Sea Floor Spreading-Divergent Plate Boundaries

A Carolina Essentials^TM Activity

9-12

High School

Overview

This is a student modeling activity for divergent plate boundaries that illustrates the surface and internal processes occurring at divergent plate boundaries. The model is used for evidence to explain surface and ocean floor features at the Atlantic Ridge and the students are asked to extend the model to explain surface features of the Great African Rift Valley. The activity may be completed by small groups of students, pairs of students, or individually. The materials required even allow for the activity to be completed at home.

Phenomenon

What internal and surface geologic processes are at work here?

Essential Question

How do surface features provide evidence of Earth’s internal processes?

Activity Objectives

Construct a model of sea floor spreading.
Explain surface features in Iceland based on your sea floor spreading model.

Next Generation Science Standards* (NGSS)

PE HS-ESS2-1. Develop a model to illustrate how Earth’s internal and surface processes operate at different spatial and temporal scales to form continental and ocean-floor features.

SCIENCE & ENGINEERING PRACTICES

Developing and Using Models

DISCIPLINARY CORE IDEA

ESS2.A: Earth Materials and Systems

ESS2.B: Plate Tectonics and Large-Scale System Interactions

CROSSCUTTING CONCEPTS

Stability and Change

Materials

Sheet of card stock
Tissue paper
White printer paper
Ruler
Scissors
Transparent tape
2 pens, pencils, or markers(different colors)

Safety Procedures and Precautions

No PPE required. Remind students of proper use of scissors.

Teacher Preparation and Disposal

Copy or upload the student activity sheets. If time is a concern, you may wish to pre-cut the tissue paper, copy paper strips, and card stock. Models can be saved for additional classes or the materials can be recycled.

STUDENT PROCEDURES

1. Fold the paper in half lengthwise, twice. Unfold the paper and cut along the crease lines making 4-11 inch strips. Tape the 4 strips together making one- 44 inch strip.
2. Cut out a 4 inch square of tissue paper. In the center of the square, cut a slit the exact width of the strip of paper. Mark the ends of the slit with a half inch line.
3. Cut a 3 inch square from the center of the card stock.
4. Securely tape the tissue paper over the square in the card stock.
5. Fold the 44 inch strip of copy paper in half to make a double 22 inch piece. Do not crease the paper.
6. Insert the ends of the copy paper into the tissue paper slit until 1 inch of paper is above the slit. Hold the card stock up so the paper strip hangs freely. Sketch the model and label what each piece represents.
7. Slide the paper strip up 3 inches. Gently separate the strip into 2 pieces. Color the inside faces of the strips the same color.
8. Push the paper strip up an additional 3 inches. Select a second color and color the uncolored sections of the inside faces of the strips. Sketch and label the model.
9. Repeat steps 7 and 8 until the paper strip has been pulled through the slit in the tissue paper. Sketch the final model, paying close attention to any changes in the tissue paper.
10. Use the paper cover to block all the flashlight and repeat the observation.

TEACHER PREPARATION AND TIPS

If you are using individual components and not the kit, sort the components into a basket for students to ensure they have all the correct parts.

The slit in the tissue paper must provide a tight fit. The tissue should tear at both ends as the paper strip is pulled through, indicating an elongation of the fissure.

In lieu of sketching the model, students can take and upload pictures, then label the pictures.

Data and Observations

Model Development

Initial Model: Sketch and Label

This step models the initial upwelling of magma through a weak, thin section of the Earth’s crust.

Intermediate Model: Sketch and Label

The strip of paper now represents lava flow from the fissure outward. Old lava is being pushed away from the fissure as new eruptions take place.

Final Model: Sketch and Label

In the final model the paper strip should extend past the edges of the card stock base. This shows a complete cycle of magma upwelling and sea floor spreading at a divergent plate boundary and eventual recycling of rock with the return to magma at a convergent boundary. A convection current on both sides of the fissure is represented.

Analysis & Discussion

What does each type of paper represent in the model?

Copy paper strip = magma, card stock = crustal rock, tissue paper = thin, brittle crustal rock

2. The colored bands represent the Earth’s changes in magnetic field strength. How can this information be used as evidence for convection currents in the mantle?

When the magnetic bands match on opposite sides of a fissure that indicates the magma was from the same source but was pushed away from the fissure on both sides. The movement away from the fissure is an indication of a convection current.

3. Use the model you constructed for the Atlantic Ridge and apply it to explain differences and similarities between the rift valleys in Iceland and east Africa.

Both valleys are long, bounded by mountains on both sides. The valley floors are relatively flat with some evidence of lava flows. The Iceland rift valley must be younger as it is not as wide, and the rock cliffs do not show signs of much erosion. The valley walls are steep and jagged. The Great Rift Valley in Africa is much wider, and the mountain sides are smoother and vegetated indicating that the African Rift valley is older but had the same geologic origins as the Iceland Rift valley. Both features are evidence of a divergent plate boundary.