Scientists estimate that the Earth formed about 4.6 billion years ago. The Earth that we know today, the relatively peaceful home of myriad forms of life, didn’t appear overnight. Rather, it took billions of years to slowly evolve into its current form. The process of accretion that led to the formation of the Earth was a violent one, and it produced an Earth that was only a little less violent and hostile. For a few hundred million years, the early Earth was characterized by high temperatures, toxic gases, high levels of radiation, and ongoing high-impact collisions. Over time, these conditions improved and the Earth took on its distinctive structure with differentiated layers of core, mantle, crust, and atmosphere. This distinctive structure has important consequences: First, it helps explain why the surface of the Earth changes over time; and second, it helps explain why the Earth evolved into a suitable setting for living things.