Gravity as a Physical Selector of Chemical Evolution and the Origin of Life.

The origin of life signifies one of science's most profound mysteries, demanding integrative comprehension from chemistry, biology, and physics. In this review we examine the coupled roles of chemical evolution, biological evolution, gravity and light in shaping the earliest stages of life. We discuss how conditions established by the Big Bang, stellar nucleosynthesis and early planetary environments provided the energetic conditions necessary for the emergence of prebiotic chemistry. Going beyond the geocentric perspective, we explore extraterrestrial chemistry and analyze how gravitational fields and electromagnetic radiation jointly influence molecular stability, reaction kinetics, diffusion and spatial confinement. A central hypothesis advanced here is that planetary gravity constitutes a critical, but underappreciated physical selector in prebiotic evolution. Excessively strong gravity may suppress molecular mobility and dynamic self-organization whereas very weak gravity may prevent the retention, concentration, and stabilization of reactive intermediates. Earth's gravitational acceleration (∼9.81 m s⁻²) may therefore represent a "sweet spot" regime that optimally balances stability and dynamism. Using illustrative examples from prebiotic reaction networks, vesicle self-organization, osmolarity-driven processes, and early peptide-based catalysis, we discuss how gravity could have shaped the emergence of sustained metabolic networks, molecular surrogates, and protocellular systems. We further extend this framework to later evolutionary transitions, including the role of cytoskeletal elements in overcoming gravitational constraints during the colonization of land. Together, this interdisciplinary synopsis provides evidence for gravity's role as a continuous physical selector acting from chemical evolution to biological complexity, with implications for planetary habitability and the potential uniqueness of life on Earth.