The distinctive "fecal prints" of microbes potentially provide a record of how Earth and life have co-evolved over the past 3.5 billion years as the planet's temperature, oxygen levels, and greenhouse gases have changed. But, despite more than 60 years of study, it has proved difficult, until now, to "read" much of the information contained in this record. Research from McGill University and Israel's Weizmann Institute of Science, recently published in the Proceedings of the National Academy of Sciences (PNAS), sheds light on the mysterious digestive processes of microbes, opening the way towards a better understanding of how life and the planet have changed over time.