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There is a major legitimate scientific controversy that the article doesn't even get into, and it's about this claim: > "Dr Dutkiewicz said: “At this time, the

There is a major legitimate scientific controversy that the article doesn't even get into, and it's about this claim: > "Dr Dutkiewicz said: “At this time, there were no multicellular animals or land plants on Earth. The greenhouse gas concentration of the atmosphere was almost entirely dictated by CO2 outgassing from volcanoes and by silicate rock weathering processes, which consume CO2.”" This is really hard to be sure about - and the biosphere at the time was having steady major effects on the atmosphere, in particular atmospheric oxygenation via photosynthesis, which might have drawn down atmospheric methane - possibly the most important greenhouse gas at the time - leading to cooling (this is the biogenic origin theory of Snowball Earth). See: (2019) "Great Oxidation Event and Snowball Earth" https://ui.adsabs.harvard.edu/abs/2019asbi.book..261T/abstract https://ui.adsabs.harvard.edu/abs/2019asbi.book..261T/abstra... The subject is still open, with no highly convincing evidence for one cause or the other.

adrian_b 3y ago
Yes, that claim is weird. While there were no multicellular animals and land plants, there were abundant green algae (Chlorophyta), red algae (Rhodophyta) and blue-green algae (Cyanobacteria), both unicellular and multicellular, all of which were producing dioxygen, while consuming carbon dioxide. Because there where abundant algae consuming carbon dioxide, but the unicellular eukaryotes and bacteria that could produce carbon dioxide might have been less abundant, this should have had an important contribution to the decrease of the CO2 concentration. These 3 kinds of algae had already been abundant for several hundred millions of years, since more than a billion years ago. It is likely that the concentration of carbon dioxide had been decreasing for a long time and when there has been a time interval with diminished production of volcanic carbon dioxide, also accompanied with extra volcanic rocks able to combine with the existing carbon dioxide, all these have tipped the balance causing the glaciation, but the contribution of the excess algae has probably been greater than that of the CO2-absorbing volcanic rocks.

adrian_b 3y ago

Yes, that claim is weird. While there were no multicellular animals and land plants, there were abundant green algae (Chlorophyta), red algae (Rhodophyta) and blue-green algae (Cyanobacteria), both unicellular and multicellular, all of which were producing dioxygen, while consuming carbon dioxide. Because there where abundant algae consuming carbon dioxide, but the unicellular eukaryotes and bacteria that could produce carbon dioxide might have been less abundant, this should have had an important contribution to the decrease of the CO2 concentration. These 3 kinds of algae had already been abundant for several hundred millions of years, since more than a billion years ago. It is likely that the concentration of carbon dioxide had been decreasing for a long time and when there has been a time interval with diminished production of volcanic carbon dioxide, also accompanied with extra volcanic rocks able to combine with the existing carbon dioxide, all these have tipped the balance causing the glaciation, but the contribution of the excess algae has probably been greater than that of the CO2-absorbing volcanic rocks.