These experiments clearly suggest that biogenesis started in terrestrial hydrothermal vent environments, not in the submarine hydrothermal vent setting. In terrestrial setting, these vesicles can encapsulate nucleic acids such as RNA and DNA. Recent experiments suggest that these vesicles, precursors of protocells, are stable in hydrothermal hot spring water but are unable to assemble in seawater. Amphiphilic compounds, such as fatty acids, readily form membranous vesicles when dispersed in terrestrial aqueous phases. There has been growing evidence against the theory of submarine hydrothermal vent origins in recent years, which suggest that the lipid membranes and nucleotides could not have been formed in that environment during prebiotic synthesis. Geochemical reconstructions show that the ionic composition conducive to the origin of the cells could not have existed in marine settings but is rather compatible with emissions from vapor-dominated zones of inland geothermal systems such as hydrothermal ponds and crater lakes. Thus, protocells must have evolved in habitats with a high K +/Na + ratio and relatively high concentrations of Zn, Mn, and phosphorous compounds, as in terrestrial environments. The chemical nature of terrestrial hydrothermal vents resembles the cell's composition of its cytoplasm more closely than the open ocean environment. Recent work suggests that the chemistry of modern cells still mirrors the original environment in which life first evolved. Moreover, submarine hydrothermal vent environments lack wet and dry cycles, which are well known to promote polymerization of nucleic acids and proteins. In the open ocean, cosmic and terrestrial chemicals could never have mixed, concentrated, selected, or organized into more complex molecules. One crucial precondition for the origin of life is that comparatively simple biomolecules must have the opportunity to develop into more complex molecules through the segregation and concentration of chemical compounds. The cosmic ingredients would be dispersed and diluted, rather than necessarily concentrated, in the vastness of the global Eoarchean ocean, preventing them from assembling into the complex molecules of life. This theory suffers from the “dilution problem” of the precise organic compounds. The submarine vent hypotheses have considerable appeal but have not been universally accepted, partly because many aspects of the proposed scenarios remain unconstrained from geological evidence of the early Earth environment and chemical constituents of living cells. Submarine hydrothermal vents form in volcanically active areas-often on mid-ocean ridges. There are currently two competing hypotheses for the primordial sites-the crucibles-for the emergence of life: submarine hydrothermal vents and terrestrial hydrothermal crater lakes. Numerous island continents began to emerge amidst the vast global ocean. Ice is fairly common in the universe, but liquid water is rare. Water is the ideal solvent for life synthesis-dissolving many molecules, and transporting them to reaction sites, while preserving their integrity. Earth was no longer an alien inhospitable world, but was transforming into a life-supporting environment. Zircons are like tiny time capsules that retain the chemical fingerprints of a watery environment. Liquid water was prevalent as early as 4 billion years ago as revealed from the study of zircon crystals of that age. The cosmic liquid water began to accumulate on early Earth's surface to form a global ocean. Meteorites, especially carbonaceous chondrites, saturated with water molecules, delivered water, and carbon compounds during impacts. The Earth was still a one-plate planet before the inception of plate tectonics. Sankar Chatterjee, in Encyclopedia of Geology (Second Edition), 2021 Geologic Stageĭuring the beginning of the Archean Eon, about 4 billion years ago, as the frequency of meteorite impacts slowed, the Earth cooled, clouds formed, and the crust began to harden from the molten globe.
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