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Yes, atmospheric oxygen is being depleted by fossil fuel burning. From https://cdiac.ess-dive.lbl.gov/trends/oxygen/modern_records.html - Oxygen concentrations are currently declining at roughly 19 per meg per year, or about 4 ppm per year. One "per meg" indicates one molecule out of 1,000,000 oxygen molecules, or roughly one molecule in 4.8 ...

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It is easier to calculate: The pressure of air on the ocean level is $\approx 100 \rm {kPa}$. Thus, its weight is $\approx$ 100000N over $1 \rm m^2$. Considering that the overwhelming majority of the atmosphere is below some km over the surface of the Earth, we can ignore the decrease of the gravity with height. Now calculate the mass of the air above a ...

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R. Tappert et al (2013) used carbon isotopes in ambers as proxies for atmospheric oxygen concentrations. Their work indicates an initial Miocene O2 concentration of 16% and rising to about 20% at the end: It's pretty remarkable how different their results look from other models. Some think that some inferred upward trend in O2 levels since the Eocene gave ...

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Since pre-industrial times $CO_2$ has increased from 280 to 415 ppm. Considering only carbon (ignoring the hydrogen in hydrocarbons), atmospheric $O_2$ decreased by the same amount, 135 ppm. The remaining FF are not much more than what has been burned, so the $O_2$ consumed will only be a tiny fraction of atmospheric $O_2$: Oil will end by 2052 – 30 years ...

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What filter? Modern vertebrate blood is always red (with just one exception AFAIK: https://en.wikipedia.org/wiki/Channichthyidae ) because it is based on hemoglobin. Given that birds, which descend from one branch of the dinosaurs, have red blood, it's likely that the dinosaurs did as well. Likewise plants are mostly green due to the chlorophyll used for ...

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