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Life existed before photosynthesis. Taking electrons from H2S and oxidizing H2 coming out of hydrothermal vents. Photosynthesis allowed primitive cells to ventu

Life existed before photosynthesis. Taking electrons from H2S and oxidizing H2 coming out of hydrothermal vents. Photosynthesis allowed primitive cells to venture out of those vents and into the world. Therefore, it's hardly a surprise that "life finds a way" :)

mharig 2y ago
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adrian_b 2y ago
Life existed before photosynthesis. However there are only 2 known ways of obtaining energy for living without photosynthesis, which are called acetogenesis and methanogenesis. In both cases the inputs are free H2 and carbon dioxide (or alternatively carbon monoxide and water), while the output contains acetic acid for acetogenesis and methane for methanogenesis. Methanogenesis is confined to a certain group of archaea, while the simpler acetogenesis is widespread among bacteria and archaea and there is good evidence that the last common ancestor of all cellular living beings was able to do acetogenesis, using the free hydrogen provided by volcanic gases or hydrothermal vents. H2S can be used as a source of energy in 2 ways, both of which require photosynthesis. H2S can be used instead of water and oxidized by bacteria that are capable of anoxygenic photosynthesis, or it can be oxidized by using free oxygen that has been produced elsewhere by algae or plants, using solar energy (instead of free oxygen, other oxidizers may be used, for instance nitrate or sulfate, but those must have been produced elsewhere by using free oxygen, so ultimately also by using solar energy; sulfate can also be produced directly using solar energy, in anoxygenic photosynthesis). So H2S cannot be used to obtain energy in the absence of living beings that capture the solar light. (Because the reaction of H2S with CO2 does not produce energy, but it consumes energy.) Similarly, the living beings that oxidize H2 coming out of hydrothermal vents, using either oxygen or other oxidizers derived from oxygen or from anoxygenic photosynthesis, like nitrate or sulfate, are also completely dependent on the photosynthesis carried on by algae or plants elsewhere. Only the acetogenic and methanogenic bacteria and archaea are completely independent of solar energy and they depend only on the internal heat of the Earth as a source of energy (which is the ultimate cause of the production of H2 in volcanic gases and in hydrothermal vents, by the reaction of water with magmatic rocks that are chemically stable only at the temperatures from higher depths). Like other anaerobic bacteria, acetogens, methanogens, and also sulfate-reducing bacteria, are widespread in human guts, where all 3 groups consume the H2 produced by other bacteria in fermentations.

mharig 2y ago

[dead]

adrian_b 2y ago

Life existed before photosynthesis. However there are only 2 known ways of obtaining energy for living without photosynthesis, which are called acetogenesis and methanogenesis. In both cases the inputs are free H2 and carbon dioxide (or alternatively carbon monoxide and water), while the output contains acetic acid for acetogenesis and methane for methanogenesis. Methanogenesis is confined to a certain group of archaea, while the simpler acetogenesis is widespread among bacteria and archaea and there is good evidence that the last common ancestor of all cellular living beings was able to do acetogenesis, using the free hydrogen provided by volcanic gases or hydrothermal vents. H2S can be used as a source of energy in 2 ways, both of which require photosynthesis. H2S can be used instead of water and oxidized by bacteria that are capable of anoxygenic photosynthesis, or it can be oxidized by using free oxygen that has been produced elsewhere by algae or plants, using solar energy (instead of free oxygen, other oxidizers may be used, for instance nitrate or sulfate, but those must have been produced elsewhere by using free oxygen, so ultimately also by using solar energy; sulfate can also be produced directly using solar energy, in anoxygenic photosynthesis). So H2S cannot be used to obtain energy in the absence of living beings that capture the solar light. (Because the reaction of H2S with CO2 does not produce energy, but it consumes energy.) Similarly, the living beings that oxidize H2 coming out of hydrothermal vents, using either oxygen or other oxidizers derived from oxygen or from anoxygenic photosynthesis, like nitrate or sulfate, are also completely dependent on the photosynthesis carried on by algae or plants elsewhere. Only the acetogenic and methanogenic bacteria and archaea are completely independent of solar energy and they depend only on the internal heat of the Earth as a source of energy (which is the ultimate cause of the production of H2 in volcanic gases and in hydrothermal vents, by the reaction of water with magmatic rocks that are chemically stable only at the temperatures from higher depths). Like other anaerobic bacteria, acetogens, methanogens, and also sulfate-reducing bacteria, are widespread in human guts, where all 3 groups consume the H2 produced by other bacteria in fermentations.