In this hypothesis, life is believed to have begun at the sites of warm submarine springs where chemical energy was focused and the mixing of spring water with seawater could lead to the precipitation of chemicals. The precipitation of chemicals on mixing of solutions can form a barrier preventing further mixing and precipitation. This barrier can also provide a template for the assembly of chains of organic molecules, and act as a catalyst for electrochemical reactions.
This hypothetical precipitate, again operating in a naturally occurring biotic soup, consisted mainly of small groups of iron and sulfur atoms. Iron-sulfur groups still play an essential electrochemical catalytic role in all living cells. As a boundary, the precipitate concentrated organic molecules such as amino acids. These formed at depth below the spring where water and its dissolved chemicals reacted with rocks containing Fe and iron-rich minerals. The boundary also concentrated other chemicals that could participate in chemical reactions. As a catalyst the groups of FeSiO4 and Fe3O4 could activate molecular hydrogen (and probably methane which consists of carbon and hydrogen) which also formed at depth in the spring.
The hydrogen is essential for the synthesis of organic molecules. Electrons produced as a by-product (and representing the dissipation of energy) are transferred to a type of iron, known as ferric iron, dissolved in seawater. (The ferric iron is produced from dissolved ferrous iron (richer in electrons) at the ocean's surface by sunlight. The same processes cause the reddening of the surface of Mars as iron-bearing minerals have “rusted”.
As a template, the iron sulfide precipitate (consisting of small crystals of only a hundred atoms or so), could bond chemically to, and assemble a sequence of, the molecular components of RNA. Acid springs of high temperature, coupled to emergent magma plumes, emit ferrous iron and other transition metals to the ocean. Solar energy oxidizes some iron to the ferric state, generating a dispersed positive terminal. Cooler alkaline waters emanate from the deep ocean floor, bearing hydrogen, methane, ammonia, formaldehyde, cyanide and hydrosulfide - molecules reduced from water and carbon oxides by reaction with ferrous silicate, residual nickeliferous iron and ferrous sulfide. Where these waters seep into the ocean, mounds, comprising layers of ferrous sulfide and green rust flocculants and films, arise.
These mounds are where the reduced molecules are filtered and adsorbed. Concentrated, they react to form glyceraldehyde, amino acids, and the components of nucleosides. The fluids are prevented from mixing thoroughly with the surrounding ocean by the spontaneous precipitation of a barrier of colloidal iron compounds. Nucleotides can then assemble in green rust. The thermal potential begins to be dissipated but the chemical potential is dammed. Though the hydrothermal solution is constrained, electrons escape from adsorbed hydrogen through the conducting layers of iron monosulfide, drawn to reduce the photolytic ferric iron.
There is invasion of the iron sulfide/hydroxide barrier by protons, pyrophosphate and carbonic acid, through iron sulfide-walled micro-channels. The newly formed nucleotides poison the iron sulfide but combine with peptides, producing pRNA. The side chains of particular amino acids register to fitting nucleotide triplet clefts. Keyed in, the amino acids are polymerized, through acid-base catalysis, to alpha chains by invading protons.
The resulting short protopeptides sequester ready-made iron sulfide clusters to form ferredoxins, ubiquitous proteins with the longest evolutionary pedigree. These take over the role of catalyst and electron transfer agent from the iron sulfides, promote further chemosynthesis and so support the electrochemical reactor from which they sprang. The principal problem with this hypothesis is the reliability of the invasion and precipitation scenario.
To wit, how effective is the sulfide barrier and the green rust substrate at providing a template for biological macromolecules? In addition, to be more plausible, the hypothesis must assume a fairly high concentration of chemical precursors. Especially since, unlike the evaporation-concentration element of Miller’s biotic soup hypothesis, there is no specific mechanism for concentrating these molecules into sufficiently close proximity for the electrochemical bonding to take place.
ouderdom onstaan leven ;
Leven op aarde veel eerder ontstaan dan gedacht'
zie ook ; ( zoek abiogenesis )
Overigens hoef je ook in dergelijke rapporten geen eenduidig antwoord te verwachten, want dat is er (nog) niet. Dat zal er voorlopig ook niet komen, dit probleem is van een orde van grootte waar een compleet vakgebied zich decennia op kan storten voordat het volledig begrepen wordt.