If there was a sudden drop in temperature after the evolution of the first living cells, the rate of fermentation would drop due to the temperature. My prediction would have to include the data, which is on the graph. The question does not include a temperature to base my hypothesis on so I would have to conclude that if the temperature suddenly dropped to 35ºC to -20ºC, that the initial cells would die, and that the atmosphere and the evolution of cyanobacteria would change drastically.