Alkaline fluid circulation in ultramafic rocks and formation of nucleotide constituents: a hypothesis

Abstract

Seawater is constantly circulating through oceanic basement as a low-temperature hydrothermal fluid (<150°C). In cases when ultramafic rocks are exposed to the fluids, for instance during the initial phase of subduction, ferromagnesian minerals are altered in contact with the water, leading to high pH and formation of secondary magnesium hydroxide, among other -brucite, that may scavenge borate and phosphate from seawater. The high pH may promote abiotic formation of pentoses, particularly ribose. Pentoses are stabilized by borate, since cyclic pentoses form a less reactive complex with borate. Analyses have shown that borate occupies the 2' and 3' positions of ribose, thus leaving the 5' position available for reactions like phosphorylation. The purine coding elements (adenine, in particular) of RNA may be formed in the same general hydrothermal environments of the seafloor.

Resolving the enigma of prebiotic COP bond formation: Prebiotic hydrothermal synthesis of important biological phosphate esters

“…We can also conclude that orthophosphate is one of the ultimate sources of P for the biological world. Also, for the synthesis of glycerol phosphates, condensing agents such as cyanamide or urea are not essential and hydrothermal conditions also favor the formation of C O P type biological compounds unlike the previous works, which show that the presence of Mg 2+ is somehow vital for the phosphorylation reactions [30]. We successfully synthesized the PO 4 compounds even without the presence of the former one.…”

Geochemical evidence for active tropical serpentinization in the Santa Elena Ophiolite, Costa Rica: An analog of a humid early Earth?

“…The presence of H 2 and CH 4 in the fluid controls the occurrence of biological activity, and methane and sulfur metabolizing microorganisms were found at the Lost City hydrothermal field, a peridotite-hosted hydrothermal system along the Mid-Atlantic Ridge [Schrenk et al, 2004;Kelley et al, 2005;Brazelton et al, 2006]. These systems are thought to be similar to those found in early Earth, leading to an increased interest in studying the ability of such environments to not only host the most primitive life-forms on Earth, but also to have served as a birth place of life [Russell et al, 1989[Russell et al, , 1994Fr€ uh-Green et al, 2004;Holm et al, 2006;Schulte et al, 2006;Martin and Russell, 2007]. Given their composition, other planets, planetesimals, or moons (such as Mars or Europa) hold the potential to host similar ecosystems [Russell et al, 1989;Hand et al, 2007;Russell and Kanik, 2010].…”

Os semimetais na origem e evolução da vida

“…34 A síntese laboratorial de RNA, simulando vias plausíveis do ponto de vista pré-biótico, não foi ainda alcançada, embora a síntese de ribose e de nucleobases tenha sido efetuada, 27 mas a dos ribonucleótidos é ainda repleta de dificuldades. Para além da síntese, constituem fatores difíceis de ultrapassar a baixa estabilidade da ribose e das nucleobases, a reduzida disponibilidade de fosfato 36 e a conjugação adequada destes componentes na síntese dos ribonucleótidos. 27,37,38 Também a síntese direta de ribonucleósidos de pirimidinas com uracilo ou citosina ainda não foi conseguida, embora uma versão ativada tenha sido obtida.…”