Amanda Maxwell

Jul 22nd 2020

The Mid-Cretaceous Period and a Rainforest in the South Pole


If you ignore history, you’re doomed to repeat it; it’s a gentle, collective wake-up call to learn from the past. And a recent finding from the seabed not far from the South Pole presented climate scientists with just this opportunity. A mid-Cretaceous period core sample has yielded a tangle of fossilized roots that reveal an ancient rainforest.

When the planet was at its warmest and, as noted by, despite an annual four months without sunlight, temperate rainforest plants thrived over the Antarctic, which is now covered in ice. What lessons can the former jungle of Antarctica teach us about climate change?

A Tangle of Roots

Researchers from Germany and the United Kingdom published a paper in Nature that describes the unusual sediment layers in a core extracted from ocean bed around 560 miles (900 km) from the pole. Science Alert describes that when the scientists began examining the strangely striped bands, they could see a tangle of fossilized roots so well-preserved that detail was apparent even at the cellular level.

Upon analysis, they found that the species held in the geological time capsule were characteristic of a lush and temperate ancient rainforest. This meant that mid-Cretaceous period temperatures in the Antarctic were positively balmy compared with today’s icy habitat.

Mid-Cretaceous Period 101

CNN describes the mid-Cretaceous period lasting from around 80 to 115 million years ago. The entire Cretaceous period spanned the time from the Jurassic to the mass extinction event caused when an asteroid smashed into the Earth to create the Chicxulub impact crater. Pangaea broke up and sea levels rose.

In 140 million years of Earth history, the mid-Cretaceous is the warmest so far. Levels of carbon dioxide and greenhouse gases rose in the atmosphere driven by increased volcanic activity. This led to global warming with little difference between the poles the equator. Since the temperature gradient drives winds and thus ocean currents, the mid-Cretaceous period was characterized by warm but stagnant shallow seas.

And yes, there were dinosaurs; towards the end of the period, Tyrannosaurus rex and other powerful meat eaters roamed, while newly emerging mammals scuttled to find a safe niche. National Geographic describes how flowering plants established themselves, and we now know that swampy ancient rainforests covered the South Pole.

Secrets of the Deep

When the research team extracted the 10-foot (3-meter) core sample from the seabed, they realized that warmer temperatures also affected the pole. The sample — the southernmost Cretaceous core ever examined — showed that the landmass was not covered by ice as it is today.

One of the key features of the mid-Cretaceous period was abundant atmospheric carbon dioxide. Scientists previously thought that levels hovered around 1,000 parts per million (ppm). However, with the information from vegetation in the recent core sample, scientists had to revise their previous models. They compared species identified in the cores with plants growing today to determine a suitable climate for growth. They now estimate that levels of atmospheric carbon dioxide between 1,120 and 1,680 ppm would be needed to generate environmental condition suitable for ancient rainforests to thrive.

Lessons From the Past Inform Today

Climate change is leading to rising global temperatures. As well as altering global weather patterns, vegetation and habitats, warming is also affecting the poles. Glacier loss, thawing permafrost and melting sea ice impact polar wildlife survival and threaten to bring ancient disease back from the dead. One of the biggest proven drivers of global warming is the greenhouse effect; rising levels of carbon dioxide and other gases such as methane are trapping heat within the planet’s atmosphere. In 2018, NOAA noted that atmospheric carbon dioxide rose above 400 ppm. These are now the highest on record in the past 800,000 years. In the last 60 years, the rate of increase in accumulation has accelerated around 100 times; by the end of this century, levels are predicted to rise above 900 ppm without serious intervention.

At mid-Cretaceous levels, the South Pole was covered in ancient rainforest. Scientists already know that polar ice caps contribute significant cooling to the region. Known as the albedo effect, ice and snow fields reflect heat back into the atmosphere and away from the planet’s surface. According to The Verge, the loss of sea ice is responsible for around 25% of global warming. Losing Antarctic ice albedo would have similar impact.

Though we cannot predict exactly what a warmer world would look like, a tangle of fossilized roots from deep below the Antarctic seabed offers a glimpse of what our future might be.