Earth's Formation
Earth was formed 4.6 billion years ago during the period when our solar system was still very young. Collisions of smaller orbiting rocks and debris eventually combined to form a giant ball of molten lava (the heat was generated during the collisions), called Hadean (NATIONAL GEOGRAPHIC). When the conditions finally calmed down and the collisions stopped, the earth began to cool and form an outer crust of solid rock. The oldest rocks found on earth date to 3.9 billion years ago, but earth is always changing, which makes it difficult to pinpoint exact ages (EXTREME SCIENCE). The atmosphere of this time most likely consisted of primarily carbon dioxide, nitrogen, and water vapor, however was lacking oxygen. Approximately 3.8 billion years ago, the surface had cooled enough for the water vapor to condense and rain down to form huge oceans. These early oceans provided the ideal conditions in which many new complex molecules were synthesized, and the first life began (NATIONAL GEOGRAPHIC).