Use crust ages to test plate-motion explanations

What pattern would seafloor spreading leave in crust ages?

Submit: An evidence record, explanation and revision.

Related lesson: Plate Tectonics and Earth History

This is a teacher-led extension beyond the short lesson. The task supplies a performance opportunity; completion alone does not certify mastery, full NGSS coverage or state alignment.

Build the idea

New oceanic crust forms at spreading centers and generally becomes older away from them. Subduction recycles oceanic lithosphere, helping explain why preserved oceanic crust is generally much younger than the oldest continental material. Real maps contain interrupted patterns, varied spreading rates and complex boundaries; a neat classroom transect is a model.

Evidence and model inputs

Invented symmetric transect: distance from ridge in km −200, −100, 0, 100, 200; crust age in million years 10, 5, 0, 5, 10. Compare this idealization with the actual ocean-age pattern in the USGS tectonic map. Continental evidence includes very old preserved regions rather than a global ridge-centered age pattern.

Keep actual observations, published findings and invented model cases labeled separately. If a source or required equipment is unavailable, pause that part with a teacher; do not invent results.

Materials and preparation

Paper, graph paper or spreadsheet, and the linked readings.

Grade-level scope

Use crust-age evidence; do not present an invented transect as a real ocean survey.

Do the work

1. Graph model age versus distance and calculate one side’s average spreading rate.
2. Inspect the USGS map and locate a real ridge with younger nearby crust and older crust farther away.
3. Contrast the model with map complexity and continental age patterns.
4. Construct an argument that compares seafloor spreading/recycling with a static-ocean-floor explanation.
5. Identify an additional line of evidence, such as earthquake distribution or magnetic patterns, that could test the argument.

Learner worksheet

Write on paper or type here and print. Entries stay in this page’s memory and are lost when you leave or reload; they are not saved or submitted.

Check your reasoning

1. What is the modeled one-side rate?
2. Is full separation rate the same as one-side rate?
3. Does one simple transect reproduce every ocean?
4. Why compare continental material?

Teacher review guide

Review the actual deliverable and discuss the reasoning. For each criterion, use 0 when evidence is absent or fundamentally incorrect, 1 when partly supported with a material error or omission, and 2 when accurate, supported and complete for the stated task. Maximum 8 points is a task score, not a proficiency certification. Give feedback and allow revision.

1. Analyzes age-distance patterns and rate units.
2. Uses an actual map in addition to the model.
3. Connects oceanic and continental age evidence to tectonics.
4. Evaluates a competing explanation and map limits.

Sources and standard reference

• Official NGSS HS-ESS1-5 performance expectation — inspect the practice, core idea, crosscutting concept and assessment boundary.
• USGS dynamic planet map background

Instructional text and hypothetical cases are original. Linked source readings supply published evidence where specified. Teachers should judge fit with their course and state requirements.