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How did magnetic stripes on the seafloor confirm seafloor spreading?

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Watch Earth's Continents Move — paleogeography Watch a time-lapse of Earth changing through geologic time, from the Cambrian Era to the projected period of Pangea Proxima.

Magnetic stripes on the seafloor provided critical evidence for seafloor spreading by acting as a chronological record of Earth’s magnetic field reversals.1

The theory, developed by Frederick J. Vine, Drummond H. Matthews, and Lawrence W. Morley, relies on three key assumptions: Earth’s magnetic field periodically reverses polarity, seafloor spreading occurs, and oceanic crust becomes permanently magnetized as it cools at spreading centers.1

As magma rises at a spreading center and cools, iron-titanium minerals lock in the orientation of the ambient magnetic field through thermoremanent magnetization. Because the crust is continuously split and pushed away from the ridge, it creates a symmetrical, parallel pattern of "stripes" on either side of the ridge axis. Positive anomalies represent crust formed during periods of normal polarity, while negative anomalies represent periods of reversed polarity.12

By matching these patterns to known time scales of magnetic reversals, scientists were able to date the oceanic crust and calculate the rate at which the seafloor spreads away from the ridge.13