Relative Dating

Background

Looking at the cross-sections of rock formations, we can determine the relative ages of the layers and features in the formation. The study of strata is called stratigraphy. The table below lists five events that can occur in a rock forming environment:
Event Description Tectonic location / process
Sedimentation The Principle of Original Horizontality states sediments are laid down in horizontal layers. The Principle of Superposition explains that younger layers are above older. Subsidence due to tectonic processes or changes in sea level.
Erosion Gaps in the geologic record caused by erosion of rock are called unconformities. Results from uplift at convergence boundaries.
Deformation Layers of rock are folded and distorted. Usually caused by mountain building at convergence boundaries.
Intrusions Magma can cut across existing rock formations. Such a cross-cutting event must be younger than the formations it crosses. Results from hot spot magma intrusions or magma intrusions due to melting at convergence boundaries.
Faulting Another cross-cutting event. Found at most tectonic boundaries.

Part 1 - Tasks:

You will form teams of 2-3 people. Each team will invent a series of events that would create an interesting cross-section of rock.

Materials:

a. description / event sheet

Procedure:

  1. Agree upon a name for your team. This name must be used on all materials turned into the instructor.
  2. Record on the description / event sheet a list of events. You must include all five events listed in the table above. To make an interesting model you will likely have to use more than just five events. Include a sketch of what each event would do to the formation.
  3. Start with at least three sediment layers.
  4. Have the instructor review and sign-off your description / event list.

Deliverables:

Each person of the team will turn in a neat, legible description/event sheet for their team's model.

Part 2 - Tasks:

The team will make a model from baker's clay of their rock formation.

Materials:

a. Baker's clay c. wax paper e. Your completed description/event sheet
b. plastic knife d. clay form

Procedure:

  1. Use your event list to create a rock formation model. It is important to faithfully follow your event list.
  2. When finished with the model, write just your team name on the bottom of the model and store it as directed by the instructor. Do not write your team member names on the model.

Deliverables:

The team will turn in their baker's clay model.

Part 3 - Tasks:

The team will examine a rock formation model and try to determine the sequence of events that took place to create that formation.

Materials:

a. A rock formation model b. description / event sheet

Procedure:

  1. On scratch paper record the list of events (with a simple sketch) that created the model rock formation you are examining.
  2. When you are sure of the sequence of events, transfer your notes (with nice sketches) to a description / event sheet.
  3. Write your team name and the name of the team that created the rock formation you are examining on you paper.
  4. When finished return the model and your description / event sheet to the instructor.

Deliverables:

Each person of the team will turn in a neat, legible description / event sheet for the model.

Part 4 - Tasks:

You will comment on the other team's evaluation of your rock formation model.

Materials:

a. Your team's rock formation model
b. The other team's description/event sheet for your model.

Procedure:

  1. Get your rock formation model and the other team's description / event sheet
  2. Compare your description / event sheet with the evaluating team's description / event sheet.
  3. Note if their event list differs from yours. If so determine who is correct!
  4. Each team member will comment in their own words.

Deliverables:

Each person of the team will turn in their comments on the other team's evaluation.

Questions

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  2. and here
  3. and here
  4. and here

Relative Dating Description / Event Sheet

Your name Your team's name
Instructor sign-off Other team's name
Event Description Sketch