The environmental problems and the climate issue point to the responsibility of human activities in the disturbances of the global ecosystem. It appears that Earth’s changes can no longer be set apart from those of society, as expressed by the notion of Anthopocene. Researchers in the natural and social sciences are now induced to work together on issues that have become shared. In this context I was asked as a sociologist to join an interdisciplinary team of researchers in Earth sciences, chemistry and engineering, to work on a project aiming to produce non-carbon hydrogen from waste of the iron and steel industry. This paper is based on fieldwork conducted as part of this project. Its purpose is to question what it is that natural sciences, in this case geology, are studying if we consider that an autonomous nature, independent of humans and of society, does not exist. Observation of geologists at work, mainly on their research field in the Alps, and the interviews I had with them, has led me to point out the intimate relationship that links them to the environment they are studying. This environment has little to do with some abstract natural world or with the global environment such as that of climate change for example. This definition of what is at stake in Earth sciences will impact on the understanding of environmental problems and on the collaboration between the natural and the social sciences that it implies nowadays.