Why do paleomagnetic stripes appear on the seafloor?
Quick Answer
Paleomagnetic stripes form because lava at mid-ocean ridges records Earth’s magnetic field as it cools, and the field has reversed many times. New stripes are created symmetrically as seafloor spreads outward.
The Full Story
At mid-ocean ridges, molten rock rises from the mantle and cools into basalt. Tiny magnetic minerals in the lava align with Earth’s magnetic field while the rock is still hot and mobile. Since Earth’s magnetic field has switched polarity many times, newly formed crust can record either normal or reversed magnetism. As the seafloor spreads, these alternating magnetic bands appear as mirror-image stripes on both sides of the ridge. Their discovery in the 1950s and 1960s was key evidence for seafloor spreading and plate tectonics.
Key Facts
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"Why does the ocean floor look like a barcode?"