Can supernovas cause ice ages?

00:00:07
Speaker 1: Hey, Jorge, been enjoying their recent run of rainy days.

00:00:10
Speaker 2: Yeah, I like a rainy day. It's kind of cozy.

00:00:13
Speaker 1: Well, I guess that's what we get for living in ice age rainy days. Even in southern California.

00:00:18
Speaker 2: Where we're in an ice age, I don't see any wooly mammoths around.

00:00:23
Speaker 1: Yeah, the wooly mammoths disappeared, and not just because the temperature.

00:00:27
Speaker 2: What happened They moved to a warmer planet.

00:00:30
Speaker 1: No, I think our ancestors turned them all into soup and blankets so they could be cozy on rainy days.

00:00:36
Speaker 2: Wait, that's not what I saw in the movie Ice Age.

00:00:39
Speaker 1: Not a documentary.

00:00:40
Speaker 2: It's also not TG I guess. I am Hore Makertoona and the author of Oliver's Great Big Universe.

00:01:01
Speaker 1: Hi, I'm Daniel. I'm a particle physicist and a professor at UC Irvine, and I live for the sunshine.

00:01:07
Speaker 2: Well, we all live because of the sunshine too.

00:01:10
Speaker 1: Right, Yeah, that's right. Almost all energy used by life on Earth comes initially from the sun.

00:01:16
Speaker 2: It grows vegetables and food, and that's how we can all stay alive and warm.

00:01:20
Speaker 1: Also, that's right, when you burn a piece of wood and you feel that glow. It's like it's released that original solar energy trees are basically solar energy batteries.

00:01:30
Speaker 2: Yeah, whenever I see a big green field that I always thinking, well, that's an awesome natural solar panel.

00:01:37
Speaker 1: I know, it is incredible that evolution has devised this way to eat photons and turn it right into chemical energy. Pretty amazing.

00:01:45
Speaker 2: Yeah. Yeah, although in between there's you know, a nice salad, and maybe more in between is a nice a piece of fried chicken.

00:01:55
Speaker 1: I like to think of all the photons in my.

00:01:57
Speaker 2: Salad, although it is a little heavy. It's not very light to have a fried chicken salad. But anyways, welcome to our podcast Daniel and Jorge Explain the Universe, a production of iHeartRadio.

00:02:09
Speaker 1: In which we try to shine a light on all the heavy questions of the universe. How does it all work? What are the smallest little bits? How do those come together to make grass and chicken and people and planets and stars and black holes and everything else that we see out there in the universe. It's an incredible, dizzying array of complexity, but we think it's possible to simplify it, to boil it all down into a few basic ideas that could be understood by you.

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Speaker 2: That's right. We try to serve up a nice, tantalizing buffet of amazing facts about the universe, amazing discoveries, and also incredible mysteries that we are still trying to figure out in a way that is hopefully not a word salad in your head.

00:02:51
Speaker 1: A crucial goal of doing physics is understanding the nature of the universe so that we can get a better sense for our context. Every time we learn something about where we are in the cosmos and how it works, it changes the way we relate to it, how we live our lives, what we think about it. And of course, at the center of our local cosmic neighborhood is the Sun, which is a source of all energy for life on Earth and could eventually fry everything on Earth.

00:03:14
Speaker 2: Yeah, because I guess it's easy sometimes to forget that we are just sitting atop a little tiny rock, flying around a big burning ball of gas in the middle of a gigantic space full of things that might at any moment kill us.

00:03:29
Speaker 1: It seems like sort of a precarious and fragile situation, Like if we didn't live it, and you read about it in a science fiction novel, you'd be like, hmm, that sounds kind of implausible.

00:03:38
Speaker 2: You mean, the idea that we were just like perched in the middle of a giant void where that might kill us at anytime.

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Speaker 1: Yeah, that we're the perfect place between a huge freezing void and an enormous ball of fire that could kill us, and we're in the Goldilocks zone right in between them.

00:03:54
Speaker 2: Yeah, and an orbit that is sort of miraculously stable, right, that just keeps going around the over and over again in a very stable way.

00:04:02
Speaker 1: It is sort of amazing that it's worked for this long, and we are grateful for it.

00:04:08
Speaker 2: It's amazing that the Sun arises every day because it could not, right.

00:04:14
Speaker 1: It could just stay in bed like your local cartoonists.

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Speaker 2: Yeah, yeah, that's right, thankfully.

00:04:21
Speaker 1: But the Sun and other stars out there are not eternal fixtures which will be pumping out energy to support life on Earth and alien planets forever. Sometimes they go boom. Sometimes they explode in enormous supernova which can fry their local region of space.

00:04:37
Speaker 2: Yeah. I think we're used to the stars being out their way out there and not really affecting our everyday lives other than making for nice night sky view here on Earth. But it is possible for those stars out there to actually affect us and maybe change the way that we live.

00:04:52
Speaker 1: That's right. It's not so crazy to imagine that our sun's variations as it gets brighter or colder as we move closer further away, could affect temperature on Earth and even potentially cause ice ages or global heating. But what about other stars out there in the universe. How susceptible are we to their.

00:05:09
Speaker 2: Quirks or their big explosive quirks for that matter. So to the podcast, we'll be asking the question, can super nova's cause ice ages? Well, I feel like that's two movie names and one title here, super novas, And I.

00:05:31
Speaker 1: Know, I know it means we're in danger of jumping the Shark, because now we're doing like bizarre mashups, you know, like Shark Tornado.

00:05:40
Speaker 2: I think we jumped to Shark a few hundred episodes ago, didn't we? And we're still here. We're still writing the Shark.

00:05:46
Speaker 1: I promise I didn't come up with this episode by randomly throwing darts at the wall with topic names.

00:05:52
Speaker 2: Maybe we should do an episode on the physics of sharks.

00:05:54
Speaker 1: Jumping, the physics of sharknados.

00:05:58
Speaker 2: You know, there's a lot of questions there. How do you launch the shark? What are the aerodynamics of the shark in air?

00:06:04
Speaker 1: Yeah, we have a crossover episode with Katie, she probably knows all about it.

00:06:08
Speaker 2: There you go, and then you could have maybe Henry Winkler the Fawns as a guest star, just to wrap it all up.

00:06:15
Speaker 1: And then we'll take a field trip and literally jump over a shark, just to hammer that point home. If people weren't getting it already, right.

00:06:23
Speaker 2: Right, I think that might be illegal, uh, and feel advised, but hey, if you want to go for it, I'll be unsure taking pictures.

00:06:30
Speaker 1: But this is not just a rim collection words mashed together for a new idea for an episode. This is actually something on the cutting edge of science.

00:06:38
Speaker 2: Yeah, the idea that maybe a supernova out there in space could have, maybe or can cause an ice age here on Earth. And so, as usual, we were wondering how many people out there had thought about this question or maybe even linked those two ideas together. I guess if it was close enough, we could do a lot of damage.

00:06:56
Speaker 3: One way or the other supernova was sent out heavy Adams and on a planet, if they pile up around the planet, they can block the other sunlight that's closer to the body and then calls ICAG just.

00:07:09
Speaker 4: Indeed, hopefully that doesn't mean the Sun, because I'm not sure if the Sun were to go super nova it would be cold enough for an ice age. But if it were like a close star, maybe some of the matter coming off of that star would shield us from the Sun and the temperatures were cool.

00:07:26
Speaker 2: I don't know.

00:07:27
Speaker 4: Seems far fetched, but I can't think of it any other way.

00:07:30
Speaker 5: This is a real if a butterfly flaps its wings on the other side of the world kind of question. Sure, a supernova would admit charged particles that would mess with a magnetic field and potentially strippinozone layer, so that would affect the climate dramatically. So yes, supernovas could cause ice ages.

00:07:47
Speaker 1: Thanks very much to everybody who participates. I love hearing your voices on the topics of the day. If you'd like to lend your thoughts to this segment of the podcast, please don't be shy wright to me. Two questions at Daniel and Jorge dot com. I'm pretty sure nobody ever regretted it.

00:08:02
Speaker 2: Would they tell you though.

00:08:05
Speaker 1: You know, people on the Internet are not shy to share their opinions, so I'm pretty sure I would get a grumpy email. If somebody's really grumpy about it.

00:08:13
Speaker 2: Well, I think if they regretted it, they wouldn't reply back again. So think about all the emails you're not getting.

00:08:20
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00:08:30
Speaker 2: Just havn't fill out a survey after every interaction with ten you have you enjoyed my talking with me? Please wanting to fill out the survey?

00:08:36
Speaker 1: No, then they're going to regret it because everybody regrets getting those surveys.

00:08:41
Speaker 2: Well, maybe you haven't fill out a survey about being asked to fill out.

00:08:44
Speaker 1: A survey, and then they recursively begin to hate me.

00:08:49
Speaker 2: Yeah, there you go, And as time goes to infinity, the universe will filled with it all approach to having gained zero.

00:08:56
Speaker 1: Knowledge and the band with the Internet will be surveys.

00:09:01
Speaker 2: But anyways, these are great answers from people. It seems like people think that maybe there could be a connection there in the same way that maybe a butterfly can flap its wing and I could get fried chicken the next morning because of that.

00:09:14
Speaker 1: Yeah, it's sort of a cosmic butterfly effect. Imagine a butterfly and alien planet triggering a supernova in that solar system, which then somehow makes ice ages in hours. Amazing power of butterflies.

00:09:26
Speaker 2: Yeah, and fried chicken as well. But this is an interesting question. Could a supernova out there in space somehow affect the climate here on Earth to the extent that maybe we actually get an ice age?

00:09:38
Speaker 1: Hmm amazing.

00:09:40
Speaker 2: So maybe let's start with the basics here that Daniel, what is the supernova and could one happen near us?

00:09:46
Speaker 1: A supernova is a really exciting and dramatic possible endpoint to a star. Not every star ends the same way. The fate of a star depends almost entirely on its initial mass. These stars are formed from huge clouds of gas and dust where something has triggered a gravitational runaway effect. So klump of stuff pulls together, and if it's too small it makes something like a brown dwarf. But if you get enough stuff in there, you can think of nice fusion and you can get a star and it can be burning. A lot of stars are kind of small. They're called like red dwarf stars, and those stars are just going to burn for a long long time and then eventually become like white dwarfs. Larger stars, though, when they run out of fuel that fuels what's preventing them from collapsing further gravitationally by providing pressure from the fusion inside of them. Larger stars, when that fuel runs out, they have so much gravity that they collapse, which then triggers an explosion at the heart of the star, which we call a supernova.

00:10:42
Speaker 2: But I guess a couple of questions there. First of all, do smaller stars ever run out of fuel? Don't they run out of fuel too? And what happens to them when they run out of fuel?

00:10:51
Speaker 1: Yeah, smaller stars definitely run out of fuel because they're smaller, their core is not as high temperature or as high pressure, so they go through their fuel more. So they can last for like billions and billions of years, but they eventually will run out of fuel and they'll just form white dwarfs. White dwarfs are just like their remnant of fusion. But it's no longer fusing. Like if you produce a bunch of carbon, but you're not hot enough to fuse carbon, then you just turn into a hot lump of carbon, and that white dwarf sits around for maybe trillions of years, glowing in space without fusing, until cools enough to become a black dwarf.

00:11:26
Speaker 2: But somehow there's a difference between that and a larger star because the larger stars collapse. The smaller stars don't collapse.

00:11:33
Speaker 1: Yeah, the larger stars have born gravity and so they can overcome the structural strength of the fusion remnants. Like the reason that white dwarf doesn't collapse further is that the structure of that big blob of carbon or nickel or whatever it's turned out to be is stronger than the gravitational forces. But if you have enough mass, you can overcome that and you can trigger another collapse, and that creates intense pressure and temperature at the core. So now you can fuse stuff you couldn't fuse before, and that creates very very fast, burning, very short lived reaction which causes an explosion again, which blows out a huge amount of material, and that's the supernova.

00:12:11
Speaker 2: Well, the other question I had was does the fate of a star also depend on what it's made out of, not just its mass, Like does a star with its pure hydrogen have a different fate than one that's more mixed in with other elements?

00:12:24
Speaker 1: Yeah. Absolutely, the amount of metal that a star starts with can really change the star's behavior. The more metal there is in a star, the more opaque it is to its own radiation, so the more it absorbs those photons rather than emitting it, So that can really change the temperature in the star, which changes the rate of fusion. And so the question of like how much metal each star starts with is really important one and one we're still trying to understand. We had a whole episode recently about how metal is our sun, and we know that it's like a couple percent metal, by which we mean things heavier than helium and hydrogen. But it is an important contribution, and so it's mostly determined by the mass of the star, but also other things like the composition, and it's not totally understood, like which star will go supernova is not something we can actually predict.

00:13:12
Speaker 2: Now, does this star having more metal make it more explosive or less explosive? Like it's being more metal, more radical.

00:13:23
Speaker 1: More metallic stars are more likely to undergo supernova and turn into neutron stars, whereas low metallicity stars are more likely to collapse directly into a black hole and might not even give you a supernova.

00:13:37
Speaker 2: Interesting. Yeah, I guess I would go straight into a black hole. Then there's nothing to explode out because nothing can get out.

00:13:42
Speaker 1: Yeah, exactly, But that's from like really massive stars above like forty times the mass of our star. In the intermediate region, like between ten and forty times the mass of our star. A lot of these will go supernova, but again it's hard to predict. It's a very chaotic event. In the moment at which a star is going to go supernova is not easy to tell. Like people have been watching Beetlejuice recently because it's brightness has become quite variable and they're wondering, like, is it about to go supernova? But nobody can tell when a star is about to go supernova. We don't understand the process, even in simulation. It's not something we know how to explain.

00:14:18
Speaker 2: Yeah, that's something that you said that also made me curious, was this idea we don't really understand this process very well. And I guess it's interesting that we haven't really studied supernova's very much, right, Like, we haven't been present when we see one. We haven't been up close to another star when supernova goes up, thankfully, maybe, But it's all sort of done through simulations and models of what we think is happening inside of a star from what we can gather from the kind of these pinpoints in the sky. Right.

00:14:50
Speaker 1: Yeah, we certainly have studied supernova, and you're right, a lot of the work is done in models. The reason we haven't studied more supernova is because supernova are really rare. It's not something that has depends all the time, sort of thankfully, otherwise we might have been fried out of existence.

00:15:04
Speaker 2: You know.

00:15:04
Speaker 1: In the Milky Way, for example, we expect there to be like two supernova's out of the hundreds of billions of stars every hundred years, and so it's not something that happens very often. And weirdly, we haven't seen a supernova in the Milky Way for a few hundred years. So that's another mystery we did a whole podcast episode about. But it's not something that happens often enough for us to get a lot of data. It's like spontaneous human combustion. You know, you hear about it happening occasionally. It's really hard to predict and so you have like sort of sparse data to work with to understand, you know, what might cause it.

00:15:37
Speaker 2: M I guess what makes it hard to predict, Like, isn't under signs that the sun goes through or the star goes through right before it blows up, Like doesn't it maybe ramp up in brightness or something.

00:15:48
Speaker 1: We'd love to know that. And it's really tricky because we can't monitor every single star until one of them goes supernova. They're just so many stars. So typically what happens is we see a star go supernova, then we start taking a lot of detailed data on it, but that's all post supernova. It we'd be very lucky to have been watching in great detail star just before it goes supernova, and that's one reason why we can't tell it stars go supernova. And from the theoretical side, it's very tricky because it's very intense physics. The stuff is moving close to the speed of light. It's very high density, it's very high intensity. There's a huge number of particles. The kind of calculations are very difficult to do correctly because not only are all the particles important, but it's very chaotic, like a small change in the structure of the star can lead to a large change in how that collapse happens and the shock waves. It's very complicated. I'm actually working with some folks at Berkeley who are doing supernova simulations, and each one of them requires running the supercomputer for millions and millions of hours, so we don't even have a lot of examples of supernova in simulation.

00:16:51
Speaker 2: Well, yeah, and I guess if you, you know, try to look for supernova and by looking at this guy all the time, you'd still be waiting, right, he said, we haven't had one in a long time. When was the last supernova that we've seen.

00:17:03
Speaker 1: In our galaxy? The last supernova was seen I think by Kepler, so four hundred years ago.

00:17:09
Speaker 2: Four hundred years ago, is it possible that one happened? What we didn't see it?

00:17:13
Speaker 1: Those are just supernova's in the Milky Way, And it's possible there have been supernova's in the Milky Way we haven't seen because we can't see through all the cosmic dust at the center of the galaxy. And weirdly, a lot of the supernovas we have seen in the Milky Way are far away from where most of the stars are. That's a whole funny, amazing mystery. But because supernova are so bright, we can also see them from other galaxies. In fact, when a supernova goes sometimes they're like a million or billion, or even a trillion times brighter than the Sun. They can outshine the rest of the galaxy.

00:17:45
Speaker 2: Yeah, they're super bright. But I guess any given time, isn't it true that we can only look at half of the sky, like the daylight side. We can't really see any stars, right can we?

00:17:54
Speaker 1: Yeah, that's right, we can only see half of the sky. And if you see a star in another galaxy go supernova, you can tell something has gone supernova. But we can't often pinpoint individual stars in other galaxies, so you can't be like, oh, it was that one over there and then go check your archival data to see what you know about it. So if we had more telescopes constantly studying the sky, then we could learn a lot more about supernova because we could see them before they go, which be really valuable.

00:18:21
Speaker 2: But as we just said, basically, you'd be waiting for four hundred years at this point, in which nobody wanted to wait that long to get a PhD.

00:18:29
Speaker 1: Yeah, exactly. And we have seen again in supernova more recently, like there's a famous one in nineteen eighty seven, very bright. You could almost even see it in the daytime from another galaxy, of course, not in the Milky Way.

00:18:40
Speaker 2: So they're sort of rare, but they do happen. And of course the universe in our galaxies are billions of years old, so many of them, probably a lot of them have happened since. And so the idea is that maybe the supernovas could somehow affect what life is like here on Earth.

00:18:56
Speaker 1: That's the question, yes, exactly, And so.

00:18:58
Speaker 2: Let's get into that question of whether a super and I can actually trigger an ice age here on this planet. So let's dig into that, but first let's take a quick break. All right, we're talking about supernovas and ice ages, both great movies, different audience.

00:19:27
Speaker 1: Though, what is the movie supernova? I haven't seen that one. I think there must be a movie called Supernova. Yeah, of course, you're right, there's a movie Supernova. Twenty twenty, Sam and Tusker are traveling across England in their old RV to visit friends. I'm not sure it's really about the supernova, but yeah.

00:19:47
Speaker 2: That doesn't sound like it's about astrophysics or space for that matter. Isn't there an older movie called Supernova?

00:19:53
Speaker 5: Oh?

00:19:53
Speaker 1: Okay, here's one from two thousand. This is a science fiction action film. Is it the one starting Killian Murphy? It chronicles the search and rescue patrol of a medical ship in deep space.

00:20:04
Speaker 2: All right, well, obviously it was not very popular.

00:20:11
Speaker 1: But everybody should go check it out. I mean, this one from twenty has an eleven percent rating on Rotten Tomatoes.

00:20:16
Speaker 2: So yeah, ja, I guess the movie didn't blow up.

00:20:21
Speaker 1: Yeah, I don't think it an ignited passion in the audience.

00:20:24
Speaker 2: Yeah, it just kind of collapsed under its own weight perhaps. But anyways, we're talking about whether a supernova that happens out there in space could somehow trigger an ice age here on Earth, which is because sort of mind blowing to think about that's something so far away that is explosive and hot can somehow make us cooler. Yeah.

00:20:44
Speaker 1: Yeah, it is amazing how interconnected everything is and how delicate everything is.

00:20:50
Speaker 2: Now we've talked about supernova's. Now let's talk about ice ages, and so what do we know about ice ages here on Earth?

00:20:56
Speaker 1: So ice age is a generic term for basically a period when Earth is cold, there's more glaciers, there's more polar ice, and if you look back at the history of life on Earth, you see these big variations in the climate. So there are times when like all of North America was under ice sheets, and then times when there's almost no ice on Earth. So it oscillates between like a greenhouse Earth and a snowball Earth.

00:21:21
Speaker 2: So they're just periods in time where things were cold.

00:21:24
Speaker 1: Yeah, exactly, And this is just what geologists have called these historic periods when the average temperature was much lower. But it's really fascinating because it tells us a lot about how climate on Earth. Works. And there's not just these big ice ages which lasts like millions of years, but there's also cycles within those ice ages. So within an ice age, there are glacial periods, which is when it's colder, and interglacial periods when it's hotter. So like currently we are in an ice age, but we're in an interglacial period. Of that ice age, so like on average it's colder than Earth has been in the past, but we're in a warmer period of that ice age.

00:22:02
Speaker 2: Well, yeah, I guess, first of all, it's kind of a mind blown to think that, you know, the Earth goes through these changes in these periods, like the Earth hasn't always been the same.

00:22:12
Speaker 1: It's sort of like a dynamic system. Yeah, it's definitely a dynamic system. And these ice ages date back like billions of years. One of the earliest ice ages we know about started like almost two and a half billion years ago, and then the more recent ones are all in the last like five hundred million years. But the Earth is definitely a dynamic and you know life on Earth has responded to it and influenced it. You know, early life, for example, couldn't tolerate the presence of oxygen, and then when oxygen started to be produced by photosynthesis, life then evolved to take advantage of that. And so it's fascinating how it's all interconnected.

00:22:48
Speaker 2: I guess the question is how do we know about ice ages from billions of years ago? Like, wasn't the Earth totally different? Do we still have evidence of those things?

00:22:55
Speaker 1: We know a lot about the history of the Earth from sort of three different categories of evidence. There's like geological evidence, there's chemical evidence, and then there's evidence from life, like paleontology. And so the geological evidence is like, let's look at the shape of the surface of the Earth. You know, about one hundred and fifty years ago or in the mid eighteen hundreds, people were noticing weird things they couldn't explain, like weirdly shaped valleys and like boulders and the alps that looked like they came from much further north in Europe, and like how did they get there. There's then that people postulated this idea that like glaciers move across the Earth and like create valleys and scrape out regions of the earth and can carry boulders with them for thousands of miles. So the geology of the Earth tells us a lot about the sort of history of.

00:23:44
Speaker 2: Glaciation, even though I guess rocks are constantly changing and moving and churning with the core of the Earth.

00:23:52
Speaker 1: Yeah, absolutely, there's a lot of things going on, but this is one of the processes and an important one for understanding sort of the shape of the surface of the Earth.

00:24:00
Speaker 2: Mm, so that's looking at rocks. How else can we know?

00:24:03
Speaker 1: So we can also take samples of the Earth because the different conditions on the surface are stored in the history on Earth. So, for example, if you go to the poles and you take ice cores, they do these amazing drills where they're like drilled into the ice one or two miles deep and then they pull it out. You can see layers from all the different winters on Earth. And in those layers you can measure like, first of all, the thickness of the layer, like what was the average snowfall? And there are trapped air bubbles in there which give you samples of the atmosphere from hundreds of thousands of years ago. And if you look at those samples of atmosphere, you can do clever tricks to figure out like how cold it.

00:24:40
Speaker 2: Was back then, yeah, and what it smelled like. Right, Basically you can smell the air from millions of years ago.

00:24:47
Speaker 1: Yeah, that's right. We might have some mammoth farts saved in the North Pole.

00:24:53
Speaker 2: Well, Takende, we we're all smelling mammoths farts right now because the same air molecules where around back then.

00:25:01
Speaker 1: Yeah, I guess that's true. And so the ice cores give us samples of the atmosphere up to like hundreds of thousands of years ago. And we can go even deeper into the path by looking at ocean sediment, like stuff that falls into the ocean and then settles to the bottom of the ocean. If you take cores of the ocean floor, you can again drill down really really far you find this sedimentation, and there's a lot of details about the chemistry of that sedimentation and what's deposited in the thickness of those layers that give you important clues about what was going on in the Earth's atmosphere, and that can take you back millions and millions of years.

00:25:36
Speaker 2: Well, you can tell how cold and hot it was.

00:25:38
Speaker 4: Yeah.

00:25:38
Speaker 1: Most of these clues about the temperature from the ice cores and the ocean sediment come from isotope ratios, because different isotopes of water, for example, have different chemistry and so like more of it will evaporate, for example, when it's hotter, and so the ratio of these isotopes you can back that out and figure out something about the temperature of the air, which is pretty yeah.

00:26:01
Speaker 2: Wow, it's sort of like carbon dating but water dating kind of.

00:26:04
Speaker 1: Yeah, exactly, and it's not trivial, right, there's lots of reasons why stuff on the ocean floor or in the ice cores can get confused, but it's an important part of this evidence. There's a really impressive scientific body of work here figuring out how to deduce this from these weird clues.

00:26:19
Speaker 2: Yeah, it's pretty amazing. And so we can also look at fossils.

00:26:23
Speaker 1: Right, Yeah, we can look to see where animals were, and we can look to see, like from fossils, where they lived and what the pattern and the climate might have been. You know, if you know that one kind of creature needs warmth and you see it in warm areas, you can also see where else you find fossils and that can give you a clue as to what the temperature. But the climate might have been like when they were around.

00:26:43
Speaker 2: So can you tell if there were sweating or if they were shivering.

00:26:47
Speaker 1: You can tell if their kids liked their dinners or didn't like their dinners by the amount of complaining and whining. That also changes the isotopes in the atmosphere. No, I'm totally making that up, but you know, you can tell what other organisms survive unchanged for millions of years, would tell you that the climate was likely stable for millions of years. So you can back out a lot of interesting information from these fossils. And for me, this is an example of the most impressive thing that science can do, which is like reconstruct a detailed story from all these incomplete threads, from little clues left here and there. We can really figure out what life was like on Earth, or understand what's inside the Earth or inside the Sun. From all this incomplete knowledge. It's like the whole universe is a huge mystery novel and we have just a few traces of clues. But sometimes those clues come together and tell you a coherent story, so you can become convinced that you actually know something which you might have thought would be impossible to figure out.

00:27:43
Speaker 2: Yeah, it's amazing. We can look back in time. Basically, it's like having a time machine.

00:27:47
Speaker 1: Yeah, exactly.

00:27:49
Speaker 2: And so what we've seen is that the temperature, the climate on Earth has been changing a lot, and it goes through ways and within those waves there are many waves. I guess a big question now is what causes all of these changes? Right? Like mm because the orbit around the Sun hasn't changed that much for billions of years, has it.

00:28:08
Speaker 1: Yeah, Well, there's a lot of factors of play, but one of them is the Earth's orbit. And this is a very complex system and very chaotic because there's a lot of feedback loops and we're gonna do some simplifications here and we're not gonna be able to really treat it with its full justice. But we do know some things about what can cause an ice age. You know. Number one is the atmosphere. If life on Earth produces a lot of CO two or a lot of methane, that can change the temperature on Earth for sure, right, And there's been times in Earth's history when life is producing more or less methane or more or less CO two, And so what's in the atmosphere can change, like how much light is absorbed by the Earth, how much is reflected back out into space, and because it's a sensitive system, that kind of an impact and even cause or end ice ages. But another big factor is the orbit of the Earth. There are these Melankovitch cycles, so the Earth orbits the Sun and it's you know, mostly stable, but there are wobbles here. Things process, and so there are periods when we work closer and further on average, and so these things really do change a little bit, and people think that this is a big effect of these glacial versus interglacial periods within an ice age.

00:29:14
Speaker 2: WHOA, what causes these wobbles in our orbit? Is it other planets or something else?

00:29:21
Speaker 1: Yeah, essentially, it's because it's not such a simple system. It's not a single mass orbiting another single mass. There's an excentricity, we have an axial tilt, we have a procession, and all of these things are interacting with the other gravitational objects in the Solar System, and so we get like little tugs from Jupiter and little tugs from other stuff in the Solar system, and these things change. So it changes like how much axial tilt we have and exactly the procession of our ellipse around the Sun. And as a result, we get slightly further or slightly closer to the Sun, and that changes how much energy we get. And these little effects can really cause a change in the climate.

00:29:57
Speaker 2: On Earth cool well or hot. I guess what else it can cause an ice age.

00:30:02
Speaker 1: Well, the Sun itself is variable, right, The Sun has an eleven year cycle when it gets brighter and looser, and then the north and south magnetic poles of the Sun flips. This is not something we understand very well. We don't really have a great model for the inner workings of the Sun. We know there are these weird plasma tubes, but it's again very chaotic, and we can't see inside the Sun. But the Sun itself grows in brightness and then fades, so that is part of the calculation.

00:30:28
Speaker 2: Like the Sun is pulsating.

00:30:30
Speaker 1: Years, yeah, exactly, and the Sun is gradually getting brighter overall, right, the Sun's brightness is increasing very gradually as it gets older. That doesn't change a lot over the last few centuries, but over the long term, you know, all these things do contribute to changes in the Earth's situation and therefore it's climate. And then you have things like volcanoes on Earth. If a volcano spews an enormous amount of stuff, it could create a cloud which shrouds the earth and cools it significantly. Or if you have like a meteor that comes and impacts and throws up ejecta into the atmosphere, or huge amounts of water vapor can also cause a lot of reflectivity.

00:31:09
Speaker 2: I feel really exposed right now, Like any of these things at any moment could throw us into deathly freezing temperatures or super duper unbearably hot temperatures.

00:31:20
Speaker 1: Yeah. And it's this incredible combination of slow changing effects and fast sudden effects like volcanoes and meteors. The last major component is tectonic motion, like as the plates move and as the continents themselves get dragged around the Earth, it changes how like water flows around the Earth and how wind currents move, and that can change the temperature all over the Earth, like are you getting more air from the Arctic? Is it getting fully distributed or is it more segmented. Can really change what it's like to be at lower latitudes.

00:31:53
Speaker 2: M Well. Also, something interesting you said was that we're currently in an ice age, meaning that over the long history of the Earth, the average Earth temperature is actually hotter than it is right now.

00:32:06
Speaker 1: I don't know the exact number about the average, but there definitely have been hotter periods on Earth than we have right now.

00:32:12
Speaker 2: Mm. So when you say it's colder, you mean it's just like colder than the hottest it can get.

00:32:19
Speaker 1: Yeah, the Earth is now colder than the hottest it's ever been. For sure, there are some very very hot periods in the history of the Earth. Of course, we know that the Earth's climate has changed a lot in the last one hundred ish years or so because of the Industrial revolution and human contribution to the atmosphere, and so things are changing pretty rapidly. But in the bigger strokes, we are still in an ice age, though in an interglacial period, right right.

00:32:42
Speaker 2: Well, I think, and maybe an important dimension of this idea is the rate at which things are changing, right mm hmm. Like maybe in the past things have changed, but maybe gradually, with enough time for life to evolve and to adapt to it. But it can also change rapidly, like for example, if it will case it blows up, or if a meteor hits the Earth, that can change things very rapidly to the point where we can that or if we keep you know, pumping greenhouse gases into the atmosphere, that can also make things change too rapidly for anyone to adjust.

00:33:14
Speaker 1: Yeah, it's a sensitive system and there are a lot of things that affected and those things all have different time scales, and they combine to make a very chaotic sort of structure of the Earth's climate, and you have these things that are very slowly but inevitably, like the sun increasing in its temperature or regularly, and then the Melankovitch cycles, which are actually like several different cycles layered on top of each other. So as a result, you gets very complex behavior of the Earth's climate, and it has affected life on Ear even very recently, like this interglacial period that we're in only started like ten to fifteen thousand years ago, and obviously there were lots of humans on Earth back then, and that's back when there were more wooly mammos and there were glaciers much further down across North America, for example. And so this is sort of like in the deep history, maybe even the deep memory of our own civilization.

00:34:04
Speaker 2: The humans have written out some of these waves, is what you're saying.

00:34:08
Speaker 1: And these waves have affected human migration, right, there's all these theories about humans leaving Africa and populating Europe and doing so in several waves between ice ages perhaps, so it's really set the whole context for life on Earth and the evolution of humanity and its migration. It's basically the frame in which we exist whoa.

00:34:27
Speaker 2: That is pretty cool, maybe even ice cool.

00:34:30
Speaker 1: It's definitely cosmic.

00:34:31
Speaker 2: All right, Well, we talked about different things that can maybe trigger changes in the climate, But the question we're asking today is can a supernova from a star blowing up far away from here? Can that maybe affect the temperature and climate here on Earth? So let's dig into that idea. But first let's take another quick break. All right, we're asking a question can of supernova cause an ice age? Which is kind of a triggy question, right because supernovas are big, explosive, hot, deadly impactful, But an ice age here on Earth is sort of slow and cold and you know, freezing. So how can something exploding far away cause things to get cooler here on Earth?

00:35:25
Speaker 1: So the connection is still kind of tenuous, but it's sort of fascinating. The idea is that supernovas, they don't just go boom and send out a bunch of light in the sky. They also send out dust, like little bits of those supernovas that get carried along by like cosmic and galactic winds and can come here to Earth. And when supernovas do go boom, they make sort of unique materials. They make stuff that you can't otherwise make in the universe because you just don't have the conditions. Like stars, they confuse hydrogen into helium, and helium into carbon, and carbon into heavier stuff all the way up to about iron, but they can't make anything heavier than that because above that it costs more energy to fuse than fusion creates. So all the heavier elements in the universe are made under much more special conditions, such as neutron star mergers or during those moments of supernova fusion. The explosion that creates the supernova also can create weird new heavy isotopes of elements and also heavier elements, and some of those bits can fly through the universe and even land on Earth, potentially affecting the climate here on Earth.

00:36:33
Speaker 2: Right, Because I think as a start collapses and becomes a supernova, it collapses, then it crunches together, and then it bounces, and then everything just kind of blows out in all directions, and that shock wave is where a lot of the heavier elements get made. Because things are being exploded out and compressed so much they become heavier elements. And you're saying that stuff being flung out can actually maybe reach us at some point.

00:36:55
Speaker 1: We know that it has reached us, and we found evidence of it here on Earth. This one particular kind of element is called iron sixty, so it's a heavy isotope of iron. This is something which can be made under other normal circumstances. But it's interesting because that's a fairly short half life, just like two and a half million years. So if it was present on Earth when Earth was formed, for example, all of that would have decayed away into nickel. So if you find iron sixty on Earth, that means it was made fairly recently, sometime in the last five to ten million years. But there's no process on Earth that can make iron sixty. The only way we know that you can make iron sixty is in the heart of a star, especially in a supernova. And so if you find iron sixty on Earth, that's very strong evidence that you found remnants of a supernova here on Earth, like supernova dust has landed on Earth.

00:37:47
Speaker 2: WHOA wait, how do you know it's not just really old iron sixty from when the Earth was formed? Cann't you just have a bunch of it and some of it still survived, like we still have uranium on Earth.

00:37:57
Speaker 1: We do still have uranium on Earth. Uranium is on much longer half life than a couple of million years. The Earth is four and a half billion years, which is many, many lifetimes. This stuff has a lifetime of two and a half million years. And if there was original primordial iron sixty, you would be evenly distributed and you'd see a sort of typical decay. Well, what we find when we look for iron sixty is we see depositions consistent with an increased amount of iron sixty like tuish million years ago, and maybe like another deposition like a million years ago. It really looks like we got fresh doses of iron sixty a couple of times in the recent past.

00:38:34
Speaker 2: Well you mean like we've seen basically coatings of the Earth with this iron. Yeah, isotope exactly, and there's several coatings.

00:38:43
Speaker 1: There's several coatings, and if you just like dig down into the earth, you don't find this stuff. But on the ocean floor you do see it, and you can see it in the sedimentary layers. You could see it like layered at certain times and not other times. And so it's really consistent with like the Earth blasted with supernova iron sixty.

00:39:03
Speaker 2: Well, I wonder if you would see it on one side of the Earth, you know, or not the other, or would you see it evenly coating the whole earth.

00:39:09
Speaker 1: Yeah, that's a great question because we'd love to know where these supernova were, right, which direction did they come from? And if you saw, like where it landed on the Earth, you might be able to like reconstruct that not just from which side it's on, but like where is it more dense? And Unfortunately on Earth, these things tend to get swirled around a lot. Like on the ocean floor, things get mixed around, and so you can tell it's there, and you can tell what year it was deposited. But you know, over millions of years, these things do get swirled around and spread out. But if we went to the Moon, the moon is a much better place to keep these sort of ancient geological records because you know, there's no weather on the Moon, there's no water, there's no air, and so where things landed on the Moon is pretty much where they still are. So the Moon might have a great snapshot if you measure the iron sixty on the surface of the Moon to figure out which direction these things came from.

00:40:00
Speaker 2: Well, we've been to the Moon and we've gotten samples from there, and what do we find in terms of this iron?

00:40:07
Speaker 1: We didn't find very much, But the samples are not really the kind you would need to answer this question. You know, Apollo landed on the near side of the Moon, and much more likely these things landed on the far side of the Moon because it's facing out, and so we'd need much broader sampling also to like reconstruct the direction. And so if you wanted to answer this question from samples on the Moon, you need to sample very differently from the way Apollo did. So we don't really have the data we would need to answer that question. One more reason to go back to the moon.

00:40:38
Speaker 2: So the Earth has gone in a few dustings of this iron from potentially supernova's. What's the connection to an ice age? Then, so there's a couple of things. One is they can look at the timing of the supernova and it looks like there was a string of supernovas that went off in the last ten million years in our galaxy. It's like a blob of deposition of iron sixty from like one point seven to three point five two million years ago. And then there's another deposition like two and a half million years ago and another one zero point eight million years ago that they think are consistent with supernova's that went off like around three hundred light years away from the Earth, And the time of these things kind of lines up with the timing of the ice ages. So if you look at the history of the climate on the Earth and you look at the history of these supernova, you can like kind of line these things up. Now that's just correlational, but it's intriguing and it makes people wonder like, hmm, could the arrival of this iron sixty on Earth somehow trigger climate effects which lead to ice ages? WHOA. But I guess maybe one question people might have right now is these supernova were super duper far away. Three hundred light years is gazillions of kilometers away. Could there still be enough iron in that explosion this far out? Wouldn't it be super diluted and spread out, it would actually be a significant amount that we could see.

00:41:53
Speaker 1: It's a great question, and it highlights the incredible numbers that are going on here. Like, first of all, when you make a supernova, the mounts of material are vast because supernova come from really big stars right, So you're starting with an incredible number of atoms. But then, of course, as you say, space is huge and we're far away from these things, so how are we getting any of them? And the answer is that we're not getting many. The number of iron sixty atoms, we've recovered numbers in the thousands. So we've scoured the planet for these things, and people have done these incredible missions to the bottom of the ocean. We don't have a lot of examples. We have enough to reconstruct the timing of these things to say something about which direction maybe they were coming from, but we don't have a large number of examples.

00:42:36
Speaker 2: No, meaning, this is a very faint signal.

00:42:39
Speaker 1: It's a pretty faint signal, but it started out so bright and so intense that even this far away we can't pick it up.

00:42:46
Speaker 2: Now, then, how can this iron affect the climate here on Earth?

00:42:50
Speaker 1: So that's something people are more speculating about and trying to understand. Is not a solid model here, but you can imagine that the arrival of heavy metals in the app sphere could change the way things circulate and the way things nucleate and the atmosphere chemistry, which is very complicated and so there isn't like a very clear argument here yet. I mean, I was reading some papers that were kind of hand wavy. But the general idea is the atmosphere composition is an important component of understanding the climate, and changes in the atmosphere can change the climate. We know that's true. And so the question is can iron sixty or how much iron sixty would have to arrive to trigger a change in the climate that might give you an ice age. That question is not answered, right.

00:43:33
Speaker 2: It seems like you wouldn't get I mean, if we were talking about thousands of atoms, that doesn't seem like a lot enough to trigger and ice it. But maybe the super wall that send other things besides iron, right, Like, maybe it's send other elements, Absolutely a ton of other elements.

00:43:47
Speaker 1: Yeah, And we have found thousands of atoms. Of course, we have a tiny detection efficiency, which means there are many, many more atoms actually arrived on Earth. And you're absolutely right, the iron sixty is just like one of the easiest things to identify. Along with it must have come all sorts of other debris from the supernova. And when you get unusual, weird cosmic dust from space that might trigger changes in the atmosphere, but it's kind of speculative. I think the most suggestive piece of evidence is the coincidence between the timing of the ice ages and the timing of these recent supernova although it's hard to tell if that's a coincidence or not.

00:44:21
Speaker 2: I see, they seem correlated, they seem to be happening at the same time, but we don't know how yet or how that's even possible exactly.

00:44:29
Speaker 1: And you know, this is the process of science. You see this weird effect, you wonder if they could be connected. You look for a mechanism. Rather than just saying, oh, look, it happened at the same time, therefore one cause the other. You try to dig into it and understand, like, how could that be? Is is there a way that could really happen, and how could we check that? And so some people are working on that right now, like trying to understand what kind of supernova debris might trigger a change in the atmosphere.

00:44:52
Speaker 2: Interesting. It made me think that you know, the supernovas happened really far away, right and they're huge, and which maybe affect the entire Milky Way galaxy or a big part of the Milky Way galaxy, in which case, like one of these supernovas exploding could maybe trigger an ice age in a whole bunch of planets around that start, right.

00:45:12
Speaker 1: Yeah, absolutely, And when the supernova happens, it like sterilizes the nearby planets. It's cool to think it could have a more subtle effect on even further away planets, right, it can change the climate of those planets, which could really affect the evolution of life on those planets. Like maybe life is more likely to become intelligent when there are ice ages or when it's oscillating ice ages and warm periods. Who knows, right, But supernovas definitely have a rippling effect on the whole history of the galaxy, and that changes the whole frame for life everywhere in the galaxy.

00:45:43
Speaker 2: Yeah, it's definitely a cool effect. And like you said, like maybe it's possible that the only reason we evolved is because of a supernova. Like maybe even that supernova hadn't happened and sent all this material here, we wouldn't have evolved.

00:45:56
Speaker 1: Yeah, or we could have evolved very differently, you know, migrated differently, had different patterns and paths if the climate were different, and so life on Earth could be vastly different without that super Nivah.

00:46:06
Speaker 2: Yeah, without that iron in which case it means Daniel, I think that we're all ironmen. It's not just Tony Stark, that's right.

00:46:17
Speaker 1: Oh, you don't have to run a marathon and bike fifty miles and swimed in miles all the same time to be iron man. You just got to live here on Earth and listen to podcast.

00:46:28
Speaker 2: And or build an armor, yes, a robotic armor.

00:46:31
Speaker 1: Awesome. Well, I'm looking forward to writing my own saber tooth cat to work.

00:46:35
Speaker 2: And then yeah, you're looking forward to jumping your own prehistoric shark.

00:46:39
Speaker 1: Right, that's right, exactly, sabertooth shark.

00:46:42
Speaker 2: Yes, or maybe you should start a new meme or term, right, jumping the saber tooth tiger. We're jumping the wooly mammoth. Oh that sounds even better, you go, yeah, we really that podcast was great, but then it jumped the wooly mammoth, and you know, now it's even better.

00:46:58
Speaker 1: Yeah, well, maybe we're entering the vast podcast ice age.

00:47:01
Speaker 2: Yeah. Thanks are definitely cooling a little bit here, all right. Well, another reminder of how carrious life here on Earth is to all of these cosmic events that are happening all around this and maybe hopefully make your appreciate the fact that we are here talking about these things. And then maybe that fact is only possible because of a certain string of events that happened billions of years ago.

00:47:22
Speaker 1: Our curiosity to understand the universe continues to burn hot, even if the heat of those stars eventually causes an ice age.

00:47:30
Speaker 4: Right.

00:47:30
Speaker 2: We hope you enjoyed that. Thanks for joining us, See you next time.

00:47:39
Speaker 1: For more science and curiosity, come find us on social media where we answer questions and post videos. We're on Twitter, Discord, Instant, and now TikTok. Thanks for listening, and remember that Daniel and Jorge Explain the Universe is a production of iHeartRadio. For more podcasts from iHeartRadio, visit the iHeartRadio app, Apple Podcasts, or wherever you listen to your favorite shows.