Download Magnetic Striping

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