How do paleomagnetic stripes record seafloor spreading?
Quick Answer
As basalt cools at mid-ocean ridges, iron-rich minerals lock in Earth’s magnetic field direction. Because the field reverses over time, the ocean floor ends up with matching magnetic stripes on both sides of the ridge.
The Full Story
When lava erupts at a mid-ocean ridge and cools into basalt, tiny magnetic minerals align with the planet’s magnetic field. Once the rock solidifies, that magnetic direction is preserved like a tape recording. Over millions of years, Earth’s magnetic field has reversed many times, creating alternating bands of normal and reversed magnetism. These symmetrical stripes were key evidence, starting in the 1960s, for the theory of plate tectonics and seafloor spreading.
Key Facts
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"Why does the ocean floor have invisible barcode stripes?"