The Conversation: How a wobbly axis helped our planet escape 'snowball Earth

The idea of a deep-frozen world, "snowball Earth", has captured the imagination since first proposed in the 1990s. On several occasions in history, long before animals evolved, apparently synchronous ice sheets existed on all the continents. However, much like falling into a crevasse on a glacier, it's easy enough to enter such an ice age, but very difficult to escape.