What are strips of magnetic polarities found in rocks in ocean basins?

Strips of magnetic polarities found in rocks in ocean basins are known as magnetic anomalies. These anomalies occur due to the periodic reversal of Earth's magnetic field, which causes the newly formed oceanic crust at mid-ocean ridges to record the direction and intensity of the magnetic field at the time of solidification. As tectonic plates move apart, these alternating strips of normal and reversed magnetic polarity create a symmetrical pattern on either side of the ridge, providing evidence for seafloor spreading and plate tectonics.