Swampy rainforests in Antarctica dated to the mid-Cretaceous
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Swampy rainforests in Antarctica dated to the mid-Cretaceous by UCD researcher
A new study has revealed the history of a temperate swampy rainforest that existed on Antarctica 90 million years ago, thanks to work from UCD. Earth Sciences researcher Dr. Chris Mark was part of the international team whose study was published in Nature this week.
In the study a sediment core was drilled from the Amundsen Sea in West Antarctica. The core dates to the middle of the Cretaceous period, one of the warmest periods of the last 140 million years. Atmospheric carbon dioxide levels were higher than 1,100 parts per million, and so studying this period gives insight into the worst-case scenarios of global warming, under which atmospheric carbon dioxide may reach this level within a hundred years.
The sediment core contained almost pristinely preserved soil from the mid-Cretaceous. This included pollen, spores and roots, giving an unprecedented look into conditions at the time. Studying the vegetation told researchers that 90 million years ago the area was a swampy rainforest with mean annual temperatures of 12 degrees Celsius. It is highly unlikely there was any ice on Antarctica at the time.
Dr. Mark, together with colleagues at Trinity College Dublin and the University of Bremen, performed the dating for a sandstone layer that capped the layers of mudstone and coal hosting the plant fossils. Dating this section was a challenge as the sandstones contained no fossils themselves. Instead Dr. Mark turned to measuring minute amounts of uranium and lead in individual mineral grains.
Tiny grains of zircon and apatite act as miniature clocks, recording the radioactive decay of uranium to lead over time. Even at low concentrations of a few parts per million of uranium, Dr. Mark was able to date the sandstones, providing an important age control on the timing of ancient Antarctic rainforest.