Liquid and supercritical CO2 as an organic solvent in Hadean seafloor hydrothermal systems: implications for prebiotic chemical evolution

Abstract

Prebiotic chemical evolution and the emergence of life in the seafloor hydrothermal systems of Hadean Earth is among the most plausible and popular hypotheses for the origin of earthly life. In contrast, many studies pointed out that this hypothesis intrinsically harbors a critical unsolved problem called the “water paradox”: Abundant water limits dehydration synthesis and instead facilitates hydrolysis of organic molecules during the early stage of chemical evolution. However, many of these criticisms have not referred to the abundant liquid/supercritical CO2 (L/SC-CO2) fluids and pools in modern hydrothermal systems, which not only create dry environments but also behave as hydrophobic solvents at and beneath the seafloor. In this paper, we theorize the generation and preservation of a L/SC-CO2 pool in modern seafloor hydrothermal systems and reinterpret the fossil hydrothermal systems preserved in early Archean seafloor basalts. The theoretical estimation of subseafloor phase separation and phase segregation of CO2-rich hydrothermal fluids suggests the presence of L/SC-CO2 fluids and pools in Hadean seafloor hydrothermal systems. Because they behave as hydrophobic organic solvents, L/SC-CO2 can potentially initiate the dehydration synthesis of organic molecules in seafloor hydrothermal systems. Moreover, 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 physicochemical 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” potentially overcomes the water paradox and strengthens the idea that earthly life was hatched in deep-sea hydrothermal systems.

In Situ Measurement of Liquid and Gas CO2 with High Purity at Deep-Sea Hydrothermal Vents in the Mariana Arc Using Raman Spectroscopy

“…Another possible reason is that the diagram does not consider sodium chloride (NaCl) and other components in seawater. While the existence of NaCl and other components in seawater influences the conditions of the phase, , the condition of the phase transition for the seawater and CO 2 is not fully understood …”

“…While the existence of NaCl and other components in seawater influences the conditions of the phase, 44,45 the condition of the phase transition for the seawater and CO 2 is not fully understood. 20 The phase transition of CO 2 from liquid to gas was clearly observed in the CO 2 peaks in the Raman spectra. Figure 8 shows the wavenumbers of the two CO 2 bands assigned to the Fermi diad (ν 1 and 2ν 2 ) and their distances plotted against the depth.…”

“…However, the solvent and reaction properties in natural seawater and hydrothermal fluids have not been fully understood. 20 In the previous studies, the sampling of such hydrothermal gas and sc-/liq-CO 2 was attempted, while the contamination of hydrothermal fluids and seawater always occurred. The phase and compositional changes of the collected CO 2 emissions during the sampling and recovery were more or less unavoidable, even using any of the conventional fluid samplers.…”

“…Exploration of hydrothermal systems in the Mariana Arc and the Okinawa Trough found that spontaneous emissions of CO 2 , dominantly sc-/liq-CO 2 and sometimes gas CO 2 , are widespread in deep-sea hydrothermal fields, likely connected to large CO 2 sources beneath the seafloor in such regions. − The unique physicochemical nature of sc-/liq-CO 2 provides dry environments and hydrophobic/hydrophilic interfaces in seawater that play a potentially significant role in ocean geochemical cycles as a nonaquatic solvent for gas species, polymetallic nanoparticles, and organics. , In addition, it has been pointed out that the dry environment in hydrothermal sc-/liq-CO 2 in the early Earth might have contributed to prebiotic chemical evolution, which is key to the origin of life. , The behavior of sc-/liq-CO 2 as an organic solvent is similar to hydrocarbons, , and it is important to understand how the chemical compositions of hydrothermal sc-/liq-CO 2 and CO 2 -rich hydrothermal fluids change in response to the pressure and temperature conditions in oceans. However, the solvent and reaction properties in natural seawater and hydrothermal fluids have not been fully understood . In the previous studies, the sampling of such hydrothermal gas and sc-/liq-CO 2 was attempted, while the contamination of hydrothermal fluids and seawater always occurred.…”

A compositional view comparing modern biological condensates and primitive phase‐separated compartments

“…Protocells are the simplest compartments that likely existed on early Earth and formed abiotically; it has been proposed that modern cells evolved from protocells. [12,13] There are several different protocell models that perform various prebiotically relevant functions, including lipid or polymer vesicles, [14] polyelectrolyte microcapsules, [15] colloidosomes, [16] proteinosomes, [17,18] supercritical carbon dioxide, [19] and coacervates. [20][21][22] Among these, coacervates are generated from LLPS where a macromolecule-rich condensed liquid phase separates from the aqueous solution.…”