Major processes of the earth that create the structures comprising the planet are: Volcanism - volcanic activity - producing igneous rocks Gradation - weathering, erosion, deposition of material - producing sedimentary rocks Diastrophism - breaking, folding and bending of rocks - producing metamorphic rocks Volumes have been written about the Plate Tectonic Theory, but in a nutshell, it is described herein in its simplest terms. The illustration above shows one type of plate interaction, diverging plates. In this instance, the plates are being pushed apart by forces acting upon the plate and an intrusion of volcanic lava, or molten rocks. Since the plates "ride" on the plastic layer of the Mantle, the Asthenosphere provides a sliding surface for the plates to move upon. Where does the heat to melt this volume of rock originate? The heat source is from two primary sources. First, is the Primordial heat. Primordial heat is defined as "the energy left over from a planet's formation. It was generated when immeasurable numbers of planetesimals (comets and asteroids of all shapes and sizes) collided at hyper-velocities to build up the planet". And the other source of heat is from radioactive decay or Radiogenic heat. The earth has many radioactive materials in its constitution, such as U-235, U-238, Rb87, K40, etc. When these elements decay, they give off heat. Having enough volume of radioactive compounds along with the stored heat in a particular area will produce enough heat to melt rocks.

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