A century ago, scientists suggested that life is more than just a passenger on Earth. It benefits, they argued, from influencing the conditions on Earth, co-shaping its own habitat. This idea is now widely accepted, but our review shows we still lack a comprehensive theory of the biosphere’s role in the Earth system. Science-based Earth stewardship calls for collaboration of fields such as evolutionary theory, ecological thermodynamics, ecosystems modelling, biogeochemistry and land use science.