Thought to arise due to the motion of molten iron in the earth's core, for 10 points, identify this thing which makes your compass point northward.
The Glatzmaier-Roberts model can be used to explain events that affect it, and VADM and VDM values are often used to study its behavior. Certain data sets from Columbia river basalt flows from the Steens Mountains notably show evidence for its erratic behavior. The South Atlantic Anomaly is the location where it has its lowest intensity and the Matuyama-Brunhes boundary about marks the last inversion of it, which occurred 800,000 years ago. It helps deflect solar wind, and causes Van Allen belts to stay together. Thought to arise due to the motion of molten iron in the earth's core, for 10 points, identify this thing which makes your compass point northward.
The Glatzmaier-Roberts model can be used to explain events that affect it, and VADM and VDM values are often used to study its behavior.
{magnetic field} of the earth [or {geomagnetic field}; accept obvious equivalents]