b) Earth's magnetic orientation is locked into rocks when the rock cools
Explanation:
The rocks are excellent, if not the best evidence of the changes that have occurred in the Earth's magnetic field. The reason for this is that the rocks that have metallic elements have the property to align their crystals toward the magnetic field of Earth, as the metallic elements react the easiest to the magnetic field and orientate themselves towards it. It has been noticed in the rocks of the past that not all of them have the same alignment of crystals, but some have their crystals aligned toward north, while some have their crystals aligned toward south. These rocks are also from different periods, and it is providing evidence that the magnetic field of Earth has actually been switching from the North to the South Pole and vice versa over our planets history.
