Rounded pillow lava on a fissured seafloor at the Galápagos Rift, photographed by a NOAA expedition.

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Preparing the 3D view

Preparing lighting and the first complete frame…

Model scale

Vertical dimensions ×12. ocean removed. magnetic colours symbolic.

Full spreading rate 25 mm/year · each flank 12.5 mm/year. Teal / sandstone: opposite remanent magnetic polarities.

How to read these results

Play advances an invented reversal record through 1 Ma. It illustrates symmetry, not the real geomagnetic chronology. Subsidence follows an illustrative √age curve; relief is not a bathymetric survey.

Seafloor spreading

Explain how new oceanic crust forms at a ridge and how magnetic stripes record spreading on either side.

Drag to rotate. Hold Ctrl and scroll to zoom, or pinch on a touch screen.

Why it happens

New oceanic crust forms at a spreading ridge and moves away on both sides. Its age generally increases with distance, while magnetic stripes record changes in Earth’s magnetic polarity.

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NOAA, Galápagos Rift, 21 July 2011. Lava quenched in seawater forms pillows close to a spreading centre, where new oceanic crust is built.

Try a comparison

Play the magnetic reversal sequence and follow paired markers. Compare wider and narrower stripes without assuming a constant reversal period.

Reading the result

The experiment uses a selected spreading history; real ridges change speed and can spread asymmetrically.

A common misunderstanding

Every magnetic stripe on the ocean floor represents the same amount of time.

Geomagnetic reversals occur at irregular intervals, and spreading rates can change. A stripe’s width depends on both the duration of its polarity interval and the rate at which crust moved away from the ridge. Matching sequences are stronger evidence than an assumption of equally spaced reversals.

Cases

Exam language

Spreading rate

The speed at which plates separate at a spreading ridge, usually expressed in centimetres per year. A full spreading rate measures separation across both sides; a half rate measures one side’s motion relative to the ridge, so the convention matters.

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NOAA EMAG2 v3 maps measured magnetic anomalies. Ocean-floor bands record crust formed under changing magnetic polarity. Matching the pattern to dated reversals supports seafloor spreading and allows a rate to be calculated from distance divided by age; colour alone does not give rock age.

Magnetic reversal

A change in the polarity of Earth’s magnetic field. Magnetic minerals in cooling volcanic rock can preserve the field’s direction at the time they formed. Reversals occur at irregular intervals, so magnetic bands do not all represent equal durations.

Mid-ocean ridge

A submarine mountain system at a spreading boundary, where mantle upwelling and melting form new oceanic crust. Seafloor generally becomes older away from the spreading axis.

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NOAA, Galápagos Rift, 21 July 2011. Lava quenched in seawater forms pillows close to a spreading centre, where new oceanic crust is built.

Vine–Matthews

The hypothesis linking symmetrical seafloor magnetic anomalies to spreading at ocean ridges and reversals of Earth’s magnetic field. Newly cooled crust records the field at formation. Comparing anomaly sequences with reversal ages provides evidence for plate movement.

Oceanic crust

The outer rocky layer beneath most ocean basins, composed mainly of basalt and gabbro and averaging about seven kilometres thick. It forms at spreading ridges and is eventually recycled at subduction zones. It is only part of an oceanic plate.

Magnetic stripe

A band of oceanic crust whose magnetic minerals record a particular field polarity. Seafloor spreading carries newly formed crust away from a ridge, producing broadly matching polarity sequences on its two sides. Stripe widths also depend on spreading rate.

Curie point

The temperature above which a material loses its spontaneous ferromagnetic or ferrimagnetic ordering; about 580 °C for pure magnetite.

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Magnetite, photographed in the Smithsonian collection. Pure magnetite loses its spontaneous magnetic ordering near 580 °C, its Curie temperature. This specimen photograph shows the mineral, not a temperature measurement.

Fracture zone

A long seafloor feature extending beyond a ridge-offset transform fault. Beyond the active transform segment, both sides move with the same plate.

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NOAA South Atlantic bathymetry. Colour represents seafloor depth, revealing continental margins, abyssal basins and the Mid-Atlantic Ridge.

Process0.40Full spreading rate25 mm/year