A team of U.S. scientists has made a remarkable discovery in the Allan Hills region of East Antarctica, unearthing the oldest directly dated ice and air on our planet. This significant find, which includes 6-million-year-old ice and tiny air bubbles trapped within it, offers an unparalleled glimpse into Earth's past climate. The study detailing this discovery was published in the prestigious Proceedings of the National Academy of Sciences.
The oldest ice sample retrieved from the Allan Hills has been dated at an astonishing 6 million years, originating from a period in Earth's history characterized by much warmer temperatures and elevated sea levels compared to today. This pivotal research was spearheaded by renowned scientists Sarah Shackleton from the Woods Hole Oceanographic Institution and John Higgins from Princeton University. Both are associated with the Center for Oldest Ice Exploration (COLDEX), a collaborative effort involving 15 U.S. research institutions led by Oregon State University.
According to Shackleton, ice cores serve as "time machines" that allow scientists to explore what our planet was like in previous epochs. The Allan Hills ice cores enable researchers to delve much deeper into Earth's climatic history than previously thought possible. Ed Brook, the director of COLDEX and a paleoclimatologist at OSU's College of Earth, Ocean, and Atmospheric Sciences, described this discovery as the most significant to date for the COLDEX initiative. He noted that while the team initially aimed to find ice up to 3 million years old, the results have vastly exceeded their expectations.
COLDEX is one of several research teams globally engaged in a friendly rivalry to extend the ice core record beyond its previous limit of 800,000 years. Recently, a European team reported finding a continuous ice core that reaches back 1.2 million years in the interior of East Antarctica. In contrast, the COLDEX team is exploring a different setting for ancient ice, spending months at a remote field camp in the Allan Hills.
In their quest for ancient ice, the research group drilled down between 100 to 200 meters on the peripheries of the ice sheet, targeting locations where ice flow and rugged mountain topography converge to preserve old ice and make it more accessible. Recovering continuous ice cores from other sites in East Antarctica typically requires drilling more than 2,000 meters deep. Shackleton emphasized that the team is still investigating the specific conditions that allow such ancient ice to remain close to the surface. Factors likely include a combination of strong winds and extremely cold temperatures that inhibit ice movement.
The air trapped in these newly discovered ice cores allows scientists to directly date the ice using precise measurements of an isotope of the noble gas argon. This direct dating method enables researchers to measure characteristics within the ice itself to determine its age, rather than relying on indirect features. While the ice records from this ancient sample may not be continuous, their age is unparalleled.
By dating multiple samples, Higgins explained, the team has constructed a library of 'climate snapshots' that are approximately six times older than any previously reported ice core data, thereby complementing the younger data from cores found in the interior of Antarctica. Temperature records derived from measurements of oxygen isotopes within the ice reveal that this region experienced a gradual cooling trend of about 12 degrees Celsius (approximately 22 degrees Fahrenheit) over the last 6 million years. This research marks the first direct measure of cooling in Antarctica during this extensive timeframe.
As ongoing research into these ice cores continues, scientists aim to reconstruct levels of atmospheric greenhouse gases and ocean heat content, which are crucial for understanding the natural causes of climate change. A COLDEX team is expected to return to the Allan Hills in the coming months for additional drilling, with hopes of obtaining even more detailed snapshots and possibly discovering older ice. Brook stated that, given the remarkably ancient ice found at Allan Hills, they have devised a comprehensive long-term study of the region, aiming to extend the records even further in time between 2026 and 2031.
