I recently read in a news article that there is a planet out there that has the same type of atmosphere and has all the necessary things that an organism needs to survive. It is called Gliese 581g, or Planet G. Scientists say that is is basically like a replica of Earth, only bigger! One interesting fact about Planet G is that it has one main season, that of summer. One pro about Planet G is that it is of good weather for the ecosystems, which means that we would have a way to produce food (planting food), but one con about Planet G is that it doesn't have days or nights as Earth does, but has just days... So it would always be light out. It is extremely cool that there might actually be a planet that is similar to Earth, and scientists also say that it is something they call a "Goldilocks planet", because it has everything necessary for human or bacetrial life. But the main question is... Could there be other forms of life that we don't know about? Planet G may have all the necessary items needed to have organism growth and may be thought to have other forms of life, but I feel that if we had other forms of life, we would be able to find out whether we did or we didn't... But it seems to be that even with the technology that we have today, we haven't gotten around to finding out whether there is such a concept as "aliens". I also believe that although a planet such as this one may have all the necessary features to handle life on it, but it doesn't necessarily mean that the planet, in this case Planet G, will have life on it.  I believe that no other forms of life exist in the world, even though evidence may point to there being life in some other planet that obtains the same requirements for life.

CITATION: http://news.discovery.com/space/earth-like-planet-life.html