Researchers from the Center for Oldest Ice Exploration (COLDEX), led by Sarah Shackleton of Woods Hole Oceanographic Institution and John Higgins from Princeton University, were able to extract fragments of ancient ice containing preserved air bubbles from a time when sea levels were higher and the Earth was significantly warmer.
Unlike deep-drilling efforts that seek continuous climate records, this project focused on isolated, shallow pockets of ancient ice. As noted in the study, published in the Proceedings of the National Academy of Sciences, this strategic choice allowed scientists to capture brief but critical “snapshots” of past climate conditions, windows into atmospheric composition, temperature, and ocean heat from a period six times older than previous Antarctic ice-core data.
Dating Bubbles From A Warmer World
The most ancient ice sample recovered from the Allan Hills dates back approximately six million years, a time when global temperatures and sea levels were significantly higher. Unlike traditional methods that infer age from nearby deposits, the team used argon isotope analysis on air bubbles sealed within the glacial core.
According to Earth.com, this direct dating process allowed for precise chronological placement without relying on local snowfall or ice flow assumptions. This technique has transformed what would otherwise be isolated patches into a cohesive climate library.
“Ice cores are like time machines that let scientists take a look at what our planet was like in the past,” said Sarah Shackleton, who has conducted numerous seasons of fieldwork in Antarctica.
The fact that these shallow layers preserved such ancient air provides an exceptional opportunity to refine understanding of how Earth’s atmosphere has evolved.
Scientists retrieve the drill that unlocked Earth’s oldest frozen record. Credit: Julia Marks Peterson/COLDEX
Six Million Years Of Antarctic Cooling
Alongside gas data, the team analyzed oxygen isotopes within the frozen deposit to chart temperature changes over time. Their findings reveal a regional cooling of roughly 12°C (22°F) across the past six million years, marking the first direct measurement of this kind from the Antarctic continent. The samples also capture brief intervals of extreme warmth.
This data could help evaluate the sensitivity of ice sheets to ocean heat and carbon dioxide during periods when the Earth passed key climatic thresholds. COLDEX director Ed Brook remarked that researchers initially hoped to find ice up to three million years old, but surpassing that by another three million was “beyond expectations.” The work confirms that these exposed patches of ancient frost, while discontinuous, hold extraordinary scientific value.
An ancient ice core that captured air from a warmer world 6 million years ago. Credit: COLDEX
A Harsh Environment, A Scientific Shortcut
Finding six-million-year-old ice just one to two hundred meters below the surface is only possible because of the Allan Hills’ extreme environment. The combination of strong winds that strip away fresh snow and the sluggish movement of the ice sheet has allowed ancient layers to remain near the surface, preserved but difficult to access. Shackleton noted:
“That makes Allan Hills one of the best places in the world to find shallow, old ice, and one of the toughest places to spend a field season.”
Despite the challenges, the Allan Hills method presents a shortcut to accessing Earth’s deep climate history without the need for multi-kilometer deep cores. COLDEX teams plan to return to the site in the coming months, aiming to expand the snapshot library and explore whether even older layers might be preserved nearby. As Shackleton put it, “The Allan Hills cores help us travel much further back than we imagined possible.”