[Insert Your Own Catchy Title About Younger Dryas Here]

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I'm Josh, and there's Chuck and Jerry's here, too. And this is Stuff You Should Know. And what we've got on our hands today, Chuck, is a hot potato of a real-deal geological mystery. Hot potato? That's how Emily Spamley says potato. I think I would only say it when it's preceded by hot. I would only say it like I wouldn't say I'm going to have a baked potato. Like you'd be out of your mind to say it like that. Nor would you say a hot potato. Like what a square. Yeah, that is pretty square, isn't it? Get the stick out of your butt, fellow, loosen up. Right, loosen up. Get the cardigan out from around your shoulders. Yeah, jeez. So that was obscure, but still. So like I said, this is a mystery today. And just to give a brief brush stroke overview, the widest brush, real lot of space in between bristles, just barely any paint on it, that kind of overview. Oh, wow. What we're talking about is something called the Younger Dryas, which is a pretty, it's a pretty terrible name for this if you want to be catchy, right? Yeah, I mean, I think a lot of people will probably say WTF. Right. Well, let's just call it the YD if we're going to, if we're going to put initials on things, how about that or abbreviate things? So the YD, the Younger Dryas, is this, the surprising shocking period in Earth's history, fairly recent history, where we came out of the last ice age, everything was going smoothly, and then bam, we got hit by another ice age out of nowhere. That lasts for over a thousand years. And then bam, it goes away just as fast as it came along. And paleogeologists, paleoclimatologists, all the paleos are perplexed as to what caused it and then why it stopped so suddenly too. That's why I said it's a real deal geological mystery. Yeah, and a time as we'll see where the Earth and its inhabitants and the animals and nature was all going like, all right, thank God, we can finally get down to business and start being an Earth, like a legit Earth. And then, you know, the YDs come along and say, not so fast. Right. And you call it a legit Earth because when it finally ended, and actually that period in between the last ice age and the YD, those are like really habitable for human beings. Like we love those kind of conditions so much so that after the YD ended, it became the age of humans. Yeah. Like this is the age where we began our civilizations. We started farming. We began to flourish as a species and basically take over the planet. And what's interesting is this is the most recent ice age. There have been seven in Earth's history. And just as an aside, this was the Wisconsinian ice age that we're talking about. The last one was 250 million years before. Right. So it's pretty significant that we just, geologically speaking, came out of an ice age because there's not that many. And then not coincidentally, when the second to last ice age ended, that opened the door for the dinosaurs to come along and take over the Earth. So things, big things happen when an ice age changes. So for it to switch back to an ice age all of a sudden and then switch back to nice and temperate for us humans, it is just very weird. It was actually, I've seen it described as an extreme weather millennial event. Yeah. And, you know, it kind of made me wonder, had this not happened, because we were sort of headed toward, you know, legit Earth, like I said before, you know, I mean, it would obviously wouldn't change the year, but let's say as far along this goes, we would be like the year 3000 something, right? Like would we be just that much further along as a planet? Or would we be nowhere? Because in a thousand years, we will have already destroyed ourselves. The second one. Okay. All right. So it's a good thing this happened, or we wouldn't be talking about it right now. Exactly. That's exactly right. So yeah, that's a really anthropic way of looking at it. Well, speaking of. I bought a copy of If Anyone Builds It, Everyone Dies, the Eliezer Yucasci-Nate Sora's book that just came out. Okay. It did not know about it. You say that as if it was just on the tip of my tongue, which I appreciate. No, you do. We remember I basically mischaracterized it in the Zizian's episode and had that book, right, about building AI. And if anyone builds it, then we're all going to die, like just the existential threat of AI. It is really good. You could read it in, if you had a day that you could dedicate to reading it, you could read it in a day. It's really popularly written. Lots of really cool anecdotes. It's just very good. So I strongly recommend that book. Great. Okay. So let's kind of just back it up a little bit and go to the previous Ice Age, the Wisconsinian Ice Age, and talk about what Earth looked like, like that. Yeah. So it was, it was very icy. There were huge ice sheets covering a lot of Earth, like most of North America, Northern Europe and Asia. And as we'll see, a lot of the, the YD is affected, the Northern Hemisphere, much more than the Southern, but also weird things happen in the Southern Hemisphere that don't quite jive. That's why it's such a kind of a strange mystery. But lots of ice everywhere. We had barren plains, very harsh conditions. We had things like, you know, woolly mammoths, like ice loving creatures dwelling the Earth and, you know, human populations that were sparse and scattered and, and constantly kind of moving around, trying to survive. Right. And so that the last Ice Age started about 100,000 years ago, and it took about 80,000 years to reach its peak point. So 20,000 years ago, it hit what's called the last glacial maximum, right? So it took 80,000 years to get there. And then 10,000 years to basically melt. It melted a lot faster than it developed. And just like right after it peaked, it just started warming up. And it took about 9,000 years. And all of the ice sheets, all the glaciers, all the stuff that was covering Earth and keeping it in an Ice Age just basically went away. And Earth just blossomed into a version that we like. Yeah. And it became, you know, not terribly unlike what we're looking at now. There was a jump in temperatures that was, you know, kind of close-ish to today. And this was called the, I never know how to pronounce. It's a umla. Is it really? Yeah, I'm that's all it is. Yes. So all of our Nordic friends, the circle with the forward slash through or the O with the forward slash through, that's an umla, right? OK. I mean, I guess we call it the null set because it looks like a zero with a slash through it. So call it that. I mean, we don't really call it that, but that's what it looks like. Pronounce it like that. All right. What, what with the umla? No, the null set. No, I would know how to do that with the umla. I guess my best stab would be the Burling Allerud interstitial. I think you nailed it. All right. A lot more rain. We got to, you know, we achieved a sea level that's not what we have today, but about half of what we have today with that rain. Obviously, you're going to get a lot of plants. The woodlands are thriving. Animals are now are, you know, forest dwelling and walking alongside things like cave bears and woolly mammoths. And things are going pretty good. We have homo sapiens at this point or are the only humans that are around at this point. And they're like, they're loving life, man. They're saying, all right, we can travel a little bit more. And as we'll see, you know, kind of dabble, stick their toe in settling here and there. Yeah, this was actually right before this was the point when people from Eurasia migrated into North America. So this was the point where they were cut off. They couldn't go back. There's no going back. They were in North and South America now because the Bering Land Bridge was covered up by those rising sea levels, which turned into the Bering Sea. And this time. So remember, we're talking about this little period after the end of the ice age before the Y.D. comes along, where everything seems to be going smoothly for humans. This is where we started taking our first stabs at agriculture. We're just like, let's try something new. We just came out of an ice age. Let's just get as funky as we can with it. And we're going to basically take some of that energy in that time that we dedicate to hunting and gathering and put it into farming. I just made that word up, but let's call it that for now on. They're like, what is farming? They're like, you're doing it right now, buddy. I see over there picking weeds and tending to those wild plants. And that's basically the, you know, kind of, I guess, the argument for the beginning of agriculture at least, right? Yeah, we basically said, that's a good looking plant. Let's just try to make that one grow as well as we can. That's right. So things are going along swimmingly. People are not moving around as much. They enjoy sitting for the first time and things like that. And then all of a sudden the YD comes along and the glacial conditions return in the broad sense in a very quick way. I mean, how long did it take? Like, I mean, the whole thing was like a thousand years, but we reached kind of close to that last glacial maximum in about 500 years. Yeah, I think by a hundred years, it was really like in full swing. And then, yeah, 500 years is basically like the ice age is back. I wonder if they were like, hey, does anyone think it's getting colder? No, just keep farming and be quiet. Yeah, just keep planting those plants. We should also say Kyle helped us with this. And he said that the younger dryest came along and spoiled the party. That's truer than you would think, because right before this, in that bullying, all around interstitial was when we started making beer, too. So that got disrupted as well. We'd be so much drunker today. So another reason we would have wiped ourselves out in just one global bar fight, basically. Yeah. So this is this kicks off 1300 years of really, really cold weather. And then all of a sudden, it just stops and it it it comes along. It like happened starting about 100 years, 500 years into it. It was really basically back to ice age conditions in a lot of places. But when it stopped, it swung back to nice and humid, even faster. And there's actual ice cores from Greenland that show that Greenland in 10 years, the average temperature increased by 18 degrees Fahrenheit, 10 degrees Celsius. That is insane. And for comparison, so the global warming that's going on today that scientists are quite concerned about and thinking people as well. That's a rise of two degrees Fahrenheit, not 18 degrees Fahrenheit, two degrees Fahrenheit in about 20 decades. We're talking about 18 degree rise in one decade. That's how fast this thing warmed up. Yeah, that's super quick. And again, you know, whenever you talk about this kind of stuff, you got to zoom out and look at it from a sort of macro point of view. But yeah, that's super fast and got super hot and also super cold previously during the YDs, which was named, by the way, after a flower, the driest octapetala. Yeah, nailed it. And the odd thing about this flower and why they named the YDs after it is that it thrives in cold Arctic regions is one of these flowers that loves the ice, kind of the mountains of Scandinavia. And in the late 1800s, like the 1870s, Swedish scientists were studying clay deposits that they discovered. And they discovered this flower and they were like, this flower shouldn't be here between these layers of clay. It was deposited by melting glaciers, but like none of that makes any sense. No, because you've got clay from melting glaciers above it and clay from melting glaciers below this flower. And this flower thrives in temperatures where the glaciers are not melting at all. So it was a huge mystery. And then what made it even more mysterious is that it was confirmed by other clay deposits elsewhere in Scandinavia. So there was definitely something weird going on. And they named it Younger Dryas because there actually had been an older dryas before that was not nearly as much of a bizarre freak as the Younger Dryas was. That's right. So we got the OD, we got the YD. Should we take a break? Yeah, that sounds like a pretty good time for a break. Yeah. Yeah. All right. We'll be right back. Chuck and Josh. Stuff you should know. Hey, I'm Nora Jones, and I love playing music with people so much that my podcast called Playing Along is back. I sit down with musicians from all musical styles to play songs together in an intimate setting. Every episode is a little bit different, but it all involves music and conversation with some of my favorite musicians. Over the past two seasons, I've had special guests like Dave Grohl, Lavey, Rufus Wainwright, Remy Wolfe, Mark Rebier, Mavis Staples, really too many to name. And there's still so much more to come in this new season, including the powerful psychedelic duo Black Pumas, my old pal and longtime songwriting friend, Jesse Harris and legendary Lucinda Williams. Listen to Nora Jones is playing along on the I Heart Radio app, Apple podcasts or wherever you get your podcasts. Are there any pictures of you online? I'm not just talking about Google. I'm talking anywhere. Clearview scrapes together images from Facebook, from LinkedIn, from Venmo accounts. That database is now being used by police departments all across the country to match criminal suspect photos. And sometimes it makes mistakes. So in this one case, two of the search results that I think were in the top 10 of the search results were Michael Jordan, a picture of Michael Jordan. But cops are still using it to make arrests. Police, they are trusting this software to lead them to the right suspect. But you're not even being told that it was used, let alone given any of the details about how it works. This is not minority report. This is happening right now. People are getting arrested and doing actual time in jail after being picked out by a computer. I'm Dexter Thomas, host of Kill Switch, where every Wednesday we explain the right now of living in the future. You can turn off the computer, but do not let the computer turn you off. Listen to Kill Switch in the I Heart Radio app, Apple podcasts or wherever you get your podcasts. You know, the shade is always shady is right here. Season six of the podcast, reasonably shady with Giselle Bryan and Robin Dixon is here dropping every Monday. As two of the founding members of the Real Housewives Potomac, we're giving you all the laughs, drama and reality news you can handle. And you know we don't hold back. So come be reasonable or shady with us each and every Monday. I was going through a walk in my neighborhood out of the blue. I see this huge sign next to somebody's house. OK, the sign says my neighbor is a Karen. No way. I died laughing. I'm like, I have to know. You are lying. Humongous, y'all. They had some time on their hand. Listen to reasonably shady from the Black Effect podcast network on the I Heart Radio app, Apple podcast or wherever you get your podcast. So, Chuck, we've been talking like pretty big shots, pretty confident here, right? A couple of tough guys. Exactly. And the reason why we're doing this because of ice core samples. A lot from Greenland also from Antarctica and sedimentation from high altitude European lakes. That's why we're talking so tough right now. Yeah, and those are big deals. You can find out a lot from an ice core. You can find out like basically what's what it accumulated there, like stuff that the wind blew in there from other places. You know, they've got these little little bubbles in that ice and you can trace gases even that were present back then and compare to like other parts of the world at that time. And like, oh, we have these gases here. We have this sediment here. We have a distinct lack of pollen for this period here, which means like probably a lot of plant life was killed off and stuff like that. And then the lake stuff is super valuable too, right? Yeah, because constantly sediment is accumulating at the bottom of a lake and very similar stuff is getting trapped down there, like air bubbles, soot, pollen, all that stuff. And it just gets deposited year after year. And you can actually date that stuff. You can take a sample of the lake bottom and date that and then see what was going on around the lake at that time, too. And lakes are advantageous because they're all over the world. Ice shelves and glaciers are not all over the world. So you're limited from where you can take ice cores. And then also, lakes can last like thousands of years. Whereas if you're reading tree rings, you're reading maybe decades, maybe a century or two worth. A lake, it's going to give you way more than that. So it's pretty clever the way that they can take this stuff, not only figure out when this sediment deposit or this ice deposit was put down, but also what like a lack of pollen or what type of pollen means for like the world that large at the time. I just think that's pretty cool that humans are able to do that. And they don't seem to just be making this up. You know, a very niche, nerdy stuff. You should know t-shirt could just be lake bottom, greater than symbol tree ring. That's a super nerdy. I think that would actually offset the be dumb and happy one that you got generated. I think so. But just, you know, you walk around like Comic Con and somebody you'll say, I know exactly what you're doing, buddy. And they'll they'll just silently walk past you and give you the high five and the low five without stopping. Right. But it'll be a sort of a nerdy. They'll miss the high five. They won't be quite right. They'll try and fist bump you when you put up your hand or something. Or they lock fingers with you on the lo-fi. And you guys keep trying to go in different directions. It's that's got to be the worst. I thought the fist bump in the hand together was the worst. But that's pretty high five. And someone holds on and locks fingers, not what you're after. Yeah. So weird. Oh, goodness. I don't know why I think of Oprah Winfrey. When does she has she ever done that? I think she likes to raise people's hands like they just want a boxing match or something. All right. So we're settling into the YD. I mentioned earlier that the north northern hemisphere was one that was really affected the most, especially around the north Atlantic. The southern hemisphere, we'll talk about some weird abnormalities there as well. But these ice sheets advanced across the Arctic Seed, just like they did during the old LGM, the last glacial maximum. Is it glacial or glacial? Oh, I don't know. Depends on whether you say potato or potato. I guess so. The Rockies here would later be the United States expanded. The Alps expanded. They found very weird things like penguin like creatures in southern Italy. Like things were getting really out of whack again. And everyone back then was like WTF. Yeah. And the like, even if you weren't living in an ice over area, you know, basically due south of that was Tundra. Like so Western Europe, which is nice and verdant and lush right now, was Tundra at the time. You've got grasses, maybe a fox or two. If you're lucky and you're bored just looking around because it's not the most pleasant landscape to look at. I remember humans are running around at this time. I think we shrunk tremendously as a population down to maybe the highest estimate I saw was around 10 million people across the entire planet at this time. That sounds nice, actually. We kind of talk about Elba Room. But the all the plants and animals that had started to thrive in the middle in between the Ice Age and the YD, they died back and all the animals and plants that had died back during the interstodial period, they came roaring back. And they were like, we love the YD. We're happy again. Yeah, for sure. I mentioned the pollen retreating, being evidence of like, you know, the tree cover going away. And they found evidence of that and ice core once again. This is in the Hulu Cave in China. And it showed, you know, a drastic reduction in tree pollen, which, you know, basically you can infer that. Like, yeah, a lot of a lot of trees died out during this icy period. Right. And from that, you can also infer that there was probably less rain because trees help generate clouds and they also help keep the planet warm. So it was obviously a lot colder and a lot drier. That was the two characteristics of the YD. And then, like you said, the Southern Hemisphere experienced something radically different, right? So remember, Northern Europe is covered in ice again. It's tundra right below that. And then if you go down to Antarctica, they basically hand you like a lay and a Hawaiian shirt and like a Mai Tai. Yeah, it's so crazy when I was going through this stuff. That, to me, was like the big reveal. I mean, I'm a big dummy when it comes to this stuff. So I just figured that would have been even colder and even worse. But temperatures actually rose in the Southern Hemisphere. And a lot of the Southern Hemisphere became warmer and wetter. And the sea surface temperatures increased in the Caribbean and the tropical Pacific and the mountains of New Zealand saw warmer conditions. So it was like everything was kind of upside down all of a sudden. Yeah, but you also mentioned earlier that it didn't happen. There were weird pockets here there, which also goes to underscore how bizarre the Younger Dryas was. Like there's a basin around Venezuela and it actually had temperatures drop. So this is the Southern Hemisphere, right? It saw a temperature drop of three degrees Celsius, five and a half degrees Fahrenheit. And every time I see something like that, I'm like, so like that's not that big of a deal. Right. It turns out it is a really big deal. Even though to you, an average winter temperature of 55, going down to 50, doesn't sound all that bad. But climatologically speaking, any change in temperature, even by half degrees, has really huge weather consequences over, say, the course of a year. So in this case, dropping by three degrees Celsius or five and a half degrees Fahrenheit, it might not have seen that much temperature wise over an average winter, but it also opened up the door for way more freak weather. So they might have gone from like no blizzards whatsoever, maybe one blizzard a year to three blizzards a year. And that definitely impacts local conditions in the life there. So it makes a really big difference even when you see little changes to average temperatures. Yeah, for sure. There were likely some animal extinctions happening. You mentioned the amount of humans, which was at an, you know, probably at an all time high at this point, started going back lower and lower. Their available food was getting slimmer and slimmer. We mentioned they were dabbing their toe in the pond of kind of settling down a little bit and not hunting and gathering and traveling everywhere. And all of a sudden they had to pack it up and start moving around again to try and find food again. Yeah, and there's the evidence that the people, the human population contracted, meaning there was a lot of die off, shows up in archaeological sites like the Herensburg culture in present day Germany, Austria and Belgium. During the YD, the archaeological sites dropped by half compared to what they had been just before the YD, which suggests that there are a lot fewer people making a lot fewer camps or villages. And then also significantly in North America, this is when the very famous Clovis culture just disappears from the record. Clovis, we did a whole episode on the Clovis. Yeah, they used to pop up a bunch. Remember the whole Clovis first police and all that stuff? Yeah, man, it feels like a thousand years ago. It really does. But so this is when they disappeared. They don't think that the Clovis all just died off, but they think that these weather conditions and hardships for living basically disperse them. And they started forming the prototypes to the bands of Native Americans that we see today. Yeah, for sure. Another interesting thing is in, you know, sometimes in the times of trouble, there can be human advancement because you're struggling and need to think of better ideas on how to do what you're doing. And it seems like that might have happened with the hunting because the animals are more scarce, hunting is harder, the game is just not around. So this is where we saw at least one thing that we think might have been an advancement was the hariff point, H-A-R-I-F, which is basically a new and improved arrowhead came about. And they think it's probably because they were struggling and they needed to kill better. Yes. And it was quite an innovation because the arrowheads they were using before were made of dandelion heads. I know. And those, you know what? The animals loved them. They were like, shoot me again. Yeah, shoot one of those my way. I could use a laugh. Right. Um, and then also Chuck, it really helps that there were people dabbling in agriculture before the YD came along, because it seems to have given the people related to them a bit of a leg up. Like they didn't have to figure out agriculture from scratch under these conditions. So in pockets where there was vegetation and a decent amount of game, people did settle down again in those areas. There's a place called the Zagros region, which is in modern Iran. Um, which shows settlements that were basically probably not, um, just hunting camps, they were probably permanent or semi-permanent settlements. So people did like sit down where they could and, and set up shop. Um, and as a matter of fact, some people say, okay, people were kind of dabbling in agriculture before, but it was just dabbling. And in fact, that's that culture might not have been passed along. It is possible that the younger dryists did force humans to basically adopt agriculture, because again, remember conditions are so terrible that whatever leg up you, a human can give to this plant that you're going to eat later is, is invaluable. Um, so that's basically what agriculture is, is helping plants along to make them grow better. Yeah. And you know, it, that became a challenge in a lot of ways, not just because the ice, but they found once again in those ice deposits or the ice cores, they found air bubbles with, um, a noted, uh, decrease in concentration of CO2 in the atmosphere. Yeah. And so all of a sudden these wild cereals that are growing, their yields are going to be way down. And, uh, you know, they, they had some, you know, for the time, some fairly advanced, uh, agriculture burgeoning there, they were like pest control and like watering things, weeding things, transplanting things. The basics. Yeah. The very basics, but that's, you know, the very beginnings. And, uh, yeah, that this put a big sort of stop sign in front of all of that. Yeah. Like imagine being the guy who is watching the other guy pour water out of his gazelle flask onto like, uh, like a little, yeah, like some wheat. Yeah. What are you doing? And they, they'd say, just, just watch. Just give me a couple of thousand years and you're going to be blown away. Yeah. You want this water to be beer one day, fella? Exactly. Let me pour it on this, uh, this grain. And then it magically turns into beer. Oh man. Shall we take another break? I think we shall, Chuck. Hey, I'm Nora Jones and I love playing music with people so much that my podcast called playing along is back. I sit down with musicians from all musical styles to play songs together in an intimate setting. Every episode's a little bit different, but it all involves music and conversation with some of my favorite musicians. Over the past two seasons, I've had special guests like Dave Grohl, Lavey, Rufus Wainwright, Remy Wolfe, Mark Rebier, Mavis Staples, really too many to name. And there's still so much more to come in this new season, including the powerful psychedelic duo, Black Pumas, my old pal and long time songwriting friend, Jesse Harris and the legendary Lucinda Williams. Listen to Nora Jones is playing along on the I Heart Radio app, Apple podcasts, or wherever you get your podcasts. Are there any pictures of you online? I'm not just talking about Google. I'm talking anywhere. Clearview scrapes together images from Facebook, from LinkedIn, from Venmo accounts. That database is now being used by police departments all across the country to match criminal suspect photos. And sometimes it makes mistakes. So in this one case, two of the search results that are, I think we're in the top 10, the search results were Michael Jordan, a picture of Michael Jordan, but cops are still using it to make arrests. Police, they are trusting this software to lead them to the right suspects. But you're not even being told that it was used, let alone given any of the details about how it works. This is not minority report. This is happening right now. People are getting arrested and doing actual time in jail after being picked out by a computer. I'm Dexter Thomas, host of Kill Switch, where every Wednesday we explain the right now of living in the future. You can turn off the computer, but do not let the computer turn you off. Listen to Kill Switch in the iHeart radio app, Apple Podcasts or wherever you get your podcasts. It's okay not to be okay sometimes and be able to build strength and love within each other. Thanksgiving isn't just about food. It's a day for us to show up for one another. I'm Elliot Connie, host of the podcast Family Therapy, a series where real families come together to heal and find hope. What would be a clue that we'd be like? I've gotten lots of text messages from him. This one's from a little bit better of a version of him. Because he's feeding himself well, it's always a concern. Like, are you eating well? He's actually an amazing cook. There was this one time where we had neighbors and I saved their dog and I ended up inviting them over for food. And that was like one of my proudest moments. This is Family Therapy, real families, real stories on a journey to heal together. Listen to season two of Family Therapy every Wednesday on the Black Effect Podcast Network, iHeart Radio App, Apple Podcast, or wherever you get your podcasts. All right, we should talk a second about something called solar insulation, not insulation, insulation with a no. And this is how much solar warmth reaches the earth's upper atmosphere. And the basic pattern of warming the globe is driven by this. And the Younger Dryas is definitely like this weird, exceptional pocket that stands out. And because of this, everyone that nerds out on this kind of stuff was like, well, we got to figure this out. I mean, why did this happen? And they have emerged with four main hypotheses. The one that has the most traction we're going to start with is the melt water interrupting thermohaline circulation. And that sounds very sort of like a sciencey nerdy and like guys, I hope you explain this, but it's really very simple. It is. Is that a bunch of water disturbed the cycle of the warming cycle of the ocean very, very quickly. Yeah, specifically in the North Atlantic, which has this thing that you mentioned, the thermohaline circulation, which is where warm water, warm by surface air on top of the ocean falls down into the deep water. And as it does it, it displaces the cold water, which comes up to the top and gets warmed itself. Then it sinks and the cycle just keeps going on and on, right? And this is how warmth is delivered to the north, the northern hemisphere, right? It moves northward, so the warmer seawater is always moving toward the north. So it's delivering warmth. And at the same time that cold water up wells in the southern hemisphere, so it delivers cold to the southern hemisphere, which is why under normal conditions with the thermohaline circulation, the Antarctica is cold. And comparatively speaking, the northern hemisphere is warmer. That's right. All right. So park that in your in your brain and then understand that North America at the time had this huge 700 mile by 200 mile lake called Lake Agassiz, I guess. Sure. Agassiz, if you're an Andre Agassiz fan. It developed as the Laurentide ice sheet and extended down to the Great Plains and blocked the Great Lakes and all the rivers that were flowing there backed up and it formed this big natural reservoir that was 700 by 200 miles big. And this theory holds the meltwater theory holds that as that last glacial maximum warm things up, that ice sheet retreated, the block passage to those Great Lakes opened up and all of a sudden billions and billions of gallons of freshwater make its way down to the North Atlantic. They think a similar sort of thing happened in the in the Nordic region. But you're like, all right, so that makes sense. But was this water like super cold or something? It was cold. But the main thing it did was desalinate that that upper ocean water, right? Yeah. And so fresh water is less dense than seawater. And so a bunch of fresh water mixed in with seawater makes it less dense than it normally would be. And it needs to be dense to fall down to the deep ocean, which makes the other deeper water come back up, right? So that means that the thermohaline circulation is interrupted. And if you have an interruption in the thermohaline circulation, it just stops moving like that. You would expect to see the northern hemisphere get cold because there's warmth is not being delivered there any longer. You'd also expect to see Antarctica warm up because that cold deep ocean water is not welling up around the very southern, southern hemisphere. And that's exactly what you see with the younger drys. It's a really beautiful, elegant explanation that I think was hypothesized in 1982. And up until very, very recently, you were a fringy nut. If you believed anything besides that as the explanation for where the younger drys came from. Yeah. I mean, it makes sense to me, but that's why I love science, is people keep poking around in the fringe nut. Maybe one day is proven somewhat right. And that, well, I still think that the melt water is probably the reason why. But one of the other hypotheses is the impact hypothesis. And that is, like you said, was pretty controversial until more recently. It has gained a little bit of traction because some things do kind of add up. But the idea here is that a meteorite or a comet or something impacted the earth, maybe an air burst, even, and that released a thermal pulse that kind of set the world on fire almost like all these massive wildfires across all the continents, the air spilled with soot. It's blocking sunlight. And in fact, it's there's so much that there's atmospheric dust such that you reduce solar radiation. And all of a sudden you have what's called an impact winter or, you know, kind of like a like a new the idea of a nuclear winter. Yeah, basically the same exact result, but just there was different things that got us there. Right. So there's evidence for this that most people point to is like, this is pretty good evidence. There's something called a black mat, which is a layer of carbon matter that seems to be a soot deposit that you find all over North America and in parts of Europe. And all that suggests that there were wildfires going on on different continents at the same time, which would suggest like some sort of massive comet or meteorite bursting and setting off this thermal pulse. So the fact that those things coincide on two different continents with the onset of the younger dry us has definitely made the the impact hypothesis much more popular than it was before. One thing detracting from it that probably makes some legitimate scientists wary of embracing it publicly right now is the writer in science contrarian Graham Hancock latched on to the impact hypothesis, because he has this theory, I guess you could call it that, that there was an ancient apocalypse around the time that the younger dry has happened that wiped out massively advanced civilizations that we don't even know it really existed and reset humanity. And then we had to rebuild from there. And there's not a lot of evidence, if any, for this stuff. It's really, really fascinating. But the evidence we do have, the scientific evidence we do have doesn't set that up. But anyway, he basically said, see this impact hypothesis supports my idea that there was an ancient apocalypse. And scientists tend not to agree with Graham Hancock much. Yeah. And the other thing, there's a couple of more sort of smaller points that might support this. One is there was a platinum spike in South Africa that proceeded the Y.D. and in some other places. And platinum is, you know, a lot of time within meteorites. So maybe some support there. And also sometimes people kind of combine the first one and say, maybe there was an impact combined with this meltwater thing. So there was a low atmospheric explosion over North America. And that's what released all this meltwater all over the place. Yeah, which makes sense. It's basically like handing an olive branch from one hypothesizer to another, you know, let's work together. Yeah, let's go get a drink and just settle it. Also, as an aside for, remember our goblecky tepe episode? Oh, yeah. It's been a while. I don't remember exactly how to pronounce it. We talked about how there was this guy who also kind of fringely concluded that some astronomical engravings at the site recorded the comet or the meteorite burst that happened at this time, which is kind of cool. But again, there's not a lot of evidence to support it. Moving on, there's a couple of other explanations that don't have nearly as much traction, but they do make sense. One is a supernova explosion. Supposedly a star went supernova in the Vela constellation at the right time that could have affected Earth by burning away its ozone layer, which would cool the upper stratosphere, which is the second most layer above Earth, which would prevent it from holding much water vapor. Water vapor is a greenhouse gas and without a very strong greenhouse gas in the atmosphere, heat would just go out into space much more easily from Earth and it would get cooler as a result. The problem with this one that I have is wouldn't that happen all over the planet if the ozone layer was burned away by a supernova? I think so. So I'm going to I'm going to toss that one. OK. Yeah, nailed it. The last one is another sort of example where the sun is blotted out, so there's a massive drop in temperature very quickly. But this time it is because of volcano erupted, a massive volcano. This is the Locker C volcano, not CEA, or I'm sorry, SEA, but SEE because we all know that Germany doesn't have any water, right? Well, it's landlocked, yes. Yeah, but this is a German volcano. Of course, we're kidding. That's a reference to an older episode. We know all about the Black Sea to hold your emails. But this volcano, it was definitely a mega eruption, it spewed 6.3. I mean, what is that even trillion? What is that? That's a cubic kilometers. So three million cubic kilometers. No, 6.3 cubic kilometers to the third power, though. No, so that that's what makes it cubic. So if you took a kilometer of land. Oh, yeah, yeah, yeah. And you made it square and you did that 6.3 times. And then you also made it a kilometer tall, a cube. That's 6.3 kilometers on each side. Yeah, just of magma got released from that volcano. It was a massive eruption. Yeah, I just outed myself in a mathematical way. Well, finally, you did. I'm the one who does it all the time. Well, comparatively speaking, Mount St. Helens released one cubic kilometer. Vesuvius was three and this was 6.3. So the other interesting thing about this one is volcanoes can produce platinum or at least, you know, part of like groups of platinum metals. And that could account for that spike we talked about in South Africa. Yes. And so the volcanic eruption hypothesizers frequently say, hey, how about this? A volcano erupted and attracted a comet that blew up over North America, which kicked off the melting of the ice caps, which caused the thermohaline circulation problem. Yeah. And then the supernova person is like, what about me? And they're like, sorry, you're not invited. Josh said you were dismissed. Exactly. All right. So that was the YDs. I guess we could talk a little bit about what happened afterward. Afterward is where we are, the Holocene period. And that was when the climate finally worked itself out. That pendulum stopped swinging and things started warming up and stabilizing. And, you know, people started thriving again. The animals came out, the birds started chirping, the bees started pollinating. And and we and it led to, you know, the not the modern modern era, but just, you know, what we know now is planet Earth. Yeah. The beginnings of our era all find its roots in this this time. Like this is where agriculture develops. This is where civilization first developed. Writing came along a few thousand years later. I mean, all of this happened in a really short period of time. Like essentially everything that has to do with like human civilization began in the 10,000 years immediately following the Younger Dryas. Yeah. I mean, the current the current shape of our planet happened after the Younger Dryas, like the way the coastlines were shaped. Mentioned the Rockies and the Alps, you know, those those mountain ranges all over the world, even they I was about to say took their final shape. That of course, that's not true, but took the shape that we know and love today. Yeah. And that's actually one reason why it's difficult to track what humans were doing during the Younger Dryas, because the the settlements that they had that were closer to the coastline then are now under hundreds of feet of ocean water. And are probably just totally destroyed. So we lost a lot of archaeological sites because of that sea level rise. But it was a trade off because again, we have writing. Yeah, that's right. And those wild cereals that we talked about that we're having such a hard time, you know, became Captain Crunch. Yeah. And really, is there anything more you need to prove that humans have reached peak civilization than that? I don't think so. OK, well, I guess that's it for the Y.D., right, Chuck? That's it for now. I mean, who knows what's ahead? Well, but and because Chuck said, who knows what's ahead? Truly, it's time for Listener Mail. This is called Birthmark episode, because we I think that might have been a selector. Maybe Patrick just listened to it again. I think so. That's what happened. Hey, guys, listen to that episode again recently because I have a birthmark that makes me perpetually look like I have a black eye on a regular regular basis. Someone will ask me some variation of like, who punched you? What happened to your face? I used to enjoy giving a clever story as a way to mess with them, like getting kicked out of an club or squaring off with a bear. But I started to feel bad for lying even to my friends, even if only for a minute. So now I usually just take the boring route and explain that it's a birthmark. It's just subtle enough that friends can go years without noticing it even. Well, but once it's brought to their attention, they can't unsee it. Many don't believe me when I tell them it's just a birthmark and they think I'm trying to cover something up. My mom even told me that she was interrogated when I was a child by doctors. And we get dirty looks from other parents when they notice a mark on my face. And I feel bad that her experience of my birthmark has never been as fun as mine. Anyway, ever since my wife, Christine, introduced me to your show about nine years ago, the stuff you should know has been a staple for us during house tours and road trips. Your chemistry together is very comforting. And we especially like hearing Josh make Chuck laugh. Do it right now. Um, hot potato. That actually worked. I was like, I'm going to have to take a laugh here. But you got me. Awesome. Keep up the great work, guys. Thanks for making the two of us smile again and again and again. We've made them smile three times. All the best from Troutdale, Oregon. That is Patrick Burton. Awesome. Patrick, thank you for that. Patrick and his wife, Christine, right? Yep. So thanks to you both. And Patrick, I have to say, if you're going to have a birthmark that's not in the shape of Abraham Lincoln, the place that you have it is about as cool as it can be. I agree. If you want to be like Patrick and Christine and let us know how long you've been listening to us and what you think. Hopefully it's generally positive. You can send us an email to send it off to [email protected]. Stuff you should know is a production of I Heart Radio. For more podcasts, My Heart Radio, visit the I Heart Radio app. Apple podcasts are wherever you listen to your favorite shows. Michael Lewis here. My bestselling book, The Big Short, tells the story of the buildup and birth of the U.S. housing market back in 2008. A decade ago, The Big Short was made into an Academy Award-winning movie. And now I'm bringing it to you for the first time as an audiobook narrated by Euras Truly. The Big Short story, what it means to bet against the market and who really pays for an unchecked financial system. Is as relevant today as it's ever been. Get The Big Short now at hushkin.fm/audiobooks or wherever audiobooks are sold. Join me, Danny Trejo, in Nocturnal Tales from the Shadows. An anthology of modern-day horror stories inspired by the legends and lore of Latin America. Listen to Nocturnal Tales from the Shadows on the I Heart Radio app, Apple Podcast or wherever you get your podcasts. Bells, jingle bells, jingle all the way. Yo, yo, yo, yo, yo, can we get things given first? I'm hungry. What's up, y'all? It's Kadeen. And DeVal, the host of the Ellis Ever After podcast. 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