A few years ago, shortly before the COVID-19 pandemic, a group of scientists from the Alfred Wegener Institute in Bremerhaven, Germany, recovered and analyzed a 30-meter-long soil sample dating back 90 million years to the Cretaceous period from the ocean floor of West Antarctica. Analysis revealed that the sample contained traces of the southernmost forest ever found. Six years later, a new study by the same team on the same sample sets a new record: as reported above Nature Communications Earth and Environmentthat Cretaceous Antarctic soil shows signs of the most southerly fires ever discovered on the planet.
To avoid any misunderstanding, it is good to remember that we are talking about a period in which our planet was mainly populated by dinosaurs, which dominated many terrestrial ecosystems. Alongside them, reptiles and small mammals lived, but also insects and birds. However, there were no climatic and environmental conditions suitable for human survival, including the presence of ice caps at the Poles.
The fires of Antarctica
The sample found by the researchers is, as mentioned, 30 meters long, and was excavated “only” 900 km from the South Pole. When it was analyzed in 2020, it made it possible to discover that, 90 million years ago, Antarctica was not an expanse of snow and ice but a humid and swampy rainforest. To analyze a sample of that type, however, destructive methods are needed: in particular, the use of acids to dissolve everything that is not organic matter. In this way, traces of the plants remain, but the researchers at the time also noticed something they didn’t expect: pieces of coal, set aside awaiting further analysis.
Now these analyzes have arrived and confirm the nature of these small remains: burned plants, the first evidence of the fact that Cretaceous Antarctica was also crossed by fires. The sample also revealed other details that point in the direction of fire: the presence of certain chemical residues typical of burned plants, but also that of amber, which trees use to repair damage caused by external agents, including fire. If three clues prove it, then, the Antarctic sample contains remnants of the southernmost wildfires ever recorded.
From forest to peat bog
Fires that changed the face of Antarctica during the Cretaceous – another secret revealed by the soil sample, which allowed researchers to trace changes in the ecosystem over millions of years.
In fact, at the beginning of the sediment, in the deeper and therefore older layers, there is evidence of the presence of rainforests in Antarctica. With the arrival of the fires, which contributed to keeping the landscape more “open”, the forest began to make room for peat bogs, humid and marshy environments that benefit from fire: the authors point out that a similar mechanism fuels today’s Arctic peat bogs.
A fascinating detail that emerged from the study concerns sphagnum moss, the mosses thanks to which peat bogs are created. A comparison between sphagnum sphagnum spores from Antarctica, which date back 90 million years, and those found in Scotland from the last 10,000 years, showed more similarities than differences: in other words, these mosses have not changed much, and have continued to act as an engine for the birth and good health of peat bogs for tens of millions of years.
