Mystery about "Radioactivity and the earth"

Most of the energy responsible for the geographical history of earth can be traced to the decay of the uranium,thorium and potassium isotope it contain. The earth is believed to have came into being perhaps 4.5 billion years ago as a cold aggregate of the smaller bodies that consisted largely of metallic iron and silicate material that had been circling the sun.

Heat of the radioactive origin accumulated in the interior of the infant earth and the time lead to partial melting.The influence of gravity then caused the iron to migrate inward to form the molten core of today's planet;the geomagnetic field comes from electric currents in the core.

The lighter silicates rose to form the rocky mantle around the core that makes up about 80 percent of the earth's volume.

Most of the earth radioactivity is now concentrated in upper mantle and the crust, where heat it produces escapes and cannot collect to remelt the earth.The steady stream of heat is more than enough to power the motion of the giant plates into which the earth's surface is divided and mountain building, earthquakes,and volcanoes associated with these motions.

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