In the frozen depths of the Allan Hills in East Antarctica, scientists have detected air bubbles trapped in the ice dating back 6 million years, the oldest atmospheric finding ever. Leading the research published on Pnas there is the team of Sarah Shackleton (Woods Hole Oceanographic Institution) and John Higgins (Princeton University), involved in the Coldex project, which for years has been trying to recover the oldest ice on the planet.
According to researchers, each ice core functions as an intact page of Earth’s history: tiny air bubbles remain sealed inside it, telling us what our planet was like when no human being existed. Here, however, there is an impressive time leap. Ed Brook, director of Coldex, also confirms this, surprised by the dating: they expected ice three million years old, not double.
The ice was dated thanks to the deficit of Argon-40, a noble gas which, compared with the current atmosphere, allows us to estimate the age of the trapped air. It is a sophisticated method, but essential when the ice does not form continuous sequences and the stratifications are difficult to reconstruct.
A mysterious layer of Miocene ice
Measurements of oxygen isotopes have allowed us to reconstruct past temperatures, showing a clear fact: between 6 million years ago and the Pleistocene, Antarctica cooled by around 12 degrees. Such an ancient direct measurement had never been obtained. This data is not just a number: it is a concrete trace of the climatic evolution of the white continent, a passage that helps to understand how glaciers responded to the natural changes of the past.
The new analyzes also confirm the value of ancient cores in reconstructing periods in which the Earth was warmer and with higher seas than today. It is a fundamental piece to understand what could await us in a future marked by global warming.
The team’s work also uncovered an enigmatic element: a layer of basal ice almost devoid of gas, too old to be dated with current techniques. But one detail immediately strikes scientists: that ancient ice has isotopic temperatures about 5 degrees higher than the oldest dated sample, the one dating back to 6 million years.
According to the researchers, it could be a surviving fragment of “adolescent” Antarctica, dating back to the Miocene, when the continent was not yet dominated by current ice. Perhaps it was simple snow or permafrost that remained intact as the East Antarctic ice sheet grew and incorporated everything in its path.
In other words, we may be looking at a remnant of the planet as it was before Antarctica became a glacial desert. This research, although complex, offers a simple truth to understand: ice not only preserves the cold, but the memory of the world. And the further we go back, the more precious that memory becomes.
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