Final answer:
Basaltic magma rising into a mid-ocean ridge, which is an underwater rift created by divergent tectonic plates, forms symmetric magnetic stripes on the ocean floor.
Step-by-step explanation:
Alternating high- and low-magnetic-intensity bands mirrored on opposite sides of a ridge are created by basaltic magma rising into a mid-ocean ridge.
A mid-ocean ridge is an underwater mountain and rift system formed by an oceanic divergent plate boundary, where two tectonic plates are moving apart.
The Earth's mantle melts due to decompression, and the molten basaltic lava (mafic magma) rises through the rift to fill the gap between separating tectonic plates, solidifying to form new oceanic crust.
As it cools, the iron-rich minerals within the basalt align with Earth's magnetic field, which periodically reverses polarity. This process creates symmetric patterns of magnetic stripes on either side of the ridge, recording the history of our planet's geomagnetic reversals.