After the machines took over, it seems that there is no significant organic life left on the surface of the planet. No sunshine ever reaches the surface, so there is no significant plant life to produce oxygen. The machine cities are unlikely to maintain the delicate balance of the atmosphere, because oxygen is corrosive to them. So, how can it be that there is breathable air on the surface of the planet after so many centuries (millenia?) without photosynthesis?

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    @AidanO: Because that's the definition of corrosion.
    – bitmask
    Commented Mar 1, 2012 at 8:55
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    @vsz When did you see a human walking on surface? Those who were outside Zion were in their ships.
    – user931
    Commented Mar 1, 2012 at 12:34
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    And, those who were captured by machines were facilitated by machines for oxygen.
    – user931
    Commented Mar 1, 2012 at 12:36
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    @bitmask "Corrosion is the result of a chemical reaction between a metal and its surroundings during which the metal is oxidized." Who says the machines are made of metal?
    – AidanO
    Commented Mar 1, 2012 at 13:32
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    @SachinShekhar At the very least there is oxygen in the old subway tunnels (at least twice the humans are seen walking in them), as well as in the machine city (seen when Neo hooks in to the Matrix through the machines to fight Smith).
    – Xantec
    Commented Mar 1, 2012 at 16:14

3 Answers 3


There would be residual oxygen from the time before sunlight was blocked out. Without sunlight and plants, most oxygen consuming life forms on Earth would have perished within weeks, if not days, which is not enough time to deplete a substantial percentage of the 20% oxygen atmosphere that we enjoy.

The machines would have taken care of the humans and their oxygen consuming industries. Natural oxidation would gradually take oxygen out of the atmosphere, but the Matrix is probably not old enough for this process to have made the air unbreathable.

You might ask what happens when oxygen is consumed by the humans plugged in to the Matrix. This plot hole is related to the plot hole about the viability of human bio-electricity. The only answer we have is that it is "combined with a form of fusion".

  • Unrelated to the question, but I'd like to know what you mean when you say there's a plot hole in "what happens when oxygen is consumed ... in the Matrix". Is this really a plot hole? The matrix is only a simulation that your mind is very connected to. You can't stay plugged in forever because you can't gain sustenance from it, someone would have to feed you in 'the real world'. Commented Mar 1, 2012 at 10:23
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    I didn't mean the virtual oxygen inside the Matrix. I was talking about the actual oxygen consumption by the humans inside the pods. They're submerged in a liquid medium which by necessity must contain oxygen.
    – HNL
    Commented Mar 1, 2012 at 10:55
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    @HNL That isn't really a plot hole either as the machines could manufacture oxygen for this purpose.
    – Xantec
    Commented Mar 1, 2012 at 16:15
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    @Xantec Using a "form of fusion", of course :)
    – HNL
    Commented Mar 2, 2012 at 3:18

Let's do some math, shall we?

According to Wolfram Alpha, a human consumes

  • 210 to 240 mL of oxygen (O2) per kg per hour

and weights around

  • 62 kg

which results in an oxygen consumption of

According to Wikipedia, 3/4 of the atmosphere are contained in an

which gives us a volume of


which results in

of breathing time for one human.

Since there seem to be no fauna (since there is no flora), this means that the handful of people living on earth can do pretty nicely.

You might argue that I didn't take into account the different pressure levels in the atmosphere when computing this (right at the start) but I only accounted for 3/4 of the oxygen that is available in theory. Also, thermodynamics tells us that the oxygen would be distributed across the planet equally, even if consumed only at one point (Zion).

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    @bitmask What makes you think that oxygen is consumed only by humans??
    – user931
    Commented Mar 1, 2012 at 12:40
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    There are some significant problems with that calculation, first being the calculation for the volume of the atmosphere. the atmosphere does not have a volume equivalent to a 11km radius sphere, but more appropriately, a spherical shell with inner radius of the earth, outer radius of that plus 11km. The atmosphere is also only about 21% oxygen. With partial pressure of O2 below about .16 bar (16% oxygen at sea level), humans begin to lose consciousness due to hypoxia. Even if the assumptions of oxygen surviving the machine war, the calculation is wrong.
    – Chris Bye
    Commented Mar 1, 2012 at 14:08
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    @Slothsberry: That's the point. Divide by a million if you like; It's still a billion years.
    – bitmask
    Commented Mar 1, 2012 at 15:24
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    @bitmask Beyond fauna and oxidation, there're fire, explosions, volcanos etc.. In war, very high amount of oxygen is exhausted. So, you need to take care of that...
    – user931
    Commented Mar 1, 2012 at 15:31
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    Not to mention that regardless of how much oxygen remains in the atmosphere the amount of chemicals toxic to humans is likely to be very high as well, due to the war, decomposing bio-matter, (machine) industry, rotting infrastructure etc..
    – Xantec
    Commented Mar 1, 2012 at 16:19

Actually, the comic The Miller's Tale (archived link here) indicates that there is significant plant life left on the Earth's surface. (It is part of The Matrix Comics released by the Wachowskis' company Burlyman Entertainment and was posted on the official website, so it is canon.)

Here are some panels from the comic showing plant life and fungi, and even small animals:

frogs and fungi plant fields weeds and forests grass

One of the last panels gives possible explanations for the survival of this plant life -- that genetic modifications and/or mutations have helped these "sun-loving plants" survive:


Since there is significant plant life left on the Earth, there is enough oxygen for humans on the surface of the Earth.

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