1. Grand Canyon Cross Section Tutorial

2. The Situation
Local gossip says there’s gold around the Grand Canyon at a latitude of 36 degrees 17’ and a longitude of 112 degrees 50’. Eager to get rich quick, a team of hopeful geologists, Raheem, Hank, and Bev plan to go looking around this area for gold. The layers they are interested in exploring are found under the line A-A’. The geologists are only interested in rocks that go as deep as the river. The two stars represent their core samples.
But first, there’s some information you will need to know.

3. Background: What do these geologists do?
Geologists are interested in the structure of layers of rock under Earth’s surface.
Geologists use representations called geologic maps to illustrate what rock layers are exposed at the surface of the earth.
They also use representations called topographic maps, and these are often combined into one map.
Intro

4. Background: The Geologic Map
A geologic map is a special-purpose map made to show geological features. Different types of rock are shown by different color to indicate where they are exposed at the surface.
Intro

5. Background: The Topographic Map
This type of map shows the elevation of an area of land.
The elevation is represented
by contour lines. The numbers
along these lines indicate the
elevation at a certain point on
the map. These numbers are
referred to as the contour interval.
What is the contour
interval for the map on the right?
Answer: This map has a
contour interval of 10.

6. Part 1: Make A Cross-Section
Raheem, Hank and Bev have to sketch a cross section to be able to record where the observations made, make predictions, and create and evaluate hypotheses.
Why might they want to record their observations?
What predictions might they make?
Why hypotheses might they make?
A cross-section is a drawing that shows what the inside of something looks like after a cut has been made across it.
Imagine slicing into a layer cake so that you can see the inside.
The inside is the cross-section.
Take our own pictures?
It might be beneficial to explore possible differences in understanding of what a prediction is and what a hypothesis is. If you want to include this topic add the following question after what hypothesis might they make?:
“Is there a difference between a prediction and a hypothesis?”

7. Part 2: Core Sample Comparison
Our geologists take core samples to see the way rocks are layered under the surface.
They use a special drill that fills a steel tube with rock is used.
The cylinder of material that they remove, called the core sample, is analyzed.

8. Part 3: Play-Doh Model
Models help us better understand and interact with the world around us.
With more data our geologists could model where the gold was found to know where they have and have not looked and to show other geologists a 3D version of the area using the data they collected by making cross sections, collecting core samples, and marking up maps.
Models have weaknesses but are still useful, especially when paired with other data. The model pictured here only has three layers, where the real Grand Canyon map has more, but the exposed layers are represented well despite this weakness.
How many layers of rock are on the map?
Change three layers depending on how many layers you would like.
Answer: The geologic and topographic map of the Grand Canyon has 8 layers.

9. Part 4: Why are these layers flat?
The Principle of Original Horizontality is a foundational theory in the science of geology.
Does anyone know this law or have they heard of it? What does it explain?
Answer: The Law of Original Horizontality states that the rock layers we see today were originally deposited horizontally and any deformation must have occurred at a later point in the rock forming process.

10. Raheem’s cross-section
Hank’s cross-section
These will also allow us to explore common misconceptions during the lab to provide better feedback for everyone.
Raheem didn’t realize how far across the cross section went;
Hank included his thought of where gold is located;
Bev got it mostly right, but her proportions are a not correct.
Bev’s cross-section

11. Raheem’s revised cross-section
Bev’s revised cross-section
Raheem’s revised cross-section
These will also allow us to explore common misconceptions during the lab to provide better feedback for everyone.

12. Hank, Raheem, and Bev’s play-doh model
Again, these will allow us to explore common misconceptions during the lab to provide better feedback for everyone.

13. Correct sketch of view from above

14. How is gold made in the Earth?
Help understand other interesting topics in geology to develop more inherent interest in the field.
Solution from deep in the Earth is forced up into the bedrock near volcanic activity (bottom left – see yellow space pushing through layers of crust this shows the processes that leads to gold formations). The liquid/water evaporates or leaves the vein and gold is deposited there to be found by humans much later in time (darker yellow connected to lighter yellow but wider is the deposit).

15. Start with spheres
2 inch diameter

16. Then make Cubes
3 x 3 x 0.5

17. Stack the layers

18. Cut the layers in half

19. Cut a “V” shape into the model

20. Disclaimer
There is no gold in the Grand Canyon! Thank you for your thoughtful responses. Have fun!