10. Earth's
Magnetic Field
Expedition Menu
Modified from the CD-ROM ODP's From Mountains
to Monsoons
The great temperatures within the interior of the Earth produce movements in the liquid iron of the outer core. The movements, in combination with the very hot temperatures produce electrical currents -- unfortunately we do not have enough time to go into the evidence for this process in the detail - it deserves an entire expedition alone.
Anyway, Faraday long ago showed that electrical currents produce magnetic fields -- you cannot separate the two -- which is why it is often called electromagnetism.
Anyway, the Earth has a magnetic field -- which is why a compass needle puts north. The diagram (cartoon) at the left shows the lines of force of the Earth's magnetic field.
The Earth's magnetic field is quite complicated in detail, however, much of it can be approximated as if there was a bar magnet, with a positive (+) pole and a negative (-) pole, at the center of the Earth -- remember it is the electric currents in the outer core that produce the field -- but it mimics the lines of force associated with bar magnet, which many of you have played with in your childhood (and maybe still do on your refrigerator door).
The north pole of the Earth's magnetic field is near the Earth's geographic north pole, which is defined by the Earth's rotational axis -- but does NOT occupy the same, exact location -- but it is close.
Measurements of the Earth's magnetic field, especially information of the Earth's past magnetic field now locked in rocks beneath the seafloor, provided critical information in the development of the theory of plate tectonics -- we will learn more about this later in the expedition.
Created By:
Don Reed
Dept. of Geology
San Jose State University
©Copyright 2008
Last Updated on
Sept. 22, 2008
The Earth's magnetic field is produced by:
a) electrical currents in the outer core
b) electrical currents in the inner core
c) by a large bar magnet at the center of the Earth