Earth's magnetic field rotates in irregular intervals. The terrifying part is, the time it takes to complete the rotation, the different intermediate magnetic poles cancel each other out, and we are left with a much smaller magnetic field overall. As low as 10% of what earth has today.

Astrum's channel on youtube has several pictures and complete analysis[1]. (I have downloaded the whole channel on my computer, that's the filename.)

[1] How The Earth Got Its Magnetic Field (And Why It Might Not Protect Us Much Longer)

As the sea floor plates that are being created in the mid ocean ridges cool the magnetic orientation is recorded in the alignment of particles in the newly frozen rock.

We can see alternating bands of polarity in the rock that show what the orientation was over geological time. The bands that spread outward from the ridges are separated by millions of years and provide a clear picture of sea floor spreading, and continental drift.