Alternative Pathways in Astrobiology: Reviewing and Synthesizing Contingency and Non-Biomolecular Origins of Terrestrial and Extraterrestrial Life
The pursuit of understanding the origins of life (OoL) on and off Earth and the search for extraterrestrial life (ET) are central aspects of astrobiology.
Despite the considerable efforts in both areas, more novel and multifaceted approaches are needed to address these profound questions with greater detail and with certainty. The complexity of the chemical milieu within ancient geological environments presents a diverse landscape where biomolecules and non-biomolecules interact.
This interaction could lead to life as we know it, dominated by biomolecules, or to alternative forms of life where non-biomolecules could play a pivotal role. Such alternative forms of life could be found beyond Earth, i.e., on exoplanets and the moons of Jupiter and Saturn.
Challenging the notion that all life, including ET life, must use the same building blocks as life on Earth, the concept of contingency—when expanded beyond its macroevolution interpretation—suggests that non-biomolecules may have played essential roles at the OoL.
Here, we review the possible role of contingency and non-biomolecules at the OoL and synthesize a conceptual model formally linking contingency with non-biomolecular OoL theories.
This model emphasizes the significance of considering the role of non-biomolecules both at the OoL on Earth or beyond, as well as their potential as agnostic biosignatures indicative of ET Life. — Life
The model discussed here allows us to speculate about the initial formation of life as we know it (such as terrestrial life), or, life as we don’t know it, i.e., ET life. An arbitrary spectrum between non-life and life spans the diagram, indicating the transition and varying characteristics from abiotic to biotic forms. The starting point of life is arbitrarily termed the Last Universal Common Ancestor (LUCA) for simplicity. (Panel A) shows a deterministic origin of life (OoL) view, assuming a direct link between abiotic chemical space and biochemistry towards LUCA and, by extension, life as we know it on Earth. (Panel B) presents a contingency view, illustrating the numerous alternative paths that could have led to the OoL on Earth or on other planetary bodies, where a different type of “LUCA” could have appeared, representing life as we don’t know it. Below, we provide a legend detailing what each aspect of the model signifies. — Life
Alternative Pathways in Astrobiology: Reviewing and Synthesizing Contingency and Non-Biomolecular Origins of Terrestrial and Extraterrestrial Life, Life, Kuhan Chandru, Christian Potiszil, Tony Z. Jia (open access)
Astrobiology
