<span>The main difference is between the four outer gas giant planets and the four inner terrestrial planets. The four gas giants; Jupiter, Saturn, Uranus, and Neptune; are composed of hydrogen and helium. It is believed that they have solid iron-based cores. The terrestrial planets; Mercury, Venus, Earth, and Mars; are smaller and are closer to the sun. They have cores, mantles, and crusts; with a relative paucity of hydrogen and helium. The Earth differs from the other terrestrial planets in that it contains abundant ice and water, along with a nitrogen and oxygen atmosphere. Venus has a much thicker atmosphere of sulfur dioxide. Mercury has no atmosphere while Mars has a very thin atmosphere.</span>
Fossils are remains or traces of former life and not evolution. They are mainly formed from preserved hard parts of an organism but occasionally soft parts are also preserved. Fossils are normally found in sedimentary rocks.
