Snowball Earth

Snowball Earth: The Story of the Great Global Catastrophe That Spawned Life as We Know It by Gabrielle Walker, Crown, 2003. 

Earth Freezing Over:

 In the 1960s Russian climatologist Mikhail Budyko considered the possibility of the Earth freezing over forever. Once the ice forms it reflects sunlight back away from the Earth, so the Earth cools: a positive feedback loop. Budyko thought that there was no way that this scenario could be reversed, so it must never have happened. 

Great Infra-Cambrian Glaciation:

The Infra-Cambrian time period was just before the Cambrian time period of the Paleozoic Era. In the 1960s Cambridge geology professor Brian Harland wondered why some equatorial rocks showed evidence of past glaciation. He thought that plate tectonics may have moved some icy plates from the poles to the equators. But he couldn’t explain all once-icy equatorial rocks in this fashion. Some rocks must have iced at the equator. He named this event the Great Infra-Cambrian Glaciation. 

Snowball Earth: 

The name Snowball Earth came from Caltech professor Joe Kirschvink. Joe discovered there had once been ice at the equator. Joe figured out that volcanoes releasing carbon dioxide and thus creating a greenhouse effect were the terminators of Snowball Earth. 

Cap Carbonates in Namibia: 

During the 1990s, Paul Hoffman spent five years doing fieldwork in Namibia. There he found many cap carbonates on rock outcroppings. Cap carbonates are limestone and dolomite sedimentary rocks. They are evidence of past glaciation. Hoffman thought that the cap carbonates in Namibia may have formed from Snowball Earth.

Volcanoes

Hoffman talked to a young colleague, Daniel P. Schrag, who was an expert in cap carbonates. Schrag suggest that a carbonate ocean had formed from the carbonic acid rain created from the carbon  dioxide spewed out from the volcanoes that melted Snowball Earth. He suggested that the cap carbonate sedimentary rocks had been formed by the carbonate-rich ocean washing over the rock dust produced by the grinding of the glaciers. In 1998 Paul Hoffman and Dan Schrag published a paper in Science presenting their Snowball Earth theory.