The discrepancies regarding the importance of rainforests for oxygen production is mostly due to confusing oxygen production with net oxygen surplus. The rainforest produces a huge amount of oxygen during photosynthesis. Some people have latched onto that number and claimed that these forests are important sources of oxygen. They forget that the forest plants and animals also USE oxygen for metabolism. The balance is close to zero-- forests are nearly oxygen-neutral, because the amount of oxygen generated in fixing a given amount of carbon is about the same as the amount of oxygen used to break down the carbon in metabolism. There will only be net oxygen production in habitats where carbon is permanently sequestered away from decomposers or chemical processes. The sea is like that. Plants in the ocean fix carbon, hence generating oxygen, but when the plants die, their carbon often sinks and ends up sequestered on the cold dark sea floor. So we get most of our oxygen from the sea. A quick internet search shows most sites giving the bogus "lungs of the earth" story. Beware of the internet!! Lou