Simply put, if there were no atmosphere, there would be no life on Earth! The atmosphere protects the surface from the intensity of the sun's radiation, because gases and aero
…sols (tiny suspended particles or droplets) intercept and absorb some of it. This is why the ozone layer (a part of the stratosphere that has a high level of ozone) is so important -- ozone, or O3, is particularly efficient at absorbing ultraviolet light. Another reason that the atmosphere is so important is that it keeps the temperature relatively constant at the surface. It may not seem like it sometimes, but the Earth's temperature is quite stable. Just how stable is apparent when compared to the moon. The moon has no atmosphere, and the temperature difference between areas in shade and areas illuminated by the sun is more than 250 degrees C (almost 500 degrees fahrenheit)!. That being said, an atmosphere does not guarantee life. Venus has an atmosphere, but it is extremely hot, thick, and carbon dioxide rich -- and did I mention the sulfuric acid clouds? (MORE) 
