
If humans block out the sun, how come human can still breath outside the matrix?
We can understand that in zion, there could be a machine that produces their breathing air same as how it was describe their water was produced there. But outside the zion, where machines doesn't need to (except for matrix I guess), we can see humans can walk around breathing air as casually even without any apparatus.
Sunlight is very much essential for oxygen cycle on earth mostly for photosynthesis especially to marine organisms that produces more than half to 80% of it globally (sorry trees only produces small fractions of it).