 The Earth has a magnetic field that is driven by motions of fluid iron in the outer core. This magnetic field acts like a simple bar magnet, with motion lines traveling through the center of the Earth and wrapping around the Earth pointing back towards the North magnetic pole, as shown in this diagram. As we can see, if one is standing close to the equator, the field will be fairly flat, whereas if one is standing close to the pole, the field will be much more vertical. This direction is called the inclination. The magnetic field of the Earth is captured in sedimentary and igneous rocks at the time of their deposition and formation. That means geologists can capture these rocks or sample these rocks, take them to the lab, and measure the field when they were formed. If the field is flat, that means the rocks were formed closer to the equator, and if that inclination is closer to vertical, that means that the rocks were formed close to the poles. For the snowball Earth hypothesis, it is very, very interesting that many of the rocks that capture glaciation, that contain evidence of glaciation, were formed close to the equator with flat inclinations. And this is one of the major pieces of evidence that glaciers covered equatorial regions during the snowball Earth.