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USGS CMG InfoBank: Paleomagnetism

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Comment: 23:26 - 24:38 (01:12)
Source: Annenberg/CPB Resources - Earth Revealed - 3. Earth's Interior
Keywords: "Scott Bogue", magnetism, "rock coring", "lava flow", "Mojave Desert", paleomagnetism

Our transcription: Many rocks contain a record of the strength and direction of the Earth's magnetic field that existed when the rocks were formed.
Here in the Mojave Desert of California, Geologist Scott Bogue drills for cores of lava which are keys to our magnetic past.
Lava flows of differing ages preserve evidence of a number of previous magnetic reversals.
They are like tape recordings of prehistoric magnetic behavior.
The study of these ancient magnetic fields is called paleomagnetism.
We can say something about ancient magnetic fields of the Earth because of the record they leave in rocks.
Many rocks become magnetized when they are formed or some time after they are formed.
When they become magnetized, they become magnetized parallel to the Earth's magnetic field at that time; so if you can collect a rock sample and measure which way it's magnetized and determine when it was magnetized, then you can learn about the orientation of the magnetic field at that time in the past.

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