Currently, the strongest argument that extraterrestrial life exists is as follows: (1) there are so many planets in the universe that some of them must have an environment similar to that of Earth; (2) in every environment on Earth that has been examined, life has been found; (3) the laws of nature are universal, so Earth-like planets should be able to support life as we know it in the same way that Earth itself does. With this line of reasoning, it seems all but certain that life must exist somewhere in the cosmos other than just here on our planet.