The exosphere is the hottest layer of the atmosphere. The troposphere is Earth’s lowest atmosphere, covering about 55 percent of its surface. This air contains oxygen gas that helps keep living things alive and breathing. There are three types of gases in this layer: nitrogen, water vapor and trace amounts of carbon dioxide. The stratosphere is the next layer in our atmosphere that consists mainly of oxygen gas found around 18 kilometers (11 miles) above Earth’s surface and extends up into space as well.