GRE Reading Comprehension
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Source: BOOST
The Earth's magnetic field is generated as the molten iron of the Earth's outer core revolves around its solid inner core. When surges in the molten iron occur, magnetic tempests are created. At the Earth's surface, these tempests can be detected by changes in the strength of the Earth's magnetic field. For reasons not fully understood, the field itself reverses periodically every million years or so. During the past million years, for instance, the magnetic north pole has migrated between the Antarctic and the Arctic.
Clearly, geophysicists who seek to explain and forecast changes in the field must understand what happens in the outer core. Unlike meteorologists, however, they cannot rely on observations made in their own lifetimes. Whereas atmospheric storms arise in a matter of hours and last for days, magnetic tempests develop over decades and persist for centuries. Fortunately scientists have been recording changes in the Earth's magnetic field for more than 300 years.
The passage suggests which of the following about surges in the Earth's Outer core?
- A They occur cyclically every few decades.
- B They can be predicted by changes in the Earth's inner core.
- C They are detected through indirect means.
- D They are linked to disturbances in the Earth's atmosphere.
- E They last for periods of about 1 million years.