By Jenny Tindall
Antarctica is the coldest, windiest and driest continent on earth. With average temperatures ranging from −10 °C to −60°C and an average precipitation of roughly 50mm per year (half that of the Sahara desert), it seems a little farfetched to think that it was once home to a lush rainforest, similar to those found in New Zealand today. As strange as it sounds, researchers found just that. Around 90 million years ago, Antarctica was home to a temperate rainforest.
The world millions of years ago
145-65 million years ago, the earth was in the Cretaceous period. That means that yes, dinosaurs were roaming the earth and, that the earth was very hot. In fact in the mid-Cretaceous period, the earth reached one of the warmest intervals of the past 140 million years. So, what did these scorching temperatures mean for the coldest place on earth?
Recently, scientists in Antarctica found a sediment core from a seabed in West Antarctica. It looked different from most of their previous findings and they knew that it was something special. This core was a 3-metre long network of fossil roots embedded in mudstone. It had preserved roots, pollen, and spores that give us insight into what Antarctica looked like 90 million years ago.
This core indicates that in the coldest continent on the earth, there had once been a temperate rainforest. The pollen and spores are the first-ever discovered remnants of flowering plants found in these high antarctic latitudes. For this growth to be possible it is now suggested that the yearly average temperature must have been around 12 °C. With an average summer temperature of 19 °C. To put this into perspective, in Vancouver, the average monthly temperatures generally range from 1.6°C to 22°C. For Antarctica to reach these temperatures, there must have been a much higher concentration of carbon dioxide in the atmosphere than thought.
The Carbon Dioxide concentration
One factor of global temperature levels is the atmospheric carbon dioxide levels. Simply put, Carbon dioxide absorbs different energies emitted by the earth and re-emits it. This energy is what helps heat the earth’s surface. Right now the earth has a carbon dioxide level of 407.4 parts per million (ppm). Before the industrial revolution, the global average was 280ppm. Originally scientists assumed that the cretaceous period had a concentration of 1000ppm. However, the discovery of the core suggests otherwise. Model-based experiments reveal that it would need to be between 1120-1680ppm to allow the vegetation found, to grow.
With this concentration of carbon dioxide, it means that 90 million years ago there was most likely no ice cap at the South Pole or large land-ice masses. Ice masses that identify Antarctica today. In addition to this, it means that the rainfall back then would be similar to the rainfall in Wales today, rather than the 50mm Antarctica currently experiences.
This topic interested me because of how otherworldly it seemed. Who would have thought that a place that averages temperatures below 0°C was once dense with vegetation. Research like this opens a window into the world millions of years ago. I find this exciting and hope to learn more about topics such as this one.
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