Traces of pollen, root systems and flowers have been buried beneath the seabed ever since the Cretaceous period, which lasted 146-65 million years ago. Now they have seen the light of day again, after a German-English research team made an expedition to Antarctica to dig for clues in the soil layers below the ice continent.

By tests and X-ray examinations of the sediment samples, researchers have now been able to determine that the coast of western Antarctica was swamp and rainforest, and that the average temperature was around twelve degrees during the year. Unusually warm for a place so far south. By comparison, today's average temperature in Germany is ten degrees.

Carbon dioxide contributed to high temperatures

The reason for the warm and green climate at the South Pole is believed by the researchers behind the study to be due to the high level of carbon dioxide in the air during this time period.

According to their calculations, carbon dioxide levels were up to four times higher than today, and up to twice as high as previous research has shown. The greenhouse gas kept it warm even during the four-month polar night that occurs over the Antarctic each year.

- The new thing is not that they found forests in the Antarctic, we have known this for a long time. But they present much higher values ​​of carbon dioxide levels in the atmosphere than previously thought to be, and these are new and interesting results, says Vivi Vajda professor of paleontology and head of unit at the Natural History Museum in Stockholm.

One of the hottest periods of time

The Chalk period was not just the time when dinosaurs roamed the earth. It was also one of the hottest periods of time. The sea level was 170 meters higher than today and it is believed to have been up to 35 degrees warm in the surface water in the most tropical places. But knowledge about the weather conditions around the South Pole has been limited.

- Scientists have long debated how it was possible to have ice-free poles while life could still exist in the tropics. At as high carbon dioxide values ​​as they present, the tropics should have been extremely hot deserts without multicellular life, but the fossil shows a completely different scenario; that the tropics harbored plants and animals, says Vivi Vajda.

The study “Temperate rainforests near the South Pole during peak Cretaceous warmth” can be read in its entirety in the journal Nature.