Earth's early atmosphere is estimated to have had several hundred times as much CO2 as it does now, which would have dissolved in the ocean, and then you can ge

Earth's early atmosphere is estimated to have had several hundred times as much CO2 as it does now, which would have dissolved in the ocean, and then you can get a whole host of simple organic molecules - alchols, hydrocarbons, aldehydes and so on - via reactions catalyzed by volcanic particles. Space carbonic acid not required (and it forms from CO2 in water anyway). See for example Synthesis of prebiotic organics from CO2 by catalysis with meteoritic and volcanic particles (2023) https://pubmed.ncbi.nlm.nih.gov/37231067/ https://pubmed.ncbi.nlm.nih.gov/37231067/