The Earth's magnetic field has another important property.
Like the Sun's magnetic field, the Earth's magnetic field "flips" or reverses polarity.
The amount of continental lithosphere has probably changed very little during the last 2.6 billion years (possibly increasing 10-15%).
What has changed, is the shape and the distribution of continents across the globe.
Because these magnetic anomalies form at the mid-ocean ridges, they tend to be long, linear features (hence the name "linear magnetic anomalies") that are symmetrically disposed about the ridges axes.
The past positions of the continents during the last 150 million years can be directly reconstructed by superimposing linear magnetic anomalies of the same age.
Wetness, or rainfall, also varies systematically from the equator to the pole.
It is wet near the equator, dry in the subtropics, wet in the temperate belts and dry near the poles.Fluctuations, or "anomalies", in the intensity of the magnetic field, occur at the boundaries between normally magnetized sea floor, and sea floor magnetized in the "reverse" direction.The age of these linear magnetic anomalies can be determined using fossil evidence and radiometric age determinations.In contrast to the continents and ocean basins, which are permanent geographic features, the height and location of mountain belts and the shape of the Earth's shorelines constantly change.Mountain belts either form where oceanic lithosphere is subducted beneath the margin of a continent, giving rise to a linear range of mountains, like the Andes mountains of western South America, or where continents collide forming, high mountains and broad plateaus like the Himalayan mountains and Tibetan Plateau of central Asia.Less extensive mountains can also form when continents rift apart (e.g.