This question isn't defined; the Earth's
atmosphere is 20% oxygen. The mass of the Earth's
atmosphere is about 5 x 1018 kg, which
means 1018 kg of oxygen. The total
biomass of the Earth is thought to be about 5 x
1014 kg, most of which is plants.
This would mean that for every kilogram of
plant matter, there are about 5,000 kilograms of
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