#80. The Restricted Weathering Theory of Abiogenesis

 CH   EV

Red, theory; black, fact

Last update: 08-21-2024

When the early Earth, which was initially molten, had cooled sufficiently to acquire a solid crust and allow liquid water to accumulate on the surface, the formation of the oceans presumably began.

Seawater forms from steam outgassing from volcanic vents, which simultaneously emit acid gasses such as hydrochloric acid. Therefore, the first rain would have been highly acidic. In the normal course of events, volcanic rain falls on surface rocks that contain sufficient alkalinity to completely neutralize the acid, contributing cations such as sodium in the process and producing salt water. However, I postulate that shortly after the formation of the Earth’s crust, the surface rocks were mostly encapsulated in carbonaceous pyrolysis residues, basically barbecue gunk, originating from carbon-bearing gasses in the atmosphere. How is the acid rain supposed to get to the rocks?

I postulate that sometimes it did, and sometimes it didn’t, leading to a scenario of nascent crust covered in interconnected puddles in which a broad range of pHs were simultaneously represented. At the connecting points, a pH gradient would have existed, which recalls the pH gradient across the mitochondrial membrane that powers ATP synthesis. 

More simply, a lump of lava coated in a capsule of pyrolysis residue and immersed in acid rainwater will have a proton gradient across the capsule with the correct direction to model the inner mitochondrial membrane with its enclosed matrix.

The carbon-bearing gasses in the atmosphere would have been methane and the result of methane combination with water (formaldehyde),  nitrogen (cyanide and cyanogen), and sulfur (DMSO, only plausible), all triggered by solar ultraviolet. This suggests that the pyrolysis residues will contain sulfur, oxygen, and nitrogen heteroatoms, as does coal. An imaginary pore through the capsule will be lined with such heteroatoms, which are candidates for playing the role of the arginine, lysine, aspartate, and glutamate residues in the ATP synthase catalytic site. Protonation-deprotonation reactions would be available for powering the formation of polyphosphate (a plausible ATP precursor) from orthophosphate. The conformational changes so important in the modern ATP synthase do not appear to be available in this primordial system, so we need to demonstrate the presence of an equivalent. Conceivably, the phosphorus-rich species diffuse up and down in the pore, producing proton transport as they do so that is linked to phosphate condensation reactions. Judging by the modern ATP synthase, coordination of phosphate to magnesium ions may also be part of the mechanism. Mafic rocks such as lava are rich in magnesium.

06-30-2024: The flux of acid through the pore will dissolve orthophosphate out of some minerals in the rock such as apatite. If we suppose that the pore is lined with carboxylic acid groups modelling glutamate and aspartate side chains, then at some depth in the pore the pH in the pH gradient will equal the pKa of the acid, and the acid groups will spend half their time protonated and half ionized, resulting in general acid-base catalysis in a narrow zone in the pore. Magnesium-complexed orthophosphate will be catalytically converted to an equilibrium mixture containing some pyrophosphate in this zone and then proceed to diffuse out the exterior opening of the pore before it can be converted back. As a result, the condensing agent pyrophosphate will be available in the early oceans for catalyzing the formation of organic macromolecules such as early proteins and nucleic acids, which are forerunners of important building blocks of modern life forms. 

The efficiency of the pyrophosphate synthesis would be enhanced by a high phosphate concentration, which would be due to the restricted, underfilm spaces in which the weathering processes were occurring.

08-21-2024: The gradual expansion of the underfilm weathered pockets eventually undermines the local pyrolysis film, causing a flake to detach. The remaining rock surface will be largely coated in the first organic polymers created by condensing agents at low temperature. The process then repeats, leading to successive generations of biofilm creation and detachment. At this point, an evolution-like biofilm selection process can be postulated.