What constitutes evidence for life? It's a simple question with a not-so-simple answer. If we are to decipher the history of life on earth, or perhaps on another planet, we need to know how to recognize signs of life, however obvious or obscure. At USC, we use many techniques in concert to investigate biosignatures, from the examination of physical biosignatures (e.g., wrinkle structures in sandstones left behind by microbial mats), chemical biosignatures (isotopic and elemental signatures) and mineralogical biosignatures (minerals precipitated by microbes or as a result of microbial metabolism). Our investigations have broad reaching application to the study of life on Earth and form the basis of the search for life elsewhere.