6-million-year-old Antarctic ice reveals how Earth once heated; know what it warns about tomorrow

In a groundbreaking discovery, a team of US scientists has unearthed the oldest directly dated ice and air ever found on Earth, buried deep within the Allan Hills region of East Antarctica. The ice, estimated to be six million years old, preserves tiny air bubbles that serve as time capsules, offering an unprecedented look into the planet’s ancient climate.

The findings, published in the Proceedings of the National Academy of Sciences, reveal a period in Earth’s history when temperatures were significantly warmer and sea levels much higher than they are today. This ancient ice offers direct evidence of how the planet once responded to natural climate fluctuations that are increasingly crucial in the context of modern global warming.


Earth’s ancient ice discovered: Exploring Earth’s climate history

Led by Sarah Shackleton from the Woods Hole Oceanographic Institution and John Higgins from Princeton University, the study is part of the Center for Oldest Ice Exploration (COLDEX); a collaborative effort between 15 US research institutions spearheaded by Oregon State University.

“Ice cores are like time machines that allow us to see what our planet looked like millions of years ago,” said Shackleton, who has spent multiple seasons drilling at the Allan Hills site. “The Allan Hills cores help us travel much further back than we ever thought possible.”

According to Ed Brook, Director of COLDEX and a paleoclimatologist at Oregon State University, this is the most significant discovery yet for the team. “We initially hoped to find ice up to three million years old maybe a little older,” Brook explained. “But this discovery has far exceeded our expectations.”


Ancient ice preserved near the surface by Antarctica’s extreme conditions

Unlike traditional deep ice core drilling projects, which require drilling more than 2,000 metres below the surface, COLDEX researchers found this ancient ice closer to the surface just 100 to 200 metres deep.

The unique geography of the Allan Hills, with its rugged mountains and strong Antarctic winds, helps preserve and expose ancient ice layers that have been slowly pushed upward over millions of years. These conditions make the region one of the best places on Earth to find shallow but ancient ice.

“We’re still learning how such ancient ice survives so close to the surface,” Shackleton explained. “It’s likely a combination of extreme cold, strong winds that blow away new snow, and slow ice movement that keeps it preserved.”

However, the same conditions that protect the ice also make the Allan Hills one of the harshest field sites in Antarctica, with biting winds, freezing temperatures, and long isolation periods for researchers.


Dating ancient ice using argon reveals snapshots of Earth’s distant past

One of the most remarkable aspects of the discovery is the direct dating technique used. The team measured an isotope of the noble gas argon trapped within the air bubbles in the ice.

This method allows scientists to determine the ice’s age without relying on external clues such as nearby sediments or volcanic ash layers. Instead, the ice itself reveals when it formed, providing a more accurate and self-contained record of ancient climate conditions.

Although the recovered ice layers do not form a continuous timeline, they represent “climate snapshots” moments frozen in time that are roughly six times older than any previously obtained ice core data.


What the ice reveals about Antarctica’s ancient climate

Temperature readings derived from oxygen isotope measurements in the ice show that East Antarctica has cooled by about 12°C (22°F) over the past six million years. This marks the first direct measurement of the long-term cooling trend that transformed the region from a relatively temperate environment to the frozen continent we see today.

The study’s next phase will analyse greenhouse gas concentrations and ocean heat content preserved in the ice, helping scientists better understand how atmospheric carbon levels and ocean temperatures influenced Earth’s climate cycles before human activity began altering them.




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