What Space Dust Reveals About Earth's Ice Age

Cosmic dust can tell scientists about how ice covered Earth during the last ice age. This dust is leftover debris from asteroids and comets colliding in space and this dust constantly rains down on our planet. Researcher Frankie Pavia from the University of Washington recently used a brand new method for estimating climate conditions 30,000 years ago, by looking at the cosmic dust amounts in ancient arctic ocean soil. He and a team found new clues to what melted arctic ice at the end of the ice age. These results may be able to better inform ice melt in the future. Interested in more space science? Email us your question at [email protected] mailto:[email protected]. Listen to every episode of Short Wave sponsor-free and support our work at NPR by signing up for Short Wave+ at plus.npr.org/shortwave http://plus.npr.org/shortwave. See pcm.adswizz.com https://pcm.adswizz.com for information about our collection and use of personal data for sponsorship and to manage your podcast sponsorship preferences. NPR Privacy Policy https://www.npr.org/about-npr/179878450/privacy-policy

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• 0:56Regina Barber?

  Around 20,000 years ago, the world was cold. Temperatures around the world averaged 10 degrees Fahrenheit cooler than they are today, and most of North America was covered in ice. Humans were surviving, though, mastering fire and making friends with wolves.

• 1:12Speaker 02

  There's places where the ice is a kilometer thick, sitting on top of North America, the northern US and Canada.

• 1:19Regina Barber?

  That's Frankie Pavia, a geochemist at the University of Washington. And he says because the Earth's climate was so different during that time, the winds and oceans moved differently than they do now.

• 1:29Speaker 02

  And the sort of background state of Earth's climate, right, is just different as a result of both of these changes to the Earth's surface and, right, because there's 100 parts per million less carbon dioxide in the atmosphere during this time.

• 1:44Regina Barber?

  But in the couple thousand years to follow, carbon dioxide levels in the atmosphere and temperatures started to climb, and the Earth's climate began to change.

• 1:53Speaker 02

  It's a transition period. It's trying to get itself back to sort of a stable baseline state.

• 2:00Regina Barber?

  Today, our climate is changing too. But to understand that and the amount of ice we're losing, we need to know more about the past. That's where Frankie comes in.

• 2:10Speaker 02

  We're trying to figure out how ice coverage in the Arctic Ocean responds to climate change events in the past. Sea ice in the Arctic is a really fundamental part of the Arctic system as a whole, and it's declining quite quickly. And we would like to be able to predict what ice is going to be like in the future as we continue to warm the planet with fossil fuels.

• 2:35Regina Barber?

  So naturally, Frankie wondered, what if space could help us know more about Earth, specifically using something called cosmic dust?

• 2:42Speaker 02

  Cosmic dust is debris that forms from collisions of things like asteroids and comets in the solar system.

• 2:50Regina Barber?

  Cosmic dust blankets Earth's surface at a constant rate. And Frankie realized that this material from space could be key to finding out how the Arctic ice is melting now. So today on the show, what space dust is telling scientists about the history of ice in the Arctic and what that could tell us about the Earth's future. I'm Regina Barber, and you're listening to Short Wave, the science podcast from NPR.

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• 4:44Regina Barber?

  So Frankie, in a new study, you and your team tried to figure out how Arctic ice basically covered the Earth and how it's impacted by climate change. How do you get the sediment to study that?

• 4:55Speaker 02

  Yeah, so to get the sediment, you have to send a boat out, right, to the, to the part of the ocean where you want to collect mud. And essentially, what you're doing is you've got a big tube on the end of a long wire with some weight on top of it and a little device that self-closes at the end of it so that when you fill up that tube with mud, the mud doesn't all come sliding out when you raise it back up. And so you basically ram a big tube into the seafloor, fill it up with mud, right, with the oldest mud at the bottom and the youngest mud at the top, and then you haul that sediment back up to the ship that you're on.

• 5:33Regina Barber?

  If I also look at these tubes, how big would they be?

• 5:36Speaker 02

  The diameter of the tube is probably a little bit smaller than your, my face. And the length of the tube can vary from anywhere from like a foot to hundreds of feet long.

• 5:52Regina Barber?

  How are you analyzing these? Like, are they like in a lab and you're like looking at them or like, how are you studying them?

• 5:58Speaker 02

  Okay, so the these sediments are are taken, you know, raised up, they're processed either on the ship or on land. They're sort of sliced up about a centimeter at a time. And each layer, right, each of those centimeter layers is analyzed to figure out what time period that that mud is from and what sort of characteristics of the environment are recorded in the chemical signatures of that sediment.

• 6:28Regina Barber?

  Okay, so you're you're basically like going into the like the database and like looking at like information from all of these like centimeter thin discs.

• 6:37Speaker 02

  Yeah, so there's, you know, there's a there are repositories, there's basically huge libraries of mud that's been collected at the seafloor since the 1950s, more or less. Our Arctic mud is hasn't been getting collected quite as long as that, but right across the global ocean, you know, since the 1950s and even back to like the Challenger Expedition in the 1800s, people were taking samples of seafloor mud.

• 7:03Regina Barber?

  Wow. How much time is represented in this database of these like centimeter discs?

• 7:10Speaker 02

  From these sediment cores specifically that we worked on in this paper.

• 7:13Regina Barber?

  Yeah.

• 7:14Speaker 02

  We are going back about 30,000 years.

• 7:16Regina Barber?

  Wow. Okay. And in your study, you looked at something called cosmic dust inside the sediment cores. And cosmic dust is that debris that forms from collision of things like asteroids and comets in the solar system. How does this debris help you determine the age of ice?

• 7:32Speaker 02

  Yeah, so when that debris forms, right, it gets bombarded with the solar wind, which is right blowing out from the sun. And it's enriched in rare forms of helium because the sun is burning hydrogen to make helium.

• 7:51Speaker 02

  And so that helium with a sort of distinct fingerprint gets implanted into these cosmic dust grains. And those cosmic dust grains enter the Earth's atmosphere. So when they come in, they get heated, and only the really tiny grains, you know, less, you know, about one one-hundredth of a millimeter, keep their distinct helium fingerprint. And, you know, these cosmic dust grains then blanket Earth's surface at a constant rate in space and time over hundreds of thousands of years. And we can use measurements of that distinct helium fingerprint to tell us about how much cosmic dust is in sediment layers in the past.

• 8:33Regina Barber?

  And knowing how fast it settles on the seafloor depends on how much ice was covering that area. How do you figure that out?

• 8:40Speaker 02

  So I was actually studying cosmic dust in a part of the ocean that had nothing to do with ice. And I was using it in concert with one other sort of chemical index that we that we measure that nominally both tell you the same thing about how sediments accumulate at the seafloor. But they have different sources. So cosmic dust comes from space through the atmosphere to Earth's surface. And the other index chemical marker that we are looking at is produced in seawater. And when you have ice covering the Arctic, that cosmic dust that's coming in through space and then through the atmosphere gets intercepted by the ice and can't reach the seafloor.

• 9:21Speaker 02

  And we can detect that by measuring both our radioactive index and our helium fingerprint for cosmic dust.

• 9:28Regina Barber?

  Yeah, what'd you find?

• 9:29Speaker 02

  Yeah, so, right, I got together with my main sort of collaborator on this, Jesse Farmer, who's a professor at UMass Boston. And he had been working on Arctic climate change in the past for for some years. And We were sort of spitballing this idea and I was like, Jesse, is this, is this like a good idea? Is this really dumb? Is there some way to like, that we can get some Arctic sediments to test this?

• 9:55Regina Barber?

  Hmm, okay.

• 9:56Speaker 02

  And Jesse like had, Jesse sort of had the, the ideal set of samples for us to give this a whirl with.

• 10:03Regina Barber?

  Just sitting around?

• 10:04Speaker 02

  Yeah, um, truly. And so he sent me some little bags that had powdered sediment in them. Yep.

• 10:12Regina Barber?

  And the postal service was not mad about that at all?

• 10:15Speaker 02

  You know, this is, uh, this is, uh, sort of a, a funny thing when you're shipping these sorts of things. You do have to be like, this is, uh, you know, marine mud has no commercial value, blah, blah, blah. It doesn't look as insidious or suspicious as you might think, but there are geologic samples that do.

• 10:35Regina Barber?

  So you're looking at these baggies, you're looking at these samples and you're like, is this method gonna work?

• 10:40Speaker 02

  So we maybe measured like 10 samples to compare the top of the core, right? The most recent interval with samples that were from the last ice age, right? 20,000 years ago. And we found sort of immediately that there is a big deficit in the amount of cosmic dust.

• 10:59Regina Barber?

  Wow.

• 10:59Speaker 02

  Based on helium, right? That we would have expected during the ice age.

• 11:03Regina Barber?

  Okay. So that amount that you would just assume would be like, just accumulating on the, you know, on the ocean surface was just not right?

• 11:11Speaker 02

  Yeah, there was like a 300% deficit in how much.

• 11:15Regina Barber?

  Wow.

• 11:16Speaker 02

  Yeah, exactly. And so that's like, in the world, in the world of like geochemistry and paleo-climate, that is like, that is a real.

• 11:24Regina Barber?

  Pretty concrete.

• 11:25Speaker 02

  That is a real big signal, right? And so that was like, that's what set us off to the races of like, okay, we are, we might be on to something here.

• 11:34Regina Barber?

  So this deficit in cosmic dust says there, you know, or implies that there's, there was ice there. Why do we, as a human race, need to like know about the ice coverage during the ice age?

• 11:47Speaker 02

  Yeah, so that helps us say, okay, we've had these major shifts in climate, including conditions in the Arctic that were a little bit warmer than today. How does sea ice coverage respond? Because we've seen that over that last 40, 45 years, ice coverage in the Arctic has dropped by about 40%. And right, climate models try and make predictions of when the Arctic will be ice-free. And an ice-free Arctic has consequences for things like

• 12:17Speaker 02

  shipping and navigation for, right, geopolitics of Arctic bordering countries that are jostling for superiority there, for, right, fisheries, for coastal erosion of communities that live on Arctic coastlines. And so our goal is to figure out where there are major changes in climate in the geologic past that can help us, right, supplement the record of ice change that we've seen from satellites over the last 40 years, right, with longer time scales, with changes in climate that might be akin to where we're heading in the not-so-distant future.

• 12:54Regina Barber?

  So one of the findings that kind of surprised me is that what was melting the ice was maybe more clear than you thought.

• 13:04Speaker 02

  Well, it was and it wasn't. We were able to rule out one, right, so in order to melt this ice, you gotta bring heat in from somewhere, right? That's what's gonna melt the ice. And we had a few options, right? One was heat from warm waters entering the Arctic from the Pacific. One was heat from warm waters entering the Arctic from the Atlantic. And one was heat from the atmosphere. And based on the timing of when the Bering Land Bridge opened up and allowed Pacific waters to enter the Arctic, we could show that heat from Pacific waters entering the Arctic was not the cause of this ice breakup. And so that left us with

• 13:48Speaker 02

  Atmospheric warming, so direct atmospheric heating, or heat coming in from Atlantic waters. And we can't conclusively make a call between Atlantic-sourced heating and atmospheric heating. But more work that tries to unpack the mechanism for how you deliver heat to break up sea ice coverage during past Arctic climate change events would be really, really important to understand how that might be affecting ice coverage today.

• 14:21Regina Barber?

  So we're going to use your method more, and we're going to find out more.

• 14:25Speaker 02

  Yeah, and other methods, right? Like, other reconstructions that are looking at how different processes in the Arctic work.

• 14:34Speaker 02

  It takes a really holistic understanding of a lot of different things in the climate system and how they all operate together.

• 14:43Regina Barber?

  Frankie, thank you so much for talking with us today.

• 14:46Speaker 02

  Yeah, thank you. This is fun.

• 14:51Regina Barber?

  This episode was produced by Rachel Carlson, with a little bit of help from Hannah Chin. It was edited by our showrunner Rebecca Ramirez, and Tyler Jones checked the facts. Robert Rodriguez was the audio engineer. Beth Donovan is our vice president for podcasting. I'm Regina Barber. Thank you for listening to Short Wave from NPR.

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