Earth’s Magnetism

Gilbert’s Experiment In 1600 William Gilbert published a book entitled De Magnete wherein he explained the behavior of the magnetic rock. He proposed the earth itself was a huge spherical magnet with its poles situated almost at the geographic poles (what we call the north and south poles).

. Thus, he concluded that the earth is a MAGNET.

The commonly accepted theory is that the magnetic North and South Poles are created from either the spinning of Earth's core or the mantle (hot molten lava) under Earth's crust.  This means that the spinning magma is directly responsible for the position of the magnetic North and South Poles.

Magnetite are little pieces of iron ore found in rocks When molten rock solidifies, all the magnetite particles of any size line up in the magnetic field, pointing in the same direction. Therefore, the direction of the Earth’s magnetic field at the time is preserved in the rock. Geologists can detect which part of the rock is the north-seeking pole. In this way any piece of rock acts like a tiny magnet.

Magnetic pole reversal It has been found that the earths magnetic poles have reversed or flipped many times throughout Earth’s history.

HOW DID THEY KNOW THIS? Geologists found that there were bands of rocks that alternated in the direction that they pointed in. This was very puzzling, because there was no way that the rocks could have spun around. The conclusion was that the Earth’s magnetic field had changed every few million years. These patterns of strips of rocks with alternating magnetism are called magnetic striping

You tube video http://www.youtube.com/watch?v=x-p49IBuR1Y