When dinosaurs roamed the Earth 90 million years ago, the planet was much warmer, including Antarctica at the South Pole. But in a surprising twist, researchers have discovered evidence that Antarctica also supported a swampy rainforest at the time, according to a new study.

Researchers captured a slice of the seafloor using a drill rig aboard a polar research vessel on West Antarctica’s Amundsen Sea between February and March in 2017. The sediment core sample was taken near the Pine Island and Thwaites glaciers.

CT scans of the sediment core revealed pristine samples of forest soil, pollen, spores and even root systems so well preserved that they could identify cell structures. The soil included examples of pollen from the first flowering plants found this close to the South Pole.

They dated the soil, its fine-grained clay and silt to 90 million years ago. Their study published Wednesday in the journal Nature.

“During the initial shipboard assessments, the unusual coloration of the sediment layer quickly caught our attention; it clearly differed from the layers above it,” said Johann Klages, study author and geologist at the Alfred Wegener Institute. “We had found a layer originally formed on land, not in the ocean.”

Scientists know that during the age of the dinosaurs, conditions were warmer. The mid-Cretaceous era, from 80 million to 115 million years ago, was the warmest period for Earth in the past 140 million years, the researchers said. The surface of the sea likely reached 95 degrees Fahrenheit in tropical areas. And the sea level was 558 feet higher than it is now.

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