Earth Magnetic Field
The liquid metal iron core of a planet creates a magnetic field. This field is not constant. From time to time it reverses, so that a compass points south instead of north. This happens every few million years. We are not sure whether this has any effect upon living things on Earth. Nor do we know when it will happen again, or what causes it.
The Earth's magnetism is very fortunate, since it protects life on Earth from dangerous particles in the solar wind. If planets did not have magnetic fields, life would be impossible.
One thing we do know is that the core of the Earth is still hot today, keeping the magnetic field in place and also driving continental drift.
The solar wind controlled by the Earth's magnetic field
