The Earth's magnetic field varies depending on your location on the Earth's surface. In regions near the magnetic poles, such as Siberia, Canada, and Antarctica, it can exceed 60 microteslas (0.6 gauss), whereas in regions farther away, such as South America and South Africa, is around 30 microteslas (0.3 gauss). Near the poles, the field strength diminishes with the inverse square of the distance, whereas at greater distances, such as in outer space, it diminishes with the cube of the distance. Where the prime meridian intersects with the equator, the field strength is about 31 microteslas.
The region where the Earth's magnetic field lines extend into space is called the magnetosphere, and influences the trajectories of the charged solar wind at distances exceeding 10 Earth radii. Solar wind, ejected from the Sun in all directions at great speeds, collides with the magnetosphere in a region called the bow shock. Like gravity, magnetism has an infinite range, although it diminishes so quickly with distance that its power at ranges much beyond 10 Earth radii is very low.
30-60 microteslas for the magnetic field of the Earth may not sound like a lot, but when you take into account the total volume of the field, its total energy is extremely large, much larger than any magnetic field generated artificially. To get a better idea for what a tesla is, a typical bar magnet has a field strength of 10 milliteslas, a strong electromagnet 1 tesla, a strong lab magnet 10 teslas, and the surface of a neutron star, about 100 megateslas.
The Earth's magnetic field may not be so strong in comparison to localized magnetic fields, but it does effect minerals all over the surface of the Earth. When magma leaks out of cracks in the oceans and cools, the Earth's magnetic field orientation is reflected in the resulting structure of the cooled rock. By analyzing magma that hardened millions of years ago, scientists have found that this field flips every 250,000 years or so.
