During the frozen period, known as "snowball Earth" the polar ice caps extended far down into low latitudes, covering much of the planet.

The emergence of the plankton, which incorporate carbon dioxide into calcium carbonate shells, created a new stability in the planet's carbon cycle, argue Andy Ridgwell, at the University of Riverside, California, and his colleagues. The minute organisms did this by providing for the first time a way to dump calcium carbonate into the deep waters below the open oceans.

Chemical processes in the sea that dissolve calcium carbonate deposits alter the acidity of the water. This helps regulate the amount of atmospheric carbon dioxide that can dissolve in seawater. And this in turn helps the planet to regulate its temperature...