Ancient Antarctica was not always the frozen continent we recognise today. Beneath its ice and surrounding seafloor lies direct evidence of forests, warmer coastlines and ancient landscapes that existed millions of years before the modern ice sheet formed.

Sediment cores recovered near West Antarctica have preserved fossilised roots, pollen and spores from a temperate rainforest dating to roughly ninety million years ago. Other drilling records from the Wilkes Land margin contain evidence of palms, tree ferns and other warmth-loving vegetation.

These discoveries prove that parts of ancient Antarctica once supported ecosystems dramatically different from those found there today.

But evidence and reconstruction are not the same thing. The fossils and sediments are physical. The exact latitude of those environments, their seasonal conditions and the precise shape of the continent at the time must be reconstructed using plate tectonics, palaeomagnetism and geological modelling.

Around thirty-four million years ago, Earth entered a major climatic transition. Atmospheric carbon dioxide levels declined while the ocean gateways separating Antarctica from Australia and South America widened. Together, these changes helped create conditions in which a permanent continental-scale ice sheet could develop.

As the ice expanded, Antarctica’s geography was transformed. Glaciers carved valleys and fjords, former coastal plains were buried, global sea level fell and the immense weight of the ice pushed parts of the continent downward.

This creates an important problem when trying to reconstruct Antarctica’s lost coastlines. If the modern ice sheet were simply removed from a map, the exposed bedrock would not reveal the coastline of ancient Antarctica. Much of West Antarctica now lies below present sea level, while the crust itself has been depressed by the weight of the ice and would slowly rebound if that load disappeared.

Geological drilling also shows that Antarctica’s ice sheet has repeatedly advanced and retreated. During warmer periods such as the Pliocene, parts of the ice sheet were substantially reduced and global sea levels were considerably higher than today.

The evidence shows that Antarctica has changed profoundly. What remains open to continued investigation is exactly how its ancient geography looked at different points in deep time, and how quickly its vulnerable ice regions may respond to future change.

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