What effect did the increase in atmospheric oxygen by photosynthetic organisms have on earth in terms of the biosphere?

Increase in atmospheric oxygen by the photosynthetic organism to the biosphere evolved more complex forms of life. Many different plants, animals consuming plants, bacteria decomposing dead plants and animals evolved.These forms a food web in the biosphere. The remains of dead plants and animals release nutrients to the soil and ocean which are reabsorbed by the other growing plants.This food exchange  and energy exchange make the biosphere a self supporting and self regulating system .

hydrogen is a compound or a single element and a element is a pure substence that cannot be separated into simpler subtances

clorine is a compound its a chemical substance that forms when two or more different elements combine

so both hydrogen and clorine are compounds