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Comment: 24:38 - 25:38 (01:00)
Source: Annenberg/CPB Resources - Earth Revealed - 3. Earth's Interior
Keywords: "Scott Bogue", magnetism, "magnetic reversal", "rock coring", "lava flow", "Mojave Desert", paleomagnetism
Our transcription: Scientists generally agree that the Earth's magnetic field reverses itself on the average of once every 500,000 years.
Widespread evidence suggests that the last reversal occurred 700,000 years ago, but there is also some evidence that as many as a dozen reversals may have occurred since that time.
We know that in general terms during a magnetic reversal, the field intensity decreases to 10 or 20 percent of its normal value, so at some point as the Earth were entering a reversal, there would be a decrease in field intensity.
We know by comparing the magnetic field strength today to measurements of the magnetic field 160 years ago that the Earth's magnetic field is currently decreasing in strength.
It's decreased about five percent since 1832, so some have claimed that the Earth's magnetic field may be entering a reversal right now.
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