Dynamo theory

1946 Dynamo theory

The book of science

Tom Sharp

Walter M. Elsasser electromagnetism geophysics Dynamo theory

Dynamo theory

For Earth to maintain a magnetic field, convection must occur in its outer core. Earth’s outer core is a molten sphere that surrounds a more solid sphere, the inner core. The radius of the inner core is about 1,220 kilometers; the radius of the outer core is about 3,400 kilometers. The radius of the earth itself is about 3,959 kilometers, so the inner core is about 559 kilometers (347 miles) deep. Walter M. Elsasser said that convection and the Coriolis effect induce electric currents that result in the magnetic field.

Dynamo heat

The heat comes from many sources— gravity, compression of the core, separation of lighter from heavier elements, crystallization at the inner core boundary, and radioactivity of potassium, uranium and thorium. Plus, for moons of larger planets—tidal forces.

Dynamo power

A huge electric current drives a magnetic field, extending from the earth toward the sun ten times earth’s radius and away from the sun two hundred times, protecting our world from solar storms. It’s likely that if this were not so, then we wouldn’t be the creatures we are; we wouldn’t be dynamo-power people.

Our safety on this planet is fragile in the geologic time scale. Nations, languages, and species are more transient than it would seem. The strength of the magnetic field that protects our atmosphere from the solar wind has been decreasing by over six percent per century. Will high SPF sunscreen be sufficient during the next chaotic magnetic field reversal?

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