7. What are the different stages …

When Earth formed 4.6 billion years ago from a hot mix of gases and solids, it had almost no atmosphere. The surface was molten. As Earth cooled, an atmosphere formed mainly from gases spewed from volcanoes. It included hydrogen sulfide, methane, and ten to 200 times as much carbon dioxide as today's atmosphere. The atmosphere can be divided into layers based on its temperature. These layers are the troposphere, the stratosphere, the mesosphere and the thermosphere. A further region, beginning about 500 km above the Earth's surface, is called the exosphere. Water vapor, carbon dioxide, methane, ammonia, and other gases similar to the ones produced by volcanoes today were expelled. Over a vast amount of time, millions of years, the earth gradually cooled. ... From these clouds, the oceans formed and the oceans absorbed a lot of the carbon dioxide in the atmosphere.