Earth may be the only planet in the solar system which supports life. There are a number of reasons which favours earth to support life starting from microorganism to humans, among the most important reasons are: Firstly, our earth has an atmosphere which has several important gases like oxygen, which is very important to support life. Secondly, a major portion of earth has a favourable climatic condition to support life. Thirdly, water is another most important elements to support life, the first life on Earth started in water. Fourth, without the sun there would be no earth, the sun is very important for the existence of life on earth. Fifth, another important thing is the presence of ozone layer on the atmosphere, though the sun is very important for life on Earth all the rays of the sun is not good, this ozone layer protects the earth from those harmful rays of the sun.