  Even the most pessimistic analyses of the likelihood of life suggests life on Earth is not unique (Frank &amp; Sullivan 2016). Many scientists take that as a good reason to search for life elsewhere in the Universe. The current search for life elsewhere focuses on two extremes: the chemical byproducts of life and the technological signals of intelligent life. The social interactions of alien populations might be interesting, but they are hard to study as of yet. Thus, we search for biosignatures that might uniquely identify life from a great distance. We’ll take each in turn.