[M-IS20] 水惑星学

[MIS20-10] Liquid and supercritical CO₂ as an organic solvent in Hadean seafloor hydrothermal systems

*渋谷 岳造¹、高井 研¹ (1.海洋研究開発機構)

Prebiotic chemical evolution and the emergence of life in the seafloor hydrothermal systems of Hadean Earth is one of the most plausible and popular hypotheses for the origin of life on Earth. In contrast, many studies indicated that this hypothesis intrinsically harbors a critical unsolved problem called the “water paradox”: abundant water limits synthetic dehydration and facilitates hydrolysis of organic molecules during the early stage of chemical evolution. Nevertheless, many of these criticisms have not referred to the presence of abundant liquid/supercritical CO₂ (L/SC-CO₂) fluids and pools in modern hydrothermal systems. Indeed, the L/SC-CO₂ fluids and pools create dry environments and behave as hydrophobic solvents at and beneath the seafloor. In this work, we theorize the generation and preservation mechanisms of a L/SC-CO₂ pool in modern seafloor hydrothermal systems then reinterpret the fossil hydrothermal systems preserved in early Archean seafloor basalts. The theoretical consideration of subseafloor phase separation and phase segregation of CO₂-rich hydrothermal fluids points to the presence of L/SC-CO₂ fluids and pools also in Hadean seafloor hydrothermal systems. Because they behave as hydrophobic organic solvents, L/SC-CO₂ has the great potential to drive the dehydration synthesis of organic molecules in seafloor hydrothermal systems. Furthermore, at the interface between L/SC-CO₂ and H₂O-rich fluid (seawater or hydrothermal fluid), amphiphilic molecules might be generated and triggered into self-assembled growth. Based on the abundant occurrence and physico-chemical properties of L/SC-CO₂ fluids, we propose a new stepwise concept for the origin of life, whereby prebiotic chemical evolution was co-hosted and facilitated by L/SC-CO₂ in Hadean water-rich seafloor hydrothermal systems. This “liquid/supercritical CO₂ hypothesis” probably overcomes the water paradox and strengthens the idea that earthly life was hatched in deep-sea hydrothermal systems.