A World War II submarine detector was later used to map magnetic stripes on the seafloor, helping scientists prove that Earth’s tectonic plates move

A device built to track enemy submarines during the Second World War went on to become one of the most important tools in Earth science. The fluxgate magnetometer, first developed to detect small disturbances in the planet's magnetic field caused by metal hulls beneath the ocean surface, was later adapted by scientists to study the seafloor itself.

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