The oxygenation of the Earth’s surface, which occurred ca. 2.3 billion years ago, is the earliest unambiguous imprint of biology on a planetary scale. Therefore, the search for molecular oxygen features prominently in the prospective search for life on extrasolar planets. However, the connections between the evolution of life and the evolution of the oxygen content of the Earth’s atmosphere remain unclear. This talk will present emerging new perspectives on the Earth’s transition from an anaerobic to an aerobic world.