Alien life remains a profound mystery — scientists can’t predict its form, composition or biochemistry. However, two fundamental principles likely apply to all life, no matter how exotic: it must harness and convert energy to survive, and it must possess some mechanism for reproduction. These universal requirements may be the only reliable criteria for defining life as no other alternatives are known yet. So how do we try to find something that is unknown?
When searching for detectable signs of life beyond Earth, people must work with reasonable assumptions. One critical hypothesis is that life rarely, if ever, exists in isolation. Instead, it almost certainly emerges within interconnected ecosystems where organisms compete for limited resources. This competition drives adaptation, specialization and ultimately, observable patterns in how life organizes itself within an environment.
The new article, published in ‘Nature communications’, introduces a novel and universal approach of detecting life beyond Earth by focusing on how biological systems organize resources along energy gradients. Unlike traditional biosignatures, which often rely on specific molecules like oxygen, methane or organic compounds, this method is agnostic, meaning it does not depend on Earth-centric biochemistry and could apply to life with fundamentally different chemistries.
The central argument is that life, as a thermodynamic disequilibrium system, inherently structures its environment to maximize energy extraction. This leads to observable stratification where resources are arranged in layers ordered by their energy potential. On Earth, this is evident in microbial mats, sediment layers or aquatic ecosystems where metabolically distinct organisms create structured chemical gradients (e.g., oxygenic photosynthesis at the top, sulfate reduction below and methanogenesis in deeper anoxic zones).
Abiotic processes can produce chemical gradients, but they typically lack the systematic, energy-ordered stratification seen in biological systems. Life, by contrast, actively maintains and optimizes these gradients for metabolic efficiency. The authors argue that detecting such structured, energy-dependent layering in planetary environments would strongly suggest biological activity, even if the underlying biochemistry is unknown.
This framework provides a more general and robust biosignature than molecule-specific approaches, reducing false positives from abiotic processes. It could guide future missions by prioritizing environments where energy-ordered stratification is likely, such as subsurface oceans or ancient hydrothermal deposits.
By shifting focus from specific chemicals to thermodynamic principles of life, this work advances the search for extraterrestrial life in diverse and unfamiliar environments. The energy-ordered stratification signature offers a universal criterion for life detection, independent of its underlying biochemistry.