Chemotrophs probably existed before photosynthesis. The latter is a rather complex sequence of enzymes and took a while to evolve. Chemotrophs hijack natural r

Chemotrophs probably existed before photosynthesis. The latter is a rather complex sequence of enzymes and took a while to evolve. Chemotrophs hijack natural rock chemistry reactions. Most likely it was the weathering of fresh, hot basalt at underseas volcanos. Some of these metabolic pathways require no enzymes to proceed. Then enzymes would evolve to allow such life to expand into less opportunistic environments.