It is known that the tilt of the earth's axis is 23.5 degrees, which accounts for the seasons on earth. The tilt causes certain parts of the planet to be heated differently thus causing seasonal changes. Of all the inner planets Earth is the only one that contains water in its liquid form. This is essential to the development of life on Ear th, as scientists believe. Since water was so important for life, scientist today use liquid water as one of the main references to finding life on other planets inside and out of this solar system.
Earth has an atmosphere made up of nitrogen, carbon dioxide, hydrogen, oxygen and water vapor.
Earth's atmosphere consists of four layers, the troposphere, Stratosphere, the mesosphere and the thermosphere. The ozone layer, which consists of three molecules of oxygen molecules bonded together. This layer helps to protect earth from dangerous radiation and reflects most of the radiation from entering earth. The ozone layer is approximately 10 miles up from the ground. Earth has an inner core of solid nickel and iron and a layer of liquid iron and nickel surrounds this core.