Complex sentence: Over time, bits and pieces broke off from Earth's core, their verticity having been corrupted and weakened by exposure to the degraded matter of Earth's crust, and became the variety of weak magnets found nearer the Earth's surface.
Split into simpler sentences: Over time, bits and pieces of matter escaped from Earth's core, their verticity having been corrupted and weakened by exposure to the degraded matter of Earth's crust. These bits of matter became the variety of weak magnets found nearer the Earth's surface.