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55 million years ago, the world was literally a jungle. With such high temperatures, rainfall and humidity, life could proliferate. But 49 million years ago, something drastic happened: The Azolla Event, where ice was forming at the poles. The culprit? A kind of plant called Azolla. Within 800,000 years, photosynthesis and carbon sequestration from those plants reduced the atmospheric quantity of carbon dioxide from 3500 parts per million to 650.

enter image description here

[figure from Atmospheric carbon dioxide concentrations over the past 60 million years]

But the real question here is--did the cooling caused by the Azolla Event create a major extinction event of plant and animal species?

JohnWDailey
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  • I doubt the atmosphere had 3500 ppm of CO2 at any Tertiary period. See this graph: https://commons.wikimedia.org/wiki/File:Phanerozoic_Carbon_Dioxide.png –  Mar 13 '19 at 19:11
  • Interesting question. Can you add sources to all the facts you give of the Azolla event? – Camilo Rada Mar 13 '19 at 22:31
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    @CamiloRada https://en.wikipedia.org/wiki/Azolla_event – JohnWDailey Mar 13 '19 at 23:56
  • I added that link and info from some relevant sources more explicitly here. Interestingly, the authors of the paper where the CO2 concentrations in Wikipedia come from don't attribute the decline to the Azolla Event, they say "an erratic decline between 55 and 40 Myr ago that may have been caused by reduced CO2 outgassing from ocean ridges, volcanoes and metamorphic belts and increased carbon burial." – Camilo Rada Mar 14 '19 at 00:14
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    John: I understand why you stick to the figure of 3500 ppm, but giving that value as a set number does not acknowledge that there is an error bar larger than 1600 ppm on that value, the uncertainty is huge. In general, if for any reason you don't want to provide the uncertainties of a number, you should refrain from adding significan figures larger than the uncertainty. So you either say "between 2900 and 4600 ppm" or something more vague like "more than 3000 ppm". It is just a suggestion, of course you can phrase your question as you like. – Camilo Rada Mar 14 '19 at 18:41
  • I find the question very accurated, but, as I said, I doubt a bit those measures. The paper is from year 2000. Despite the picture I provided is in a different scale and from 2005, four authors wrote CO2 levels have been rounding 1000 ppm on Neogene and Paleogene, but I can be wrong and atmosphere could develop +2000 levels in Paleogene ocasionally. Anyhow I agree you need to consider the error in your graphs. –  Mar 15 '19 at 16:16
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    @Camilo Rada Ocasionally Paleogene levels look bigger (maybe), so from a previous question C. Sativa and other plants can be adapted to 2000+ levels on Tertiary and the adaptation is not inherited from Mesozoic. https://earthscience.stackexchange.com/questions/7627/how-did-plants-adapt-to-small-sfco-2-levels-past-400k-years-why-wont-they/15852#15852 –  Mar 15 '19 at 16:17

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