Does the Amazon Rainforest Really Produce 20 Percent of the World's Oxygen?

SL_Photography/iStock via Getty Images
SL_Photography/iStock via Getty Images

Richard Muller:

No. In fact, under normal conditions (prior to human-caused fires) the Amazon [rain]forest is in a steady state. 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.

Except for the biomass decrease from human-caused fires, the biomass of the Amazon has not been changing. That means that no net carbon dioxide is being removed from the atmosphere, so no net oxygen is being released from carbon dioxide.

Recently the Amazon biomass has been changing due to fires. When that happens, the wood and other carbohydrates in the trees combine with oxygen and produce CO2 and H2O. Thus the burning of the rainforests contributes to global warming.

But under normal situations, when the biomass of the Amazon is not changing, there is no net production of oxygen or carbon dioxide.

Incidentally, many writers who don’t understand this—and mistakenly think that the Amazon produces net oxygen—double their error by using a backward metaphor. They refer to the Amazon basin the "lungs of the world," but lungs are the organ that remove oxygen from the air and replace it with carbon dioxide, not the other way around.

Where did the 20 percent figure come from? The best guess is that ecologists have calculated that 20 percent of the photosynthesis of the world takes place in the Amazon basin. But so does 20 percent of the consumption.

This post originally appeared on Quora. Click here to view.

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Why Did Noon Used to Mean 3 p.m.?

3 p.m. is basically noon for people who wake up at 12 p.m.
3 p.m. is basically noon for people who wake up at 12 p.m.
Mckyartstudio/iStock via Getty Images

If you’re a late sleeper, you might find yourself thinking 12 p.m. seems way too early to be considered midday, and the word noon would much better describe, say, 3 p.m. It turns out that ancient Romans would have agreed with you, if only for etymological reasons.

As Reader’s Digest explains, the days in ancient Rome were split into four periods of three hours each. The first hour was at sunrise around 6 a.m.—called prime, for first—followed by 9 a.m. (terce, denoting the third hour), 12 p.m. (sext, for sixth), and 3 p.m. (none, for ninth).

According to Merriam-Webster, Middle and Old English borrowed the time-keeping tradition, along with the Latin word for ninth, which was changed to nōn and eventually noon. Though we’re not sure exactly when or why noon started referring to 12 p.m. instead of 3 p.m., it could have something to do with Christian prayer traditions. In the Bible, Jesus’s crucifixion is said to have taken place at the ninth hour, and that’s when worshippers partook in their second of three daily prayers; the others were in the morning and evening. It’s possible that hungry monks were behind noon’s gradual shift from 3 p.m. to 12 p.m.—since their daily fast didn’t end until after the midday prayer, they had a built-in motive for moving it earlier.

While we didn’t exactly stay true to the original Latin meaning of noon, there’s another important remnant of ancient Rome hiding in the way we tell time today. Romans referred to 12 p.m. as meridiem, for midday, and so do we. A.M. is an abbreviation for ante meridiem, or before midday, and P.M. means post meridiem, or after midday.

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