As the earth rotates, these electric currents produce a magnetic field that extends outward into space.
For example, in the process of making a fire pit, a person can use clay to create the desired shape of the firepit.
In order to harden the clay permanently, one must heat it above a certain temperature (the Curie point) for a specified amount of time.
On the earth's surface, when you hold a compass and the needle points to north, it is actually pointing to magnetic north, not geographic (true) north.
The Earth's magnetic north pole can change in orientation (from north to south and south to north), and has many times over the millions of years that this planet has existed.
Besides reviewing the basic principles of these methods, this article describes a number of applications, emphasizing explication of the method and solution of particular archaeological problems.