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Why has CO2 decreased in the history of the Earth?

  1. Jun 21, 2015 #1
    I noticed that the Co2 is actually decreasing in the Eon time.

    My guess is lush vegetations or forests began to grow which absorbed the Co2 by photosynthesis? Would anyone give me any clue?
  2. jcsd
  3. Jun 21, 2015 #2
  4. Jun 21, 2015 #3


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    The concentration of any molecular species depends on the sources and sinks. When the rate of absorption by the sinks exceeds the rate of production by sources, then the concentration decreases. Sinks for CO2 would of course be plants (includes algae in the oceans and lakes) and animals, which tie up the CO2 and H2O in the form of sugar, cellulose, proteins, fat and various other large/complex organic compounds. CO2 would also form carbonates with minerals.

    Note that a lot of plant matter became coal, petroleum and an natural gas.

    The rise of free O2 should coincide with plants, both terrestrial and aquatic.
  5. Jun 21, 2015 #4


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    The creation of carbonate, oil, and coal deposits can account for a significant reduction in CO2.
    We have only had algae and plants in the last 1Ga so that does not explain the big initial drop.
    I think it would be quite difficult to get the data needed to draw the graph you show.
    The graph also looks like it is based on a hypothesis, not real data.
    Where is the graph from?
  6. Jun 21, 2015 #5
    A bit off the cuff here, but anyway
    When I was young It seemed to me that plants must grow because they get stuff out of the ground somehow by using light energy to push stuff up.
    It's more satisfying now I know that the majority of a plant's mass is made from atmospheric CO2, with only a bit of water and some other essential nutrients coming out of the ground.
  7. Jun 21, 2015 #6


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    What is the Y-axis? Is it %? If so, why does it show the atmosphere to be over 50% O2? This is not correct - it is about 21% O2.
  8. Jun 21, 2015 #7
    A more correct graph would be like this:
  9. Jun 21, 2015 #8
    Maybe, but still I think it is required in this forum to state the source when you are are offering information.
    (That huge spike of H2O early on is very interesting)
    Last edited: Jun 22, 2015
  10. Jun 22, 2015 #9
    Well, I got that off the images from Bing.
    There could be some extrapoltaion for earlier times.

    It is similar to one that can be found at

    where credit is given to the book Life in the Universe, Scientific American, 1995.

    The outgassing from magma is considered the main source of early atmospheric constituents.
    The lighter H and He would be lost to space.
    Any early O2 would combine with other elements, say Fe, for example, and depletion would be as rapid as production from UV with the H2O and CO2.

    Not only the atmosphere, but the oceans would have had to be of different composition that of today.
  11. Jun 22, 2015 #10
    Still, pretty much N2 all the way.
    Is there something unique about this planet which makes it, well a rocky planet with a mostly N2 atmosphere?.
  12. Jun 22, 2015 #11


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    That is a self referential question. If it was not, you would not be here to ask the question.
    Everything is unique when examined close enough.
  13. Jun 22, 2015 #12
    Eeeks, that's a tall order. We probably understand the CMB better than atmospheric interactions.

    As they say in real estate - location, location location. Add in the size of the earth with its gravitational field,and the composition of the nebula from which the solar system formed. Jupitor, which has held onto its gases quite well due to it being farther out from the sun and colder, and its larger mass and accompianing greater gravitational field, can be used as a reference to the nebula cloud constiuents.

    Being cold, in this case the part of the Jovian atmosphere that reaches into space, the percentage of molecules and atoms that have a kinetic energy that allow them to escape the Jovian gravity ( escape velocity ) is a tiny number. Put another way, the time for a molecule on the edge of the Jovian atmosphere to obtain escape velocity would be 10exp(x) where x is very large.

    For very early earth, being hot and lessor gravity, the original atmosphere from the nebula cloud would have pretty much escaped into space. 10exp(x) would be measured in years or thousands of years depending upon the species of gas. With cooling, ( note that it is not the actual surface temperature that predominates loss of an atmosphere, but the temperature at the "edge of space ), an atmosphere can be retained.

    Surface temperature, does though play a role in which elements can be locked up as compounds, either gaseous, liquid, or solid. The temperature dependance upon reaction rate may enable some compounds or species to become inert, such as the retention of N2 in the atmosphere, at a temperature sufficiently cool enough so that the 10exp(x) becomes large enough so that little is lost to space. ( Inert gases, not forming compounds, were never locked in and once released into the "early atmosphere" pretty much all escaped due to the higher temperatures at the earlier times ).

    Anyways, the story goes on with greenhouse effect to keep the earth surface warm and not frozen, UV production of ozone shileding the surface so that surface life could prosper, a change from a reducing atmosphere to oxygenated, an active planet with plate tectonics which enables recycling, condensation of water vapour to form the oceans, the magnetic field of the earth, increased output from the sun ( around 70% billions of years ago ), a long list..

    It is just tremendously facsinating what the earth has gone through in its history, so that we able to be here now. Are we lucky that just a little bit was not different and the earth did not end up as a Venus.
  14. Jun 22, 2015 #13
    From a powerpoint I downloaded from Umich AOSS department site. It seems to be made by a UM professor
  15. Jun 22, 2015 #14
    A predominantly N2 atmosphere is, I think, unique in this solar system,
    I wonder if any exoplanets have been discovered where that is a likely condition.
  16. Jun 22, 2015 #15

    Remove the Carbon dioxide from the atmosphere of Venus and what is left is mostly Nitrogen.
    Add in some life that oxygenates, and Venus could be much similar to the Earth.
  17. Jun 23, 2015 #16

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    I'm not thrilled with any of the graphs, including the one in the opening post. At least your second one is honest and starts with "ATMOSPHERE UNKNOWN". The scientific literature shows huge uncertainties. One thing is clear: There wasn't much oxygen until about 2.4 Gya (2400 million years ago). How much carbon dioxide and nitrogen there was is in the Earth's early atmosphere remains highly debated.

    That said, it's widely accepted that CO2 levels fell from an initially high value prior to the evolution of photosynthesis. CO2 dissolves in water. Some of that dissolved carbon dioxide became carbonic acid, which combined with rock to form carbonate rock.
  18. Jun 24, 2015 #17
    The whole thread question was probably answered by rootone in post 2, with CO2 consuming and oxygen producing photosynthesis, along with the removal of carbon by said geological methods, along with the formation of stromatolites from generations of cyanobacteria.
  19. Jun 27, 2015 #18
    "Extrapolation?" Duhhhh! Now who do you know on this blog who has been around in the pre-Cambrian period who can give the real data?
  20. Jun 27, 2015 #19
    Some silicates also absorb CO2, Volcanic sources provide tons of it, as well as CO2. New research indicates more absorption than production, over time.
  21. Jun 27, 2015 #20


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    Who wrote anything about extrapolation?
    In Geology, "the present is the key to the past", and we have the Geological Record. Extrapolation is only needed for forward prediction. Forty years ago I spent quite a bit of time studying the evidence of life in the Precambrian. I am happier interpolating within the geological record than extrapolating 1000 years into the future.
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