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There is no agreed theory or ‘standard model’ for the origin of life on Earth. But I personally like the idea that life began in alkaline hydrothermal vents. These are geological features that can be found close to the spreading centres of the Earth’s tectonic plates, such as the Mid-Atlantic Ridge which runs along the floor of the Atlantic Ocean. Such vents are sources of molecular hydrogen, a side-product of a natural geological process called serpentinization. In one possible scenario, the hydrogen reacts with carbon dioxide dissolved in the ocean, catalysed by iron-nickel-sulphur minerals. This is the first step in a sequence which potentially can produce a huge assortment of chemicals, including many of biochemical significance such as amino acids.
There’s more. The vents form tall chimneys of calcium carbonate, structures with interconnecting pores of the order of a tenth of a millimetre. These could well have been the places where the chemicals became trapped and concentrated, allowing a trial-and-error biochemistry to develop. The path leading from a primitive metabolic cycle, to RNA, to the genetic code, to DNA and to primitive cellular structures is highly speculative but quite plausible.
If this scenario is right, LUCA (life’s last universal common ancestor) was born in virtual darkness deep beneath the surface of the sea.