Relative Age with Edible Rocks Name: __________________
Activity
4th grade PSI Science
-----------------------------------------------Activity Question
How is relative age dating used when observing rock layers?
Before You Begin
How can we tell if one rock layer is older or younger than
another?
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What is the Principle of Superposition?
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Purpose
During this experiment, you will observe edible “rocks “ and their
layers to better understand relative age dating and the Principle of
Superposition. These edible “rocks” are a model of rock layers
like we find in nature. You will sketch pictures of the “rock” layers
and also think about the step-by-step process that led up to the
rocks formation. (Remember to answer Lab Questions during
class while you are engaged in the activity. Conclusion Questions
can be answered after class.)
Materials
 Bite size bars cut in half (2 halves per student)
Procedure
1. Sketch a cross-section of your “rocks”. (show details)
Rock 1
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Rock 2
4th Grade PSI Science
History of Planet Earth
2. Draw step-by-step pictures of how one of your “rocks” formed.
Rock # ___
1st
2nd
3rd
4th
3. Share your step-by-step drawing with a partner. Have them
share their model with you. Discuss any similarities or
differences you see in your drawings or in your thoughts about
how the rock formed.
4. Prepare your ideas about how the rock formed to share with
the class. You and your classmates will present ideas and vote
on the most likely process of formation.
Lab Questions
1. What is the oldest layer of these “rocks”? How do you know?
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2. What is the youngest layer of these “rocks”? How do you
know?
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3. From looking at your rocks, can you tell exactly how old the
rock layers are? (3 days, 2 years, 5 months?) Why or why
not.
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4. Using the step-by-step pictures you drew, explain how you
think that rock formed.
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4th Grade PSI Science
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Conclusion Questions
1. How are the edible rocks you examined similar to rocks
found in nature?
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2. How are they different?
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3. Relative dating is the process of using layers of rock to find
out if one layer of rock is older or younger than another layer
of rock. Did you use relative dating during this activity? How
does it relate to the Principle of Superposition?
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4th Grade PSI Science
History of Planet Earth
TEACHER NOTES
When picking bars to use for this activity, it is important to choose bars that have
multiple layers. Some ideas for candy bars to use are: Snickers, Kit-Kat, Milky Way,
and wafers. Snickers work very well and are one of the best candy bars to use if
possible. This is because of the layer of caramel and peanut inside, which simulates a
rock layers with fossils. Bars with just horizontal layers and no ingredients that model
fossils will challenge students thinking less, but can be used alongside another bar that
models this well.
It is a good idea to have all students sketch the formation process (step #2) for the
same candy bar so that ideas can be shared and compared.
This part of the activity, having students draw step-by-step pictures of how a rock
formed, can be a challenging question. Even though it might seem straightforward to
draw a step-by-step process of how the edible rock formed, it is usually difficult for the
students to grasp. Every student will have a different idea about how the rock formed,
however, based on the available evidence, only a few scenarios are possible. So in
short, you should look for students to:
Draw the oldest layer first.
Draw the next oldest layer second.
Draw the next oldest layer next. (If using Snickers bars, this layer can be
challenging since it contains peanuts inside of “sediment”, but allow students to
make their best hypothesis.)
Etc…
Remind students that laboratory questions should be answered while they are doing the
activity, not afterwards.
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Answer Key
Answers to the Lab Questions:
1. What is the oldest layer of these “rocks”? How do you know?
answers will vary depending on bars used
because it is the layer at the bottom of all the layers
2. What is the youngest layer of these “rocks”? How do you know?
answers will vary depending on bars used
because it is the layer on the top of all the layers
3. From looking at your rocks, can you tell exactly how old the rock layers are? (3
days, 2 years, 5 months?) Why or why not.
No, because you can only tell which layers are older or younger than each
other.
4. Using the step-by-step pictures you drew, explain how you think that rock formed.
answers will vary
Answers to the Conclusion Questions:
1. How are the edible rocks you examined similar to rocks found in nature?
The rocks have layers, contain particles in some layers, the layers are not
all made of the same thing, display the Principle of Superposition.
2. How are they different?
The layers are made of food not sediment, the layers have not cemented
together as strongly as a rock does, the rock has probably formed much
quicker than rocks in nature, it is easy to see the rock layers compared to
in nature where it is more difficult.
3. Relative dating is the process of using layers of rock to find out if one layer of
rock is older or younger than another layer of rock. Did you use relative dating
during this activity? How does it relate to the Principle of Superposition?
I did use relative dating during this activity.
Relative dating and the Principle of Superposition go hand in hand; the
Principle of Superposition can help you figure out a timeline of oldest to
youngest within rock layers, and relative dating looks at specific layers and
figures out their age in comparison to each other.
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4th Grade PSI Science
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