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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.

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[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?

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  • $\begingroup$ I doubt the atmosphere had 3500 ppm of CO2 at any Tertiary period. See this graph: commons.wikimedia.org/wiki/File:Phanerozoic_Carbon_Dioxide.png $\endgroup$ – user12525 Mar 13 '19 at 19:11
  • $\begingroup$ Interesting question. Can you add sources to all the facts you give of the Azolla event? $\endgroup$ – Camilo Rada Mar 13 '19 at 22:31
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    $\begingroup$ @CamiloRada en.wikipedia.org/wiki/Azolla_event $\endgroup$ – JohnWDailey Mar 13 '19 at 23:56
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    $\begingroup$ 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. $\endgroup$ – Camilo Rada Mar 14 '19 at 18:41
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    $\begingroup$ @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. earthscience.stackexchange.com/questions/7627/… $\endgroup$ – user12525 Mar 15 '19 at 16:17

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