For the past 25 years, Malcolm Walter has been the world’s foremost authority on stromatolites and a leading expert on the geological record of Earth’s earliest biosphere. He has gathered the geological evidence for the first microbial ecosystems in sediments and in hydrothermal environments, with spinoffs to models of ore genesis and the exploration of Mars. He has articulated the concepts that have directed research in these fields throughout the world. In detailing the succession of stromatolites, Walter studied Australian Neoproterozoic stratigraphy, leading to improved international correlation as well as an appreciation of petroleum prospectivity in rocks of that age.