[JustDoItAlways]

To end the Snowballs, I’ve calculated CO2 levels would have had to increase to between 286,000 ppm (29%) to 800,000 ppm (80%) (and even more but that wouldn’t make mathematical sense unless the volume of the atmosphere increased as well).

There is not enough volcanic emissions of CO2 to come even close to those kind of numbers over even tens of millions of years.

The only estimate of CO2 at 715 million years ago is 6,000 ppm and the only one at 635 million years ago is 12,000 ppm.

[Steve Van Doorn]

notice at the time of the melting there was a great deal of 'something' theory is CO2. So much so it went from large packed ice to melted ice very fast.

I would suggest a large meteorite hit or very large caldera type volcano much greater then Yellowstone.