As you probably know, Earths atmosphere acts as as a blanket of gases that surrounds it. The atmosphere makes Earth very different from the moon or a planet that has no atmosphere such as Mars. If you have ever gazed up at the moon, one of the first things that you probably noticed was the massive craters covering it's surface. These craters mostly came to be because the moon has no atmosphere. When meteoroids move towards Earth, the atmosphere will usually cause it to burn up or explode. This way, It is less likely to cause major damage on Earths surface. Planets that do not have atmospheres cannot stop such damage from occurring. Another reason that Earth is not covered in craters is the factor of weather which is made possible by the atmosphere. When Lance Armstrong first set foot on the moon, he left a footprint there. Because the Moon has no atmosphere and therefore no weather, that footprint will remain on it's surface for a long time. In the rare occasion that a large crater is left on Earth, the weather will wash away. The atmosphere also provides us with oxygen which animals need to live so life as we know it on a planet with no atmosphere is simply not possible.