can someone explain magnetic anomalies and reversals?

Question

How does this contribute to our current acceptance of plate tectonic theory

Answer 1

The earth is essentially a big ball of molten iron. Iron is magnetic. because it is molten it moves with convection, as the center of the earth is very hot, and the outer crust is cooler.

it is this movement of the magma (the molten iron) that moves the continents on top of it, and in turn generates the earth's magnetic field.

Magnetic anomolies are usually caused by large solid iron deposits that have a fixed magnetic field that close up is stronger than of the earth's, and of course is in a different direction.

No one understand why the earth's magnetic field reverses from time to time, but it does. Every 50milion years or so I think. I beleive the convection currents revers themselves but i'm not so sure. Bits of iron in new rocks formed in the center of the oceans are polarized to the direction of the earth's magnetic field at the time, and scientists have been able to read this information like a big cassette ape stretching back a few million years, so they are certain the reversals happen.

For reason's not fully understood,

Answer 2

General things can be said about the process. Convection does not reverse. The dynamo effect from a given convection pattern of molten iron in the core can amplify and support either polarity equally well. However, a mixture of positive and negative polarity is unstable and, if a reversal develops locally, it can grow until the whole earth reverses. I don't know if anyone knows how the local reversals get triggered. Perhaps it's a random upwelling of iron or something.