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| Description: - Origin of Earth Most researchers believe that Earth and the other planets formed at essentially the same time - Nebular theory Solar system evolved from an enormous rotating cloud called the solar nebula Nebula was composed mostly of hydrogen and helium About 5 billion years ago the nebula began to contract Assumes a flat, disk shape with the protosun (pre-Sun) at the center Inner planets begin to form from metallic and rocky clumps Larger outer planets began forming from fragments with a high percentage of ices - Formation of Earth’s layered structure As Earth formed, the decay of radioactive elements and heat from high-velocity impacts caused the temperature to increase Iron and nickel began to melt and sink toward the center Lighter rocky components floated outward, toward the surface Gaseous material escaped from Earth’s interior to produce the primitive atmosphere Picture Stats: Views: 320 Filesize: 283.46kB Height: 921 Width: 981 Source: https://biology-forums.com/index.php?action=gallery;sa=view;id=39337 |