Describe plate boundaries

Supplied materials

• All measurements and observations below are supplied classroom examples. They are not data from actual learners or a claim about a particular real site.
• Paper or a browser document for a labeled drawing, table or explanation.
• Worked problem inputs: Ocean-floor ages increase away from a ridge on both sides. Explain a mechanism fitting the pattern.
• Assessment case 1: Two plates move apart at a ridge where new crust forms. Predict the pattern as time passes. Which inference or prediction is best supported?
• Assessment case 2: Which scientific label fits the specifically described step or feature? Supplied case: Arrows point toward shared boundary.
• Assessment case 3: Which scientific label fits the specifically described step or feature? Supplied case: Parallel arrows pass in opposite directions.
• Assessment case 4: Which scientific label fits the specifically described step or feature? Supplied case: Site lies in middle of one plate.
• Assessment case 5: Which scientific label fits the specifically described step or feature? Supplied case: Spreading ridge separates plates.
• Assessment case 6: An oceanic plate approaches a trench and bends beneath another plate in the model. What follows? Which inference or prediction is best supported?

Learn the idea

Tectonic plates are moving pieces of lithosphere. Divergent boundaries separate, convergent boundaries approach and transform boundaries slide past. Actual boundaries have varied geometry and behavior.

Divergent means plates move apart. Convergent means plates move toward one another. Transform means plates slide past one another. Interior means location away from a depicted boundary.

For the supplied mechanism problem, Ocean-floor ages increase away from a ridge on both sides. Explain a mechanism fitting the pattern. New crust forms near the spreading region while plates move apart. Older crust is carried farther away over time. The pattern supports spreading when combined with other evidence.

1. Read the supplied problem and mark the structures, processes or quantities named: Ocean-floor ages increase away from a ridge on both sides. Explain a mechanism fitting the pattern.
2. Draw the relevant boundary, pathway or comparison and label it using the scientific ideas above.
3. Write a causal explanation or calculation, showing how each observation supports the result.
4. Compare your reasoning with the worked solution; name a condition that would change or limit the inference.

Check your reasoning

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Take it further

New task: draw plates separating at a ridge and approaching at a trench. Expected: divergence at the ridge and convergence at the trench; arrows must follow the relative movement rather than the picture’s left-right orientation.

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