> Life began in that alien environment, and at some point between 3.2 and 2.8 billion years ago, cyanobacteria began to use sunlight to split hydrogen from water, discarding oxygen as waste.
Think this is wrong. The discarded oxygen during photosynthesis comes only from splitting CO2.
"In general, photosynthesis in cyanobacteria uses water as an electron donor and produces oxygen as a byproduct, though some may also use hydrogen sulfide[77] a process which occurs among other photosynthetic bacteria such as the purple sulfur bacteria."
Think this is wrong. The discarded oxygen during photosynthesis comes only from splitting CO2.