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Biology Help!?
which of the following led most directly to a decrease in the amount of ultraviolet radiation reaching the Earth's surface?
a.fermentation
b.anaerobic respiration
c.a reducing atmosphere
d.heterotrophs
e.photosynthesis
please explain your answer, thanks!
Photosynthesis. When blue-green algae emerged about 3 billion years ago, there was no appreciable free oxygen in the Earth's atmosphere. It was mostly bound in CO2, NO2 and various others compounds. The BGA started converting the CO2 into O2 and sugars, giving Earth its oxygen rich atmosphere.
Oxygen exists mainly as O2, but in the stratosphere, the ultaviolet light breaks these molecules up, and they recombine to form O3, or ozone, which absorbs UV.
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