Here's why:

* Seafloor Spreading: Mid-ocean ridges are where new oceanic crust is created. As magma rises from the Earth's mantle and cools, it becomes magnetized in the direction of the Earth's magnetic field at the time.

* Magnetic Reversals: The Earth's magnetic field flips periodically, meaning the north and south poles switch places. This leaves behind a record of magnetic reversals in the newly formed seafloor.

* Stripes: As the seafloor spreads away from the ridge, these magnetic reversals create a pattern of alternating magnetic stripes, with normal and reversed polarity. These stripes are symmetrical on either side of the ridge.

The discovery of magnetic striping provided crucial evidence for the theory of plate tectonics and seafloor spreading.