The question of life — what it is, how it can be recognized, and where its limits lie — stands at the very core of astrobiology, often defined as the study of the origin, evolution, distribution, and future of life in the universe. However, this definition already contains a fundamental difficulty: to search for life beyond Earth, we must assume that we know what life is, and this assumption is inevitably rooted in our terrestrial experience.

Most astrobiological research focuses on approaches that are shaped by an implicit assumption: that life elsewhere resembles, at least at a fundamental level, life as we know it on Earth. The similarities we observe among life forms on Earth are not necessarily universal features of life as such, but rather the result of a shared evolutionary history on our planet. If our tools, models, and expectations are calibrated to terrestrial biology, radically different forms of life may remain invisible — not because they do not exist, but because they fall outside our conceptual framework.

The similarities we observe among life forms on Earth are not necessarily universal features of life as such. 

Astrobiology thus finds itself in a tension: it must define life to detect it, yet every definition risks being too restrictive. This is not only a technical problem, but also a philosophical one, concerning the limits of knowledge and the conditions under which something can be recognized as living.

Rather than considering life as a property of isolated organisms, we should explore the possibility that it emerges from networks of interaction among organisms, environments, and planetary processes. To begin rethinking life beyond an individualistic and Earth-centered perspective, it is useful to return to the origins of life on our planet. In this context, the work of the American scientist Lynn Margulis represents a crucial shift, as it places microorganisms — rather than complex organisms — at the centre of planetary transformation.

Margulis showed that the earliest forms of life on Earth were microbial and that these organisms were not passive inhabitants of a given environment, but active agents in transforming planetary conditions. A significant example is the role of cyanobacteria in the oxygenation of the atmosphere: through photosynthesis, they gradually altered its chemical composition, making the emergence of more complex life forms possible.

From this perspective, life does not merely adapt to an environment, but co-constructs it. 

From this perspective, life does not merely adapt to an environment, but co-constructs it. The Earth’s atmosphere, often considered a background condition, is in fact the result of biological activity, and the boundary between organism and environment becomes less defined. This challenges a static and localized conception of life, suggesting instead that it operates across multiple scales and through distributed processes.

Margulis is …