If 100% of all photosynthesis stopped today, it would still take literally millions of years before animal life would even notice a change. It took hundreds of

If 100% of all photosynthesis stopped today, it would still take literally millions of years before animal life would even notice a change. It took hundreds of millions of years to build to roughly present levels, and very little oxygen is actually consumed. All the "easy" oxygen sinks (like iron turning to rust) are used up. Animals don't really use very much.