Ice is usually ephemeral; it doesn't last that long before melting. But some ice on our planet has stayed frozen for millions of years, according to scientists on a quest to find the oldest ice.



It's chilly across the country today - highs of just 58 in Miami and 16 in Minneapolis, which makes Minnesota colder than Antarctica's McMurdo Station. But the cold weather doesn't last forever in the Twin Cities. And in Antarctica, it does. Ice there can last hundreds of thousands, even millions of years. And as NPR's Nell Greenfieldboyce reports, that makes Antarctica the perfect place to find some of the oldest ice in the world.

NELL GREENFIELDBOYCE, BYLINE: Just how old is the oldest ice on earth? John Higgins says, nobody really knows.

JOHN HIGGINS: You know, would I be surprised at this point if we had 5-million-year-old ice? I mean, I'd be surprised, but not - it's not unfathomable, I think.

GREENFIELDBOYCE: He and some colleagues recently collected ice samples in Antarctica that were later analyzed and shown to be as old as 2.6 million years. It's beautiful stuff.

HIGGINS: When you pull out the ice, it essentially is crystal clear, except it's filled with, you know, tiny bubbles.

GREENFIELDBOYCE: The bubbles contain air from when the ice formed. And this trapped air is what scientists are really after. Higgins says, if you want to understand how gases like carbon dioxide have affected the climate throughout history...

HIGGINS: You know, you can't really do better, other than getting a time machine and going back in time and taking an air sample, than using these ice cores, which, you know, physically just trap samples of ancient air.

GREENFIELDBOYCE: To release that ancient air, all you have to do is melt the ice.


GREENFIELDBOYCE: That's the sound of a research camp manager in Antarctica making drinking water by melting scraps of 200,000-year-old ice in a metal pot. To actually collect and analyze the released gases, however, ancient ice has to melt in a lab. Sarah Shackleton studies old ice at Princeton, where she gets to watch the trapped air bubble out.

SARAH SHACKLETON: And that is something that I don't know if I'll ever get sick of watching. It's actually, like, pretty mesmerizing. And one thing that's really surprising every time to me is just how much gas is actually in the ice.

GREENFIELDBOYCE: She says, it's a lot and, samples from time periods undergoing past climate changes could be used to help make predictions about the future.

SHACKLETON: One of the biggest questions in terms of kind of the modern warming and, like, anthropogenic climate change is, how much warming do - should we expect with the amount of CO2 that we have in the atmosphere?

GREENFIELDBOYCE: Now, Antarctica has been covered by an ice sheet for at least 30 million years, but it's actually pretty hard to find really old ice. John Goodge is a geologist at the University of Minnesota. He says, while snowfalls constantly add new layers of ice to the top of the ice sheet, the oldest layers at the bottom can disappear. That's because of geothermal heat coming up from the ground.

JOHN GOODGE: So the rocks are giving off heat slowly over time. And so that has the potential to melt ice at the bottom.

GREENFIELDBOYCE: Still, bits of super-old ice like that 2.6-million-year-old sample can sometimes be preserved at the ice sheet's edges.

GOODGE: The older snippets of ice that we've been able to find come from places where the ice has flowed up against a mountain range and been exposed at the surface.

GREENFIELDBOYCE: In those spots, though, the ice can be all jumbled up and messy. It's not in nice layers that have been laid down sequentially over a long, continuous stretch of Earth's history. To get a neatly layered ice sample like that, scientists need to drill straight down through the thick ice sheet. So far, the oldest ice collected that way goes back 800,000 years. Goodge says the goal now is to drill down a couple of miles to reach ice that's older, a million to 2 million years old.

GOODGE: Whether or not we'll be able to find it at the bottom of the ice sheet where we can recover a relatively simple continuous record is - I guess, that's the $64,000 question.

GREENFIELDBOYCE: A team from China has drilling underway. A group from Europe will start in November. What everyone wants is ice samples that cover a key time period, about a million years ago, when there was a dramatic shift in the planet's cycle of ice ages. Those had been coming every 40,000 years or so. But for some reason, that pattern ended, and it changed to every 100,000 years instead.

ERIC WOLFF: And to us working on climate, that's a really big deal.

GREENFIELDBOYCE: Eric Wolff is a climatologist with the University of Cambridge in the United Kingdom.

WOLFF: It's a really big question as to why that changed 'cause it's fundamental to how our climate system works. In a way, you could say, we don't really understand today's climate if we don't understand why we live in a hundred-thousand-year world rather than a 40,000-year world.

GREENFIELDBOYCE: The coronavirus pandemic basically ruined the Antarctic research season that would have been happening now. But starting next fall, researchers will be back down there searching for really old ice. Nell Greenfieldboyce, NPR News. Transcript provided by NPR, Copyright NPR.