What caused the amount of oxygen in the atmosphere to stabilize to the extent that it is today?
a. oxygen was toxic to many of the organisms living at the time.
b. carbon dioxide dissolved into the oceans, eventually forming carbonate rocks.
c. carbon dioxide dissolved into the oceans and was eventually used in the formation of sea creatures' shells.
d. the amount of oxygen consumed by respiratory organisms balanced the amount of oxygen produced by plants undergoing photosynthesis.