# Has Earth's atmosphere lost mass throughout the geological ages due to biological $\small\sf{CO_2}$ fixation?

Stromatolites and other organisms have been storing $$\small\sf{CO_2}$$ in the form of $$\small\sf{CaCO_3}$$ throughout the geological ages, forming extensive limestone deposits scattered across Earth's crust.

Has this $$\small\sf{CO_2}$$ fixation process reduced significantly atmosphere mass?

Or, as part of a biological cycle, it hasn't changed the quantity of molecules of Earth's atmosphere and has only changed atmosphere composition?

• en.wikipedia.org/wiki/… – trond hansen Feb 7 at 13:25
• "A similar study in 2016 looked at the size distribution of gas bubbles in basaltic lava flows that solidified at sea level also during the Archean (~2,700 Ma). They found an atmospheric pressure of only 0.23 ± 0.23 bar (23 kPa)" - Paleoatmosphere – Keith McClary Mar 9 at 0:47

## 1 Answer

Yes, the Earth's atmosphere has thinned in the past few billion years, and biological fixation of CO2 was one of the main causes. It also gave us our present abundance of oxygen (21%). Enormous quantities of CO2 were used in the form of CaCO3 by foraminifera, corals etc to make their hard skeletons, and the resulting sediments formed limestone. Other elements formed compounds with carbonic acid (CO2 + H2O) to create other carbonate rocks.

In addition there is the more obvious sequestration of CO2 which was taken from the atmosphere by photosynthetic organisms and buried underground in the form of fossil hydrocarbons (oil, coal, gas, lignite etc). It was this which gave us our all-important oxygen. So the answer to your question is that biological activity has done both. It has hugely reduced the mass of the Earth's atmosphere, and at the same time greatly altered its composition.

It is also worth noting that the Earth loses substantial quantities of atmospheric gases into space, mostly hydrogen, but other gases as well. The bombardment of the outer atmosphere by ultraviolet rays, cosmic rays and the solar wind plays a part in this.

• Do you know from any paper or text book it has been thinned? We are starting to ask for citation when concepts are not very basic – user18590 Feb 7 at 10:19
• If you remove mass from the atmosphere, it does not have to get thinner: it can also get less dense. That's what my "common sense" tells me... – Jean-Marie Prival Feb 7 at 10:34
• Qualitativelly it can be common sense. Biosphere should have reduced atmosphere mass because of nature laws. But an answer could include studies about proto-atmosphere mass I don't find by my own. I am not saying your answer is wrong, but I have asked the need sources popup.Also, I wonder about the biogeochemistry behind. Someone could say that CO2 has been mostly transformed into O2. You say both, but you don't explain what happens in the biogeochemical cycle. – user18590 Feb 7 at 11:11
• Related to the question, I have searched some info this days about the topic and I don't find any paper saying proto earth atmosphere was similar to present Venus atmosphere. Earth could have less CO2 on his origins.If you find that info, please share it. – user18590 Feb 7 at 11:14
• @Universal_learner Michael is arguing from a en.wikipedia.org/wiki/Argument_from_authority. He has a high rep hence he is an authority and we must all listen without questioning him. – gansub Feb 7 at 12:37