Summary
Highlights
The Earth's magnetic field creates invisible lines of force that a compass senses. These lines emerge from the South Magnetic Pole and point towards the North Magnetic Pole. The Earth's magnetic field has reversed multiple times throughout history, known as magnetic reversals, where the poles flip, occurring every few million years.
Magnetic reversals are evidenced by ancient lava flows. When lava erupts and cools, tiny magnetic minerals within it align with the Earth's magnetic field at that specific time, essentially 'recording' the direction, whether normal or reversed. By examining layers of lava, scientists can observe a pattern of alternating normal and reversed magnetic polarities, demonstrating that the Earth's magnetic field has indeed flipped over geologic time.
The phenomenon of magnetic reversals is directly linked to seafloor spreading. At mid-ocean ridges, lava continuously erupts and solidifies. As new seafloor forms, it records the Earth's current magnetic polarity. When the magnetic field reverses, the newly formed seafloor records the opposite polarity. This process creates symmetrical stripes of rock with alternating magnetic polarities on both sides of the mid-ocean ridge.
The resulting pattern of symmetrical magnetic stripes found on mid-ocean ridges worldwide is undeniable evidence of seafloor spreading. This pattern is impossible to explain without both seafloor spreading and magnetic reversals occurring. Therefore, these magnetic patterns serve as strong proof that the seafloor is continuously spreading over geological time.