- Earth’s magnetic field generated by convection of liquid iron in the outer core (geodynamo)
- extends from the core through the mantle, crust, and out into space as the magnetosphere
- deflects solar wind and charged particles, protecting the atmosphere from erosion
- the magnetosphere channels particles to the poles, creating auroras
- enables navigation: compass alignment with magnetic north used for millennia
- magnetic poles wander and periodically reverse (last reversal ~780,000 years ago)
- paleomagnetism in rocks provided key evidence for plate tectonics and seafloor spreading
- shields surface life from cosmic radiation, a prerequisite for biological evolution
- field strength has decreased ~9% over the last 200 years
- the South Atlantic Anomaly is a region of weakened field affecting satellites
- connected to energy dynamics of the planetary interior through thermodynamics