The formulation of theories which are mature hypotheses having stood the test of time, and which unify a variety of observations. The establishment of scientific laws and principles which are generalizations that explain some phenomenon for which there is no known deviation. Some material forms a fattened disk. Planets begin to accrete from the material in the flattened disk which is orbiting the sun, due to gravitational effects. Planetary separation Inner rocky planets are high density and small in size, the gases having been swept away by the solar wind.
Outer planets are low density and large in size with a large gaseous component.
Earth's interior is characterized by gradual increases in temperature, pressure and density. Heat continually flows outward into space. The temperature and pressure greatly affect the mechanical behavior or strength of earth materials. Plate tectonics - a recent theory in the Geological Sciences describing the dynamic processes. Plates move relative to one another as they slide over the asthenosphere through a combination of gravitational forces and thermal convection in the mantle.