World’s oldest ice core could stretch back 5 million years

To learn about the future of Earth’s climate we can look to the past, and one of the best ways to do that is with samples drilled from deep ice cores. Now, scientists have dated what may be the world’s oldest ice core, with some sections potentially preserving samples as old as 5 million years.

The natural preservation ability of ice is dialed up to 11 in places like Antarctica, where tiny trapped air bubbles can capture pristine samples of the Earth’s atmosphere from thousands or even millions of years ago. Markers like carbon dioxide concentrations can be cross-examined with other ancient records to get a deeper understanding of what the climate was like in the distant past, and how things have changed.

Now a team of researchers may have peered back further than ever before with what could be the oldest ice core drilled so far. The sample was taken from Antarctica’s Ong Valley, where glacial drifts have deposited ancient ice relatively close to the surface, protected by a layer of rock. During the Southern Hemisphere summer of 2017 and 2018, the team drilled an ice core measuring 9.5 m (31 ft) long, and have since analyzed the age of material at different depths.

A section of the Antarctic ice core that may be the world's oldest, preserving material from as long as 5 million years ago
A section of the Antarctic ice core that may be the world’s oldest, preserving material from as long as 5 million years ago

Jaakko Putkonen

The researchers examined the accumulation of isotopes of beryllium, neon and aluminum throughout the core. These are produced by high-energy cosmic rays colliding with rocky material, and the concentrations can provide an indication of when a layer was last exposed on the surface.

From this, the team was able to calculate that the core is made up of two large ice masses stacked on top of each other, which may have occurred from two separate glaciation events. The upper section was estimated to be around 3 million years old, while the lower section was dated to between 4.3 and 5.1 million years. That’s almost twice as old as the previous record-holder, at 2.7 million years.

These are of course estimates, and while there may be room for error, the team says that analyzing three different isotopes makes them fairly confident of the age ranges.

While a glimpse of what Earth was like 4 or 5 million years ago is no doubt invaluable, scientists have their sights set on ice cores that preserve a continuous record of the climate. The current record-holder spans a period of 800,000 years, but scientists are aiming to collect cores that stretch back a million years uninterrupted. Some of these projects, including Beyond EPICA, are already several years into the drilling campaign.

The new study was published in the journal Cryosphere.

Source: University of North Dakota via Nature

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