This graph presents an estimate of Phanerozoic CO2 levels on Earth.

enter image description here

From the onset of the graph, it appears that CO2 levels are rising. However, I've come across papers, such as this one, suggesting that Proterozoic CO2 levels were higher than those in the Phanerozoic.

I'm seeking a summary of how multicellular life has influenced Earth's CO2 levels to better understand our planet. I recognize that this topic is vast and could span an entire book. So, to narrow it down:

I understand that both foraminifera and other unicellular and multicellular organisms have been storing CO2 since the beginning of the Phanerozoic.

On the other hand, multicellular organisms, especially plants, have acted as CO2 sinks. This began during the Devonian-Carboniferous period. However, data suggests a declining CO2 trend since the Cambrian. This leads me to believe that the decrease in atmospheric CO2 throughout half of the Phanerozoic might be mainly attributed to shell-forming organisms. This brings me to a central question:

Which organisms have removed more CO2 in Phanerozoic and in total Earth's history, plants or shell organisms?

Additionally, I'd appreciate it if you could answer this other related question I've posted with a bounty.


1 Answer 1


It changes, there is no one overwhelming effect.

At some times plants have dominated at others ocean sediments have dominated. Position of continents, global temperature, sea level, and evolution of lifeforms all effect it.

Also you have a problem that those time periods are time PERIODS, the Proterozoic is 5 times longer than the phanerozoic. It had higher AND lower levels.




  • $\begingroup$ Do you trust te graph? It looks a linear tendency since Ordovician to Carboniferous. It looks not to register the plants huge event I learned from you is related with lignite. $\endgroup$
    – user29779
    Nov 26, 2023 at 15:05
  • 1
    $\begingroup$ @Universal_learner it looks exactly like the huge effects of plants is being shown, the lowest point is the carboniferous. you also have the formation of pangea, recovery from the last snowball period, and co2 removing tectonics events. arstechnica.com/science/2019/03/… As I said during different time periods and scales different causes dominate. also it looks more like a low resolution trend than a linear one. $\endgroup$
    – John
    Nov 26, 2023 at 15:28

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