Solved cryptogram
A compass works because molten iron churning deep inside the Earth generates a magnetic field.
Earth Science Facts, sourced to U.S. Geological Survey.
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What it means
The outer core is liquid metal in constant motion, and moving conductive fluid generates electric currents, which in turn generate a magnetic field that sustains the motion. The field is not fixed. It wanders, weakens and strengthens, and the rock record shows that it has reversed its polarity hundreds of times, most recently a few hundred thousand years ago.
The claim comes from U.S. Geological Survey.
- SourceU.S. Geological Survey
- CollectionEarth Science Facts
- Difficultymedium
- Length79 letters, 20 unique
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