Which of the following is the reason that tropical rain forests are called the Lungs of the Earth?The answer was:
They breathe out more than 20% or the Earth's oxygen.I had never heard that specific tidbit before and initially thought, "Oh, well, that's interesting." But then I thought about it a little more and quickly came to the conclusion that the answer was nonsensical. The first thing that struck me was the 20% figure. Twenty percent of what? Total oxygen in the atmosphere? That seems unlikely. Twenty percent of all oxygen consumed? Must be it, but that's not made clear by the answer.
But the "breathe" and "Earth's lung" concepts seem even more problematical to me. After the oxygen is breathed out, is it all breathed back in? If so, that's just another way of saying that twenty percent of the Earth's total metabolic processes occur in the tropical rain forests and that they are their own lungs, not lungs for the Earth.
The other choice is that the tropical rain forests breathe out and the oxygen is exported to the rest of the world. Indeed, that's what the answer to the question seems to imply. But where does this oxygen come from? I think the only plausible choice is that it's stripped from CO2. But if the rainforest is a net exporter or "O", then there's that pesky residual "C" left laying around in the forest. If the carbon isn't somehow also exported, it will start to pile up. I don't think much of the carbon is exported in any other form than CO2 (which requires "O" to produce). Therefore, if oxygen is exported, we would see a net increase, year after year, of carbon based compounds in the tropical rain forests.
I don't think that happens. Sure, when a tree grows it collects carbon. But when it dies, it rots and the carbon is converted back to CO2 by insects, fungi, micro-organisms, etc. The tree starts as nothing and ends as nothing. All of the tree, including it's leaves, seeds, etc., are ultimately consumed except for tiny fractions on average that may get buried. But I find it unlikely that those tiny fractions add up to anywhere near 20% of the earth's consumed oxygen.
I didn't (and still don't) know if my analysis was correct. So, I googled it. Many sites confirm the concept of the tropical forests being the earth's lungs. Here's one for example:
The Amazon Rainforest has been described as the "Lungs of our Planet" because it provides the essential environmental world service of continuously recycling carbon dioxide into oxygen. More than 20 percent of the world oxygen is produced in the Amazon Rainforest.However, numerous others agree with my analysis. Wikipedia, for example, states:
Tropical rain forests are also often called the "Earth's lungs", however there is no scientific basis for such a claim as tropical rainforests are known to be essentially oxygen neutral, with little or no net oxygen production.What do you think? Who's right? Is my child being fed bogus propaganda? Or scientific fact?