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17

A definitive statement comes from the abstract of Scott and Glasspool1, 2006: Charcoal, a proxy for fire, occurs in the fossil record from the Late Silurian (≈420 Myr) to the present. One of the tired old truisms you learn is that fire needs three things: Oxygen, fuel, and a source of ignition. There is little doubt that there has been lightning since ...


11

Both of them. The composition of the atmosphere, crust, mantle, core and bulk earth are all notably different. The atmosphere is composed of ~78% nitrogen and ~21% oxygen, with small amounts of other gases. The bulk composition of the earth by weight is mostly, iron, oxygen, silicon and magnesium, in that order, with all the other elements making up only ...


8

No, that will not happen. There is just too much oxygen in the atmosphere. Over 20% of our atmosphere is oxygen. Only about 0.04 % of our atmosphere is CO2, so too much CO2 would kill us much sooner than the lack of oxygen. If you reduced the oxygen concentration in the atmosphere from 20.8% to 19.8%, you wouldn't even feel the difference. If you reduced ...


8

I'm not sure I can give a good technical answer. I don't think the amount of oxygen in the Earth's atmosphere is due to equilibrium but more of a consequence of the formation of the solar system, Earth chemistry and biology. If you look at the formation, for inner planets, much of the gas and ices were blown off due to their inner orbits and the planets ...


8

I cannot find any language in peer-reviewed literature (as far as publicly accessible) that makes the 20% claim reported in the question. I therefore consider this claim to be of obscure and dubious origin. About 50% to 55% of the oxygen produced via photosynthesis is estimated to come from the world's oceans, as reported in the following two papers: ...


7

The Carboniferous was when the growth of woody plants took off. Non-plant life had not yet evolved the ability to consume lignins, the key chemical components that makes woody plants "woody". Lignins are rather hard to decompose. Despite high volcanic activity, carbon dioxide levels fell by a factor of over four during the Carboniferous, from over sixteen ...


7

Is it true that during the time of the dinosaurs, both the oxygen requirements (by all living creatures on the planet) and the CO2 released by volcanoes were higher than the same type of oxygen requirements today and the CO2 pollution created by us and the currently active volcanoes? I'm not quite sure what "Oxygen requirements" means. It seems to ...


7

Because Al and Si were already oxidised to begin with. When the Earth formed, it had some amount of metals (Fe, Si, Mg, Al, Ca, etc) and a fixed amount of oxygen to bond with those metals. Certain metals with bond with oxygen preferentially. Mg and Ca are usually the first to take up oxygen, followed by Al, Si, and then Fe comes last (out of the short list ...


6

Photosynthesis has not stopped. It happens all the time, splitting water and carbon dioxide, and producing oxygen and carbohydrates. Likewise, organic matter rots and decomposes all the time, requiring oxygen and releasing carbon dioxide. The Keeling curve actually illustrates this quite nicely: most of the land mass where this happens lies in the north, and ...


5

To complement @DavidHammen answer and address the point "where did so much oxygen come from?" I will elaborate on David's final remark The end result was a gradual increase in oxygen levels The short answers to "where did so much oxygen come from?" is: mostly from volcanos in the form of $\ce{CO2}$. To understand this, we have to consider that the ...


5

Do we need to worry about oxygen? No. Although some reports have claimed the Amazon produces 20% of the world’s oxygen, it is not clear where this figure originated. The true figure is likely to be no more than 6%, according to climate scientists such as Michael Mann and Jonathan Foley [Twitter links]. Even if it were accurate, the crops being planted in ...


5

First, let me clarify this again: Al2O3 is not clay. Now, back to topic. You are mixing apples and oranges here. The geological section you are referring it was deposited 2 billion years after the GOE. This was long after all surface iron was oxidised, and abundant oxygen was present in Earth's atmosphere. Nowhere you will see the (oxidized) Ferrum in ...


4

Atmospheric oxygen is not in an equilibrium of 21%, it just changes very slowly. For instance, oxygen has decreased by 0.7% over the past 800 thousand years, likely due to increased erosion (which exposes more rock that can be oxidized) and cooler oceans (which can then absorb more oxygen). So, while it is a slow process on geologic timescales, the amount ...


4

If I understand it right, you are assuming that in the beginning we had CO2, which was then split to organic carbon and O2 via photosynthesis. And now you are asking if it's possible to reverse all of that by burning all organic carbon, so that it consumes the O2. Your assumption is not quite right. Oxygen is the most abundant element in Earth's crust and ...


3

As Jan points out, there are many other factors in the oxygen balance, not just trees. But for a bit of fun, let us suppose that we burn all the trees on the planet. The global biomass of carbon is estimated as 47.4 PgC (it varies a bit according to season and inter-annual growth conditions). Of this we can estimate that the contribution from trees is about ...


3

Here's a somewhat different looking graph, from Oxygen and Evolution, Robert A. Berner et al., Science 316, 557 (2007): The graph shows three marked drops in O2 levels, each corresponding to an extinction event. These are intervals 4, 9, and 11. Interval 9, the largest such drop, represents the end Permian event about 252 million years ago. Interval 11 ...


2

"How can this be reconciled?" In two words: silicon dioxide :-) Yes, that's simplistic, but reflects the fact that virtually all the oxygen occurs in chemical combinations with other elements, not as free oxygen. The same is true for other elements in the crust & mantle.


2

The short answer is, $\ce{O2}$ is all around us! You aren't breathing the $\ce{O2}$ that the trees next to you are respirating (at least not much). No matter which way the wind is blowing, you will have sufficient oxygen content. A "can't breathe" feeling comes from inhaling pollutants or extremely dry air (in which case you need to drink more water). ...


2

Look at it this way: According to the American National Center of Atmospheric research, the Earths atmosphere weighs 5.148 x 10^^18 kg., and that atmosphere is composed of about 20.8 to 20.9% oxygen (depending on moisture content of the air). So the Earths atmosphere contains about 1.07 million trillion kgs of oxygen. The 7.5 billion (or so) humans on the ...


2

Estimates of earth's total biomass vary widely, from 0.5 to 4 trillion tons C, so instead of citing a source, I'll just go with an assumption of $1\times10^{15} \text{kg C}$. Measuring biomass in carbon is a convenient segue to the next assumption: assume that all biomass burns only in $\text{CX + O}_2\,\rightarrow\,\text{CO}_2 + \text{X}$. Given these ...


1

The main reasons the atmospheric oxygen remains constant are: The sheer quantity of it. Not even a large forest fire will measurably deplete it. Most of it is fossil oxygen created many millions of years ago by photosynthetic organisms. It is constantly being replenished by photosynthetic organisms, mainly in the ocean. Measurements of the percentage of ...


1

No, I think there are not. At least not at the scale of the proposed projects. I say this just because $\text{CO}_2$ makes up only a 0.04% of the atmosphere, so even if you burn fossil fuels until you double the pre-industrial amount of CO$_2$ and then capture and bury it back (both the Carbon and Oxygen). You would only drop Oxygen levels from its current ...


1

I just read an article saying that algae produces more oxygen than all the plants in the world!! Edit: https://www.nps.gov/romo/learn/nature/algae.htm First paragraph last lines


1

Based upon links from a similar question on atmospheric distribution in Chemistry SE, I looked into the latitudinal difference by making a couple images using the MSIS model chemistry plotting website (using Janauary 1, 2016, 100 W longitude, 0 km altitude) As I understand it, this suggests there is over 15% less oxygen at some latitudes than others. But ...


1

Vegetative photosynthesis does indeed have a significant effect upon atmospheric oxygen concentrations, as may be seen in the plots of the Atmospheric Oxygen Research. The strong seasonal variation in photosynthesis, particularly in high latitude northern hemisphere regions, results in an annual oxygen fluctuation of about 20 ppm (parts per million). ...


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