Oregon State University scientists and researchers from the Center for Oldest Ice Exploration announced in 2024 they had dated a 6-million-year-old ice core, found during the 2019-2020 Antarctic drilling season.
On Oct. 28, 2025, an official research paper — written by Sarah Shackleton, Valens Hishamunda, Lidsey Davidge, Edward Brook, Julia Marks Peterson and more — was released, revealing the significance of the historic finding.
“Antarctic ice cores provide the most direct archive of Earth’s atmosphere and its largest ice sheets. We report the discovery of ice, dated by its deficit in (the gas) Argon40 compared to the modern atmosphere, that is up to 6 million-years-old. Isotopic temperatures from this ice indicate progressive cooling over the Pliocene.” the paper said.
The Pliocene is a geologic time period that occurred about 5.3-2.6 million years ago. The paper also focuses on the Miocene time period that occurred before the Pliocene, about 23-5.3 million years ago.
The expeditions to the Allan Hills region of Antarctica — where the core was found — were and are ongoing through a partnership with COLDEX, a science and technology center formed in 2021.
Edward Brook, the director of COLDEX, worked with other scientists to get a grant that would allow for the continuation of ice core research.
“A few of us decided that we would compete for this science and technology center grant about old ice. Science and technology centers are these big entities that the National Science Foundation funds every three years… we just decided to put our hat in the ring… and went through… lots of review steps… there were hundreds of proposals, but we were lucky enough to be one of six that were selected,” Brook said.
Julia Marks Peterson, an OSU Ph.D. candidate, has been on two trips to the Allan Hills drill site with COLDEX and was one of the co-authors of the research paper.
Peterson said there is a reason scientists have been drilling at this site to find the oldest ice.
“People have been hypothesizing that this area of Antarctica has old ice for decades,” Peterson said. “The… meteorite community has… been going around dry valleys in Antarctica for a long time and found meteorites in this area (Allen Hills, Antarctica) with very old terrestrial ages that have been sitting on the surface for a very long time. So, glaciologists basically hypothesize if the rock is really old, then probably the ice surrounding it is also.”
The older the found ice is, the more clues it might give to what a warmer climate might have looked like millions of years ago. This helps predict how our current world might continue to react to the current rate of warming, which Peterson explained is why this discovery was so exciting.
“Getting back to warmer periods is one of the biggest motivations to try to find out more about the Earth’s climate state, both globally and regionally, during periods that are considered analogues. So definitely, this is the type of work that informs the climate models,” Peterson said.
There are multiple different studies happening with the ice within the other institutions of COLDEX as well.
According to Brook, scientists are studying not only the age of the ice but elements including neon, krypton and xenon that help them understand what the temperature of the ocean was like 6 million years ago. They also look at the dust trapped within the ice, as well as the sea salt content and what aerosols and gases were in the atmosphere.
The paper concludes by explaining that there will be future research happening with the cores that could help answer many important questions within paleoclimate science. This includes studying the “Antarctic ice sheet and its relationship to atmospheric greenhouse gases and mean ocean temperature with direct implications for future projections of sea-level rise, ocean circulation, and global radiative forcing.”
Read the full paper here at www.pnas.org.
