German geologists from the Alfred Wegener Institute have stumbled upon the remains of an ancient river system that existed in Antarctica tens of millions of years ago.

According to Report, the findings, published in the prestigious scientific journal Science Advances, shed new light on the continent’s surprising geological history.

The researchers’ conclusions are based on the analysis of sediments obtained from drilling into the seabed in West Antarctica. They determined that the lower part of the samples formed during the mid-Cretaceous period, approximately 85 million years ago. Remarkably, the sediment contained fossilized spores and pollen characteristic of a temperate rainforest, hinting at Antarctica’s dramatically different climate in the distant past.

The upper portion of the samples, dating back to the Middle and Late Eocene epoch between 30 and 40 million years ago, held another surprise. The sand in this layer exhibited a distinctive pattern reminiscent of the intricate designs found in the deltas of modern rivers, such as the mighty Mississippi.