Settled science update: In the aftermath of Snowball Earth, CO2 levels were 90,000 ppm; or maybe they were 3,200 ppm, or maybe 400 ppm; maybe there wasn't a Snowball Earth

Cold Water Tossed on 'Snowball Earth' Theory | LiveScience

...So by comparing the ratios from the two sources, the scientists could get an idea of what the concentration of carbon dioxide was in the ocean, and hence the atmosphere, at the time.

They found it was much lower than expected. While previous estimates had put the carbon dioxide concentration at as much as 90,000 parts per million, this new analysis put it lower than 3,200 ppm, possibly as low as it is today, about 400 ppm.

"Since we record a very low carbon dioxide concentration in the atmosphere it seems to be there was never a high concentration of carbon dioxide in the atmosphere, which means it cannot have been a Snowball Earth, otherwise it would still be frozen," said Magali Ader, a study researcher and assistant professor at the Institut de Physique du Globe de Paris,.