Example 1
Ocean-floor ages are 1 million years near a ridge and 8 million years farther away. What pattern is supported?
Crust is younger near the ridge and older outward, consistent with seafloor spreading.
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Year 8
Evidence for plate tectonics
Recognise fossil, rock, ocean-floor, earthquake and satellite evidence for moving plates.
Method and worked examples
Matching fossils and rock sequences on separated continents support earlier connections when combined with other evidence. Ocean-floor rocks are generally youngest near spreading ridges and older farther away. Matching magnetic stripes on opposite ridge sides record changing field conditions as new crust forms and moves outward.
Earthquake and volcano belts mark many boundaries. Deep earthquake zones can trace descending slabs at subduction zones. Satellite positioning directly measures present plate motion. Several consistent evidence sources are stronger than one coastline resemblance. In an age table, compare distances from the same ridge: increasing age outward supports spreading, while details vary with spreading rate and geological history.
Example 1
Example 2
Why are matching fossils plus matching rock sequences stronger than a coastline resemblance alone?
They are independent geological observations that can be checked together against a past-connection model.
Watch out: Fossils, rocks, seafloor ages, magnetic stripes, earthquake depths and satellite measurements provide multiple evidence sources.