Between 256 million and 335 million years ago, the landmasses of the Southern Hemisphere were squished together in a super continent called Gondwana. Gripped in the cold throes of an ice age, glaciers moved slowly across the landscape, churning up ground and leaving a trail of sediment in their wake. They retreated as the Earth warmed, transitioning from an icehouse to a greenhouse climate at the end of the Paleozoic Era.