For at least two centuries most social thought has taken the earth to be the stable platform upon which dynamic social processes play out. Both climate change and the Anthropocene thesis – with their enfolding of dramatic geologic change into the space-time of social life – are now provoking social thinkers into closer engagement with earth science. After revisiting the decisive influence of the late 18th-century notion of geological formations on the idea of social formations, this introductory article turns to more recent and more explicit attempts to open up the categories of social thought to a deeper understanding of earth processes. This includes attempts to consider how social and political agency is both constrained and made possible by the forces of the earth itself. It also involves efforts to think beyond existing dependencies of social worlds upon particular geological strata and to imagine alternative ‘geosocial’ futures.