The Priscoan Eon began about 4.6 billion years ago with the formation of the earth. Geological evidence shows that the earth's crust melted and hardened many times. Continents took shape and began to grow. Oceans and atmosphere also took shape in the early part of this eon. Most of the rocks that formed during this time were metamorphic. Many great masses of granite were formed. Life had not yet entered the atmosphere.