When we think about life out there in the Universe, far beyond the limits of Earth, we can't help but look to our own planet as a guide. Earth has a number of features that we think are extremely important — perhaps even essential — for enabling life to arise and thrive. For generations, humans have dreamed of life beyond Earth, striving to find another world similar to our own but with its own unique success story: our own Earth 2.0.
But just because life succeeded here on Earth doesn't necessarily mean that life is likely to succeed on Earth-like worlds, only that it's possible. Similarly, just because life hasn't been found on non-Earth-like worlds doesn't mean that it isn't possible. In fact, it's quite possible that the most common forms of life in the galaxy are very different from terrestrial life forms, and occur more frequently on worlds different than our own. The only way to know is to look, and that necessitates looking for observational signals that might cause us to rethink our place in the Universe.