. List these eras in order from oldest to
youngest (the present!): Mesozoic,
Precambrian, Cenozoic, Paleozoic.

2. When did life first appear on Earth?
During what era did this occur?
Now that we know how to date
the earth, lets start dating!
 Sandwich
Demonstration
Each of you will be in charge of “a
piece” of the sandwich
 As soon as I place your piece in
the sandwich, start counting
(silently)

Sandwich Demo Cont’d
Drawing:
Which
ingredient is the
So basically what you are
oldest?
saying is that the oldest
Which is on
layer of thesandwich
ingredient is the
the bottom
youngest?
AND
The youngest
layer
at
 How
doisyou
the top
know?

Which layer do you think is the
oldest and youngest?
Law of
Superposition
Says: “ The rocks
at the bottom are
OLDER than the
rocks above”


It can be difficult to
determine a rocks
absolute age. So…
scientists use the law
of superposition.
According to the law
of superposition, in
horizontal
sedimentary rock
layers the oldest
layer is at the bottom.
Each higher layer is
younger than the
layers below it.
The Position of
Rock Layers
Cornell Notes

What is the
Law of
Superposition?


In an undisturbed rock
layer, the layer of rock
on the bottom is
OLDER than the
layers above it.
Makes Sense: Older
sediments must be
laid down before the
younger ones can pile
up on top
Let’s Practice Together!

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Which rock layer is
the oldest?
Which rock layer is
the youngest?
Which is older,
layer M or layer R?
How do you know
Put them in order
from oldest to
youngest
Which is younger R
or T? How do you
know?
Think*Write*Pair*Share
Is dating rocks using the law of
superposition a form of relative dating or
absolute dating? Explain your answer
Remember…



Law of Superposition is a form of
relative dating
Relative dating is based on the rocks
that are surrounding it, NOT the
exact age
We know which is older but we do
not know HOW old exactly
TICKET
OUT!
1.
2.
3.
4.
Which rock is younger,
limestone or basalt?
How do you know?
Which of the labeled
rocks is oldest? How do
you know?
Which of the labeled
rocks is youngest? How
do you know?
Name the rocks in order
from oldest to
youngest.
Do Now
1.
2.
3.
What is the Law
of Superposition?
Which rock layer
is the OLDEST?
How do you
know?
Which rock layer
is the
YOUNGEST?
How do you know
Do Now
1.
2.
3.
What is the Law
of Superposition?
Which rock layer
is the OLDEST?
How do you
know?
Which rock layer
is the
YOUNGEST?
How do you know
D
R
A
O
T
C
I
K
N
G
Other Clues to
Relative Age
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Clues From
Igneous Rock
Lava that cools at
the surface is called
an extrusion. Rock
below an extrusion
is always older.
Magma that cools
beneath the surface
is called an
intrusion. An
intrusion is always
younger than the
rock layers around
Other Clues to Relative Age


Faults (a break in
the rock) are always
younger than the
rock it cuts through!
Unconformities: An
unconformity is a
gap in the geological
record that can
occur when erosion
wears away rock
layers and other rock
layers form on top of
the eroded surface.
Fossils



Fossils are usually
found in
sedimentary rocks.
When an organism
dies, its soft parts
often decay quickly
leaving only the
hard parts to
fossilize.
Ex. Bones, Shells,
Teeth, or Seeds
Using Fossils to Date Rocks!



Scientists use index
fossils to match rock
layers.
An index fossil must
be widely distributed
and represent a type
of organism that
existed only briefly.
They are useful
because they tell the
relative ages of the
rock layers they are
found in.
HOT Q 2
Which layer is
oldest? How do
you know?
Which layer is
the youngest?
Explain your
answer in at least
2 sentences.
(write) Geological Time Scale Review

Earth formed 4.6 bya (billion years ago)

Precambrian=no plants or animals yet– mainly
prokaryotes in ocean.
Paleozoic Era= Animals/plants develop. Fish in
the ocean and fern forests on land. Extinction at
end.
Mesozoic Era= Dinosaurs rule! Birds, mammals
appear. Extinction at the end.
Cenozoic Era= Age of mammals. This is our era!

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Most eras ended with a mass extinction (most
species died)!!
Fossils give us clues about. . .
 How
old a rock is.
 What life existed in the past.
 When big events happened.
 Climate in the past.
FOSSILS HELP FIND ROCK AGES
 Geologists can use fossils to
estimate the age of the rock around
it.
This is called RELATIVE DATING.
Relative Dating means finding the
age of an object in relation to other
objects.
INDEX FOSSILS (write)


Fossils used to help date rock are
called INDEX FOSSILS.
GOOD INDEX FOSSILS
ARE:


Found around the world
Around a short time
Index Fossils (write)


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Organisms that lived
during a specific time
IDENTIFY THE AGE OF
ROCK THEY ARE
FOUND IN
INDEX FOSSILS MUST
BE WIDE SPREAD
They also help compare
ages of rocks layers
around the world
Fossils and Climate (write)

Climate=average
conditions like
temperature, humidity,
wind, and rainfall.

Fossils show us how
climate changes over
time.
Ice Cores (write)

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Ice forms layers similar
to that of rock
Also follow law of
superposition
Contain elements that
help describe climate of
Earth
Scientists drill down and
pull ice cores up
An ice core from
Antarctica 3km long
showed 740,000 years
of history and 8 ice
ages!!!
Set Up Your Notes First!
(write)

What is an igneous
inclusion?

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What is an ice
core?
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Definition
2 Facts
Picture
Definition
2 Facts
Picture
Set Up Your Notes First!
(write)

What is an index
fossil?

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
What is an
unconformity?



Definition
2 Facts
Picture
Definition
2 Facts
Picture
EOG PRACTICE
Which statement BEST explains why
Greenland, which is ice-covered and located in
the Arctic region, has fossils of tropical plants?

a.
b.
c.
d.
Greenland was once located in the tropics and had
a tropical climate.
Birds carried plant seeds from the tropics to
Greenland.
Plants used to be adapted to grow in ice-covered
regions.
Ocean currents carried the fossils to Greenland.
Reading about Earth’s History

You are now going to read an article called
“Dating the Earth: Rocks, Fossils, and Ice
Cores”



This tells you key points the EOG always ask
its 8th graders
As you read you will be required to take
notes cornel style
This information will be on your
independent practice as well as the
assessment….SO DO A GOOD JOB!