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I read an article where a physicist explains how the rainforest produces oxyden. Help me please understand the point of one passage:

Oxygen is produced by photosynthesis and consumed by decay. If these were out of balance, then the mass of wood in the Amazon must change. That means if the Amazon were to disappear today, instantly (e.g. we harvested all the wood and used it to build houses) then the oxygen and carbon dioxide in the atmosphere would continue on at the same level. Until, that is, the wood rots. Then the carbon dioxide levels would increase.

As I understand "until, that is" means while the Amazon exists (the wood rots), right?

Does "then" the last sentence means after the wood rots? why "would" is used? I'm not sure whether this sentence is a conditional.

Thank you

resource: http://mentalfloss.com/article/599602/does-amazon-rainforest-really-produce-20-percent-worlds-oxygen

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I think you are reading this correctly, but I'm not totally sure. "Until, that is, the wood rots" should be read as belonging to the previous sentence, describing how the oxygen/carbon dioxide levels would remain the same until the wood rots, within the imaginary scenario of the Amazon disappearing instantly. It is actually not a complete sentence... it is a sentence fragment, a phrase that technically should be connected to the last sentence. The author seems to have made it into its own sentence fragment for emphasis, creating a sense of urgency through the use of very short sentence fragments.

Here is a simplification of the end of the paragraph: "If the Amazon were to disappear today instantly, the oxygen/carbon dioxide would continue at the same level until the wood started to rot. Then, after the wood started to rot, the carbon dioxide would increase." I have emphasised the conditional words to show that this is all referring to the same imaginary scenario of the Amazon disappearing instantly.

If you notice, I used the past tense when saying "until the wood started to rot." It seemed more natural to me to use the past tense with the conditional verbs (I don't know the grammatical explanation for why!). The original author used the present tense, which doesn't sound bad, but I think the past tense usage would be more common. It seems like the author chose to use the present tense to give the impression that this imaginary scenario isn't too far from being possible. Again, it gives a sense of present urgency to the paragraph.

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    This answer is largely correct, except that I believe the first sentence wrongly identifies questioner's reading of the passage as already being in-line with your reading of it. The questioner interpreted it as "while the Amazon exists (the wood rots)", which, if I ignore the non-standard use of parentheses, suggests to me an incorrect reading of "While the Amazon exists, the wood rots." (Also, regarding your last paragraph, the author may have used present tense to emphasize the rot's delay. That is, the rotting would likely not have come about, yet.)
    – Jacob C.
    Nov 11, 2019 at 21:48

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