How does the earth leave a permanent magnetic record on the ocean floor?

Sea floor striping is a fascinating subject.  As the sea floor spreads outward from the central zone, the rock rapidly cools and congeals, preserving a record of Earth's magnetic orientation within ferromagnetic particles (tiny bits of iron) entrapped in the rock.

Pole reversals are recorded in this rock.  I would not claim the record was permanent, however, in that along plate margins the sea floor is subducted into the mantle, where the record is destroyed.

The answer would be plant growth.