Earth’s Atmosphere – What About The Oxygen?

The atmosphere of our planet has changed over geological time spans and I think it is worthwhile to reflect on what exactly that means for us and our future.

Carbon dioxide is released into the air through the process of combustion, burning of hydrocarbon fuels. When burnt, hydrocarbon fuels not only release carbon dioxide, they also release water vapor and consumes oxygen. We have increased the carbon dioxide content of the atmosphere from 280 parts per million to 367 parts per million. That’s an increase of 87 parts per million. We’ve decreased the oxygen content of the atmosphere also by 87 parts per million, because it takes one O2 molecule for every CO2 molecule produced through combustion.

Presently, the Earth’s atmosphere is approximately 78.1% nitrogen, 20.9% oxygen, .9% argon, .0367% carbon dioxide, and the balance is mostly water vapor. There are a number of trace elements, primarily other noble gases. Oxygen levels in the past have varied, but what I am learning is that there is no direct way known to measure ancient oxygen levels and depending on the method used estimates varied wildly. For example, on estimate had the oxygen levels as high as 35% 140 million years ago. The estimate was based upon insect size and other factors. Now another source estimates lower.

Primary factors that affected oxygen levels involved plate tectonics and sulfur. Exposing sulfur rich rocks in large amounts can rapidly deplete oxygen from the atmosphere.

Now, we’ve got a world hungry for energy, and burning hydrocarbons seems to be the method of choice for obtaining it. We really need to get away from this but there are many financial interests that would rather we stay the course. As a solution to CO2 emissions they suggest carbon sequestration, even though know proven technology has proven to be effective in the long term.

Carbon sequestration though also is oxygen sequestration because that CO2 taken and buried, took as much O2 out of the air in it’s formation. Folks, case you hadn’t noticed, human beings are somewhat dependent upon this oxygen atmosphere as is almost every other animal form on this planet, the only exceptions being some deep see worms near deep ocean thermal vents that have evolved the ability the use sulfur as an oxidizer rather than oxygen.

2 thoughts on “Earth’s Atmosphere – What About The Oxygen?

  1. Good point!
    I suppose our apparent margin of safety here is the vast difference in respective percentages of O2 and CO2 in the atmosphere. nevertheless…

    saw this related-
    Udall, former head of the Community Office for Resource Efficiency in Aspen and Carbondale, noted that the world is cranking out about 80 million tons of carbon dioxide every 24 hours, a statistic that has focused the world’s attention on global warming from greenhouse gases such as carbon dioxide.
He said that in order to produce that much carbon dioxide, the world must be burning approximately 30 million tons of oil, coal and natural gas per day, which he said translates into roughly 140 pounds per week, per person, globally.
    so we make 80 million tons of CO2 every day by burning 30 million tons of carbon?

    How can that be, unless  the difference the weight of the oxygen…?

    30 megatons of carbon + 50 megatons of oxygen = 80 megatons of CO2 ? is that it?


  2. Yes, that’s approximately right but the problem is more complex and dire than that.

    The build-up of carbon dioxide in the air is the difference between the amount that we create an the amount that is removed by various mechanisms.

    When I was in high school, the model we were taught is that animals create carbon dioxide, plants remove it, primarily the worlds forests, and thus we can save the world by planting trees. Ok, sounded good, I planted a few trees.

    But then I learned that 3/4ths of the oxygen removed by photosynthesis was removed by algae, and forests only account for about 20%.

    But after that I learned that only about 20% of the carbon dioxide sequestered by natural processes was by photosynthesis, the rest was through the weathering of rocks, mineralization.

    Now that last fact is where the big rub is; the carbon dioxide removed by photosynthesis, most of the associated oxygen is almost immediately returned to the atmosphere. Some is not, some is incorporated into the organism, but most is.

    But the 80% not removed by photosythesis, the oxygen associated with that carbon dioxide is tied up for hundreds of millions to billions of years. Eventually that crust will be subducted and melted, and some of that oxygen will be returned as carbon dioxide and water vapor from volcanoes, but that’s hundreds of millions of years from now.

    So while we’re building carbon dioxide at a relatively slow level; we’re removing oxygen at a much higher rate and that’s the part nobody is paying attention to.

    Now there is an industry push for carbon sequestration as a solution, that is to take carbon dioxide, inject it into salt formation to make minerals and 100% of that oxygen is gone for hundreds of millions of years.

    But it gets worse than that, because as the oxygen content drops, the dissolved oxygen content in water also drops. But in addition to lower levels of atmospheric oxygen there are two other factors driving oxygen levels down in oceans.

    One of those is the melting of polar ice, this is reducing the salinity of the polar water and it is that salinity difference that drives ocean currents. Because oxygen dissolves well in cold water but not warm, it is oxygen at the poles dissolving in the water that primarily oxygenates the oceans. But with the ocean currents slowing, the oxygen being taken into the ocean is slowing. The currents are already at about half the level they were a few decades ago.

    The other is that all the nutrients we are dumping into the ocean are causing algae blooms near the surface which is cutting off light from reaching any deeper preventing algae from making oxygen deeper and at the same time the dying algae sinking decaying eats up what oxygen is there.

    In the absence of oxygen, anaerobic bacteria that create hydrogen sulfide as part of their metabolism flourish. Hydrogen sulfide is what gives farts their wonderful odor, but it’s also a highly toxic gas and it only takes a few hundred parts per million to kill people and pretty much anything else.

    At least one mass extinction in the past has been the result of ocean currents changing, these bacteria blooming, and most of the Earth’s species going extinct from hydrogen sulfide poisoning.

    So to put it mildly the decreasing oxygen levels in the ocean are a REALLY BAD thing and we should be doing whatever we need to do to resolve this situation now.

    Beyond that, we get a large portion of our food from the oceans and that food depends on oxygen. No oxygen no fish.

    So the whole carbon dioxide sequestration thing is a BAD BAD BAD idea; what we really need to do is to find ways to either not produce the CO2 in the first place or recycle it back into oxygen right away.

    One way to do that and produce fuel at the same time is by farming algae, by making algae ponds which are enclosed and fed that carbon dioxide. There are some species of algae which will turn as much as 46% of that carbon back into oil for us, now how good is that?

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