We know that the world’s climate has changed drastically in the past.

After all, who among us didn’t grow up obsessed with dinosaurs, and aware that although they lived on a very warm, jungle-like planet, there were also great ice ages that drove other animals to extinction?

That said, it’s still kind of wild to see confirmation that even Antarctica looked vastly different at one point in our planet’s history – and it makes you wonder what it could look like in the future, too.

It was 44-34 million years ago, during the mid-late Eocene epoch, when parts of Antarctica were last ice-free. This left room for systems of rivers that brought sediments from the mountain range that spans the continent all the way to the Amundsen Sea.

This suggests there were no inland seas in between the two to hold onto those sediments.

During that time, there were glaciers in the highlands and the lower areas got snow during the winter, but also, forestlands flourished.

Those forests would have required regular rain and therefore rivers, but now that they’ve all long frozen over, it has been a challenge to track where exactly those rivers once ran.

IE: the current lowest point might not be the correct answer.

Professor Cornelia Spiegel and her colleagues decided to try to get to the truth by using the icebreaker Polarstern to drill into the sediment around the coast, rather than through the deeper ice on the continent itself.

The team found 56-79 feet of sediments in the Amundsen Sea that do not match those of West Antarctica, the nearest land.

Instead, they seem to have arrived from the Transantarctic Mountains, which divide East and West Antarctica.

This range runs across the continent, and the way the mountains sit, the team concluded the sediment had to have been carried by a river more than 932 miles.

It’s not objectively that long, but would have dominated West Antarctica, then and now.

The Transantarctic debris would have been deposited into a swampy river delta – like the Rhine or the Rio Grande, if using modern counterparts.

“The existence of such a transcontinental river system shows that – unlike today – large parts of West Antarctica must have been located above sea level as extensive, flat coastal plains.”

The authors concluded that a set of events, like depositing sediments in the Amundsen Sea, rift-related magmatism, seafloor spreading, and the rise of the Transantarctic Mountains, all took place around 44-40 million years ago.

It probably stopped around 34 million years ago when the world cooled and the continent began to freeze from top to bottom – or perhaps a seaway closer to the mountains developed.

Even though West Antarctica may be ice-free again (sooner than we would like), the team doesn’t expect the exact same river to return.

If you thought that was interesting, you might like to read about the mysterious “pyramids” discovered in Antarctica. What are they?