Search for signs of ancient microbial life in the geological record is challenging due to degradation of the primary organic material. Therefore, proof of biogenic origin often relies on chemical signatures that microorganisms leave behind. A new study of minerals in rock cracks presents chemical signatures that are definite proofs of widespread ancient life processes in the energy-poor continental crust. More importantly, the study greatly expands the known chemical variation of sulfur, one of the key elements in microbial metabolisms. This gives new clues to what type of chemical signatures to expect from life in extreme environments, including search for life on other planets.