What’s the largest asteroid impact in Earth’s history?

00:00:08
Speaker 1: Daniel. It's great to be talking to you today. So now I would love for you to go ahead and reassure me that today we're not going to be talking about how scary and dangerous the universe is.

00:00:21
Speaker 2: Oh no, no, not at all. Well, I mean maybe a little bit.

00:00:24
Speaker 1: Uh, Daniel, that is clearly hedging. I'm gonna need more clarity.

00:00:29
Speaker 2: I mean, we're only going to talk about scary and dangerous family destroying things that already happened in.

00:00:35
Speaker 1: The past because we have some way to prevent these scary and dangerous things from happening in the future, like to my children. Right, no comment, dude, not okay, totally, totally, not okay.

00:00:52
Speaker 2: You got to embrace the danger, Kelly. That's where the thrill is.

00:00:55
Speaker 1: I I guess I'm pushing through one way or another. So let's do this just another show my kids won't listen to.

00:01:19
Speaker 3: Hi.

00:01:19
Speaker 2: I'm Daniel, I'm a particle physicist and a professor at UC Irvine, and I'm looking forward to the destruction of the Earth.

00:01:26
Speaker 1: I'm Kelly Waitersmith, adjunct faculty at Rice University, and I'm looking forward to yet another episode filled with existential dread.

00:01:37
Speaker 2: You know in those moments as the Earth is being obliterated by some huge impactor, We're going to learn a lot about how the Earth is put together and what's inside of it. And as all those insides come to the outsides.

00:01:49
Speaker 1: You know, I'm going to hope that in that moment we all stop worrying about the details and we just hug our kids and our dogs and stuff. But I'm sure the physicists we'll still be collecting data, and the economists will be quantifying something, and anyway, well.

00:02:05
Speaker 2: We are all still live and wondering about the universe. And so welcome to the podcast Daniel and Jorge Explain the Universe, a production of iHeartRadio in which we do our best to understand the nature of the universe before it comes crashing down on us. We try to cast our minds out into the deepest, darkest reaches of space and understand what's out there, how does it all work. We look back into the history of the universe to understand where it all came from, how it all works, and how we got to be where we are. Jorge can't be with us today, but I'm very glad to have with us. Kelly. Kelly, thanks for joining us on another adventure of dangerous history of the universe.

00:02:44
Speaker 1: Thanks for having me. Despite what it might sound like, I really do enjoy these episodes.

00:02:51
Speaker 2: And there is a lot of danger out there in the universe. If you cast your telescopes up to the Moon, for example, you see that the surface is riddled with craters. It looks like it's survived a drive by asteroiding. And if you look even further out into the Solar System, you can see crazy things like comets smashing into Jupiter, creating fireballs the size of Earth. All this kind of stuff seems to be happening all over the Solar System. It's a dangerous place, epic and that might make you wonder, of course, how safe is our home here? Is the plan be strategy for a planet Earth super important? Do we need to scramble to get off of Earth before something comes and obliterates us. One way to answer that question is to think about our cosmic history. Of course, we'd like to know what might be hitting us in the future, but the best way to learn about that might be to think about things that have already hit us in the past.

00:03:44
Speaker 1: Are you going to be making me a question? The conclusions from my book that maybe we do need that Plan B and we need to start today because our demise is imminence.

00:03:56
Speaker 2: Maybe, or you could also look at this history and say, hey, we survived all this stuff, so maybe it's not such a big deal.

00:04:02
Speaker 1: Right, all right, Well, let's see where this goes.

00:04:06
Speaker 2: And so today on the podcast, we're going to be diving deep into the history of Earth to answer the question what is the largest asteroid impact in Earth's history?

00:04:20
Speaker 1: You know who has a big impact. Your listeners, Let's hear what they have to say.

00:04:29
Speaker 2: Thanks very much to everybody who volunteers for this audience participation segment of the podcast. We really love hearing your voices. It helps us calibrate the level of the podcast. Plus, we love you guys. We want to hear your voices and we hope you enjoy hearing your own voice on the podcast. If you'd like to play for a future episode, don't be shy. Write to me two questions at Danielandjorge dot com. Here's what listeners had to say. Wasn't just the asteroid that made the dinosaurs extinct? Almost meaning?

00:05:00
Speaker 4: Was it thea the planetoid that theoretically smashed into the Earth and kind of blew them both apart and became the Moon. I saw a model recently that looked so beautiful of kind of this orange fluid, two spheres banging into each other, and then the Moon forming, So maybe it was that one.

00:05:21
Speaker 3: I think that there's remnants of an ancient impact crater in Europe somewhere, or maybe South America.

00:05:27
Speaker 2: I can't really remember.

00:05:29
Speaker 3: From memory. There was a very large asteroid impact in South America somewhere that closed one of the dinosaur extinctions, but I can't remember what its name is. Well, alternatively, could the moon the collision that created the Moon be the largest impact that the Earth has they've experienced. I don't know whether that counts as an asteroid, but maybe the first one.

00:05:52
Speaker 5: That comes to mind disaster that killed the dinosaurs, though I guess that was only like sixty five million years ago. Since the Earth has been around for I think billions of years are probably many more, much larger than that earlier on. I guess another idea might be whatever it was that hit the early proto Earth and split off into the Moon.

00:06:09
Speaker 6: Well, the extinction event of the dinosaurs comes to mind up top, but probably there was a larger collision when the planet was still pretty squishy. Probably there was a larger one there, my best guess.

00:06:23
Speaker 1: So one thing that I thought was interesting about the responses is that I think there was a bit of reticence to answer because folks weren't certain that they had the difference between asteroids, meteors, comets meteorites clear. Should we quickly go over like which ones and clarify that we're specifically talking about asteroids today or do you think we don't need to go over that.

00:06:45
Speaker 2: No, I'm always down for exploring the ridiculous naming systems in physics.

00:06:52
Speaker 1: Or is today's episode just like giant hunks of stuff and we're being general?

00:06:57
Speaker 2: I mean, from a physics point of view, it doesn't really matter. It's giant hunks of stuff hurtling themselves towards the Earth that created huge explosions and left marks on the Earth's surface. But it does kind of matter where those things came from if you want to think about our future prospects and whether, for example, your children will survive.

00:07:12
Speaker 1: And I do care about that because I'm not a physicist, And so what's the difference between an asteroid, a comet.

00:07:20
Speaker 2: And a meteor yeah, great question. So an asteroid is basically a small rock that orbits the Sun. These things are smaller than a planet if they're like bigger than the pebble sized objects that are called medioroids. So asteroids are bigger than meteoroids, but smaller than planets. And it's also the distinction that planets have to like clear the path they're in. So you can have like a bunch of asteroids in like a ring around the Sun and that's not an issue. But nothing in there can basically be a planet, even if it's as big as a planet. So there's a complicated distinction there between like planets, dwarf planets, asteroids and meteoroids. And then of course there's comets.

00:08:00
Speaker 1: Okay, but it's mostly all just a matter of size.

00:08:02
Speaker 2: It's mostly a matter of size. Comets actually come from a different place that come from deeper in their Solar system. There's either the Kuiper Belt or the Ort Cloud for really distant stuff, and we'll talk about that a little bit. So that's asteroids and meteoroids and comets. Those are all things out in the Solar System. A meteor is something that's burning up in our night sky, something that hits us, and so that can be an asteroid or a comet or a little bit of alien space junk or whatever. So meteor is basically when it hits the Earth, asteroid, meteoroid in comet is when it's still out there in space.

00:08:36
Speaker 1: Got it, Okay? And so the listeners were very interested or very aware of the extinction events where an asteroid wiped out the dinosaurs. And then there was another person who wanted to know if when the early Earth got hit and the Moon split off, does maybe that count? Yeah, the listeners are pretty darn well informed.

00:08:56
Speaker 2: I'd say it's almost like they're listening to an awesome podcast regularly that teaches them all about the Solar System and the universe. Congrats and they pass the exam. But you're right that it is important to understand, like what's out there in the Solar System, where is this stuff coming from? What are the sizes we expect for things that are raining down on the Earth this death from above?

00:09:20
Speaker 1: Okay, So we've done like an overview of definitions. Let's jump into where asteroids come from and give a little bit more background about where you would find asteroids in particular, and.

00:09:32
Speaker 2: Go so something that you don't often realize when you look up at the night sky is you mostly see stars and planets, and you think about the Solar System in terms of, you know, like the Sun and the planets and maybe a couple of moons here or there. But the Solar System is much much dirtier than that. You know, there's a whole spectrum of chunks of stuff, from the Sun down to planets, down to moons, down to much smaller rocks. And as the stuff gets smaller, becomes much more numerous. So you've like obviously one Sun, a few planets, dozens of moons, But when you get to smaller chunks of stuff, asteroids and meteoroids and all that stuff, there's zillions and billions and even trillions of these things. But of course they're not luminous, right, They don't glow, and they don't reflect as much light because they're small, so you don't mostly see them in the night sky. They're mostly invisible. So the picture I want to paint in your mind is space being filled basically with dark rocks.

00:10:30
Speaker 1: Wait, so I have an important question. Yeah, So in Star Wars, this is how all important questions start in Star Wars, when they're like trying to navigate around rocks and space. There's just like they're everywhere and you can't get around them. If you were out in space and you were to stand on like one chunk of something, would you be able to see other chunks of stuff nearby? Or even though there's lots of them, are they still like pretty darn spread out or is it like Star Wars.

00:10:58
Speaker 2: No, it's a great question. It's not like Star Wars. It turns out Star Wars not a documentary, not a reliable way to plan your space mission.

00:11:09
Speaker 1: Who you got to know? That would have been embarrassing to say that public.

00:11:13
Speaker 2: But no, these rocks are pretty big. But they're also very far apart. Because space is vast, especially as you get out into the further reaches of the Solar System, the amount of space between these planets gets enormous, right, The volume of the sphere goes as the radius cube, and so if you're like another million miles away from the Sun, then you create a volume of space which is much much bigger than everything inside of it. And so even though there are lots and lots of asteroids out there, remnants from the formation of the Solar System that didn't pull together into planets or were disturbed by the gravity of Jupiter, for example, to prevent them from coalescing. They're far enough apart that you can't really have that's sort of like exciting space dodgem game.

00:12:00
Speaker 1: Well, you've dashed a lot of Star Wars related dreams today, but it's important to know, so, all right, So where do you find most.

00:12:07
Speaker 2: Of these So most of these things are in the asteroid belt, this region between Mars and Jupiter. And that's no accident. You know, as the Solar System is forming, it clumps together, mostly into the Sun and then into the planets, and planets form when you have like a seed of a heavy object, something that can pull stuff together and generate its own gravitational well, rather than just getting sucked into the Sun. But because Jupiter became so big, it's gravity was strong enough that it disrupted the formation of other stuff. And so that's why, for example, these asteroids near Mars Jupiter, even though they've been around for billions of years, they haven't like gradually coalesced into one big object. There's lots and lots of them over there.

00:12:49
Speaker 1: Oh, it's kind of fun to imagine what it would have been like to have another planet out there. It's like Jupiter.

00:12:54
Speaker 2: Another way you can see the effect of Jupiter on these asteroids is that there's a bunch of astrailids in orbit with Jupiter. If you draw an ellipse for where Jupiter goes around the Sun, it's not actually totally empty. There's a whole cluster of asteroids that are leading Jupiter and another cluster that are following Jupiter. They're called the Greeks and the Trojans. These two like different camps of asteroids.

00:13:17
Speaker 1: So I thought that planets were supposed to clear their orbits. Does that okay?

00:13:22
Speaker 2: All right?

00:13:23
Speaker 1: But Jupiter is huge, so all right, go on.

00:13:27
Speaker 2: So if you were like a lawyer for Pluto, you might raise this objection and say, hey, folks, you've been inconsistent here because planets are supposed to clear their orbit. But you know, when planets get big enough, then they can actually collect asteroids in these lagrange points, these points where the Sun and Jupiter's gravity balances out in a way that there's like a little gravitational well there for asteroids to collect in. But it's super cool. We're actually sending a mission to go visit these Trojans pretty soon be a lot of fun.

00:13:55
Speaker 1: Wait your what.

00:13:56
Speaker 2: We have a mission that's going to go visit the asteroid belt and one of these trojans.

00:14:00
Speaker 1: Ooh, that's exciting.

00:14:02
Speaker 2: Yeah, we had a whole podcast episode about it, Me and you, so check that one out if you're curious about it. But even though you imagine this space to be filled with rocks, and some of these are pretty big, like Series is a whole dwarf planet in this region. It's like nine hundred kilometers in diameter, So that's pretty big. I mean, it's like a tenth or thirteenth of the radius of Earth. That's the biggest thing out there in the asteroid belt. But after that it pretty much falls off. Like half of the mass of the asteroid Belt is in just four big Mama asteroids. After that, it's a bunch of smaller stuff.

00:14:35
Speaker 1: And those big Mama asteroids are stay input.

00:14:38
Speaker 2: I hope mostly they stay input. NaSTA does a really good job of tracking these folks and thinking about their trajectory. They can predict them out to about one hundred years from now. After that, it's too chaotic with all the influence from Jupiter and Saturn and the other little bits of the asteroid belt for them to reliably predict where they're going to be. But mostly they know where all the big ones are and they know they're not going to hit us in the next one hundred years.

00:15:02
Speaker 1: All right, all right, that's that certainty that I can handle. I'll sleep tonight, all right. So, so half of the mass is in those four objects, and how is the rest of the mass distributed?

00:15:13
Speaker 2: So after that it's lots of tiny little ones. And you know, it used to be much more. It used to be that the asteroid belt had like one hundred or a thousand times as much mass as it does. But when it's so dense over there, they will eventually bump into each other or even just pull on each other gravitationally and fall out of orbit and then plummet into the Sun. So something like ninety nine point ninety percent of the mass of the asteroid belt is gone. It was lost in the first one hundred million years of the Solar System. And what's left is a bunch of smaller asteroids. But even if you add it all up together, it's not even that much stuff. It's like four or five percent the mass of the Moon. If you like gathered it all together into one big ball.

00:15:54
Speaker 1: So do we need to worry about like so you said most of it has already fallen into the Sun or presumably fallen into Jupiter or something. Is the rest of it? Something like if voyager, you know, was going out past Jupiter, did we have to worry about it running into that stuff? Or there's just not that much of it out there?

00:16:09
Speaker 2: There's not that much of it out there. Yeah, if you pointed a spaceship through the asteroid belt, you'd have a very small chance of hitting anything.

00:16:15
Speaker 1: Nice. That's good to hear.

00:16:18
Speaker 2: Yeah, so you can put your kids on that spaceship and send amount of space without worrying about it.

00:16:22
Speaker 1: Kelly, No, No, my kids are staying here. I wrote a whole book on why this is a bad idea, four years of my life. My kids are staying here unless they want to go, and then I probably won't stop. Okay, let's take a break. So we've talked about the asteroid belt between Mars and Jupiter. There are other clumps of death from above, and we'll get to that after the break, all right, So, Daniel, where else are these clumps of death? Where else could they be coming from if they're going to be heading towards Earth.

00:17:10
Speaker 2: So the asteroids are not really something to worry about. We know where most of the big ones are, as we said, and we know where they're going to be. The more dangerous things are further out in the Solar system, out in the Kuiper Belt, like past Neptune, like between thirty and fifty AU, is a bunch of frozen ice cubes, essentially out past the snow line where the Sun is not powerful enough to vaporize. Ice can still be a big factor in the formation of clumps of stuff and also planets. Right, That's why we call Neptune and Urinus the ice giants. So out there in the Kuiper Belt, they're basically a bunch of big frozen snowballs, and sometimes some of them fall towards the center of the Solar system, and those are comets because as they burn their way towards the Sun, the Sun is then boiling stuff off of them, making that tail.

00:17:57
Speaker 1: And you maybe already said this, and I guess I just didn't understand. What, why are we more at risk from stuff in the Kuiper Belt than the asteroid belt, which is closer is there movement just more chaotic.

00:18:07
Speaker 2: Well, for two reasons. One is they come from further out, so that by the time they make it into our inner neighborhood of the Solar System, they're moving faster, like they've fallen further into a gravity well. And velocity is important because the faster you're moving when you hit the Earth, the more energy you're depositing, the more the seismic waves, the more stuff you toss up into the atmosphere. Velocity does matter. The other reason is that these things are harder to study. They're further away, so they're harder to spot, and they're more erratic. They're more susceptible to like passing stars that give them a little gentle tug and nudge them in towards the center of the Solar System. And there's so many of them out there that we can't possibly track all of them, so they're harder to spot and higher speeds.

00:18:50
Speaker 1: I don't like it all.

00:18:52
Speaker 2: Right, Well, then you're definitely not going to like. The Org cloud, even further away from the Sun is a theoretical cloud of basically icy many planets. We think there might be trillions of objects in there that are more than a kilometer wide, and maybe even billions that are twenty kilometers wide. You said theoretical, Yes, theoretical.

00:19:12
Speaker 1: I had assumed we knew this about the Ork Cloud already. This is just like stuff we think. I mean, I guess it makes sense. It's really far away, but we're we just think it's out there. We're not sure.

00:19:21
Speaker 2: We think the Orc Cloud is out there. It makes sense, it's part of all of our simulations. It's been predicted, but we've never actually seen something in the Ork Cloud because it is super duper far away. These things are like one to three light ears from the Sun.

00:19:37
Speaker 1: But it's on a bunch of the illustrations I've seen.

00:19:41
Speaker 2: Artists' conceptions. Oh my gosh, I know. No, this is basically an interstellar space. It's not really part of the heliosphere or the Solar system. But we do think it's part of the gravitational system of the Sun, and there's a lot of stuff out there. Theoretically, it's much further out than like even where Voyager one has gone, and it's so far away, and these things are pretty small, so it's hard to spot them directly.

00:20:04
Speaker 1: Well, Voyager one gets there before it runs out of power.

00:20:08
Speaker 2: It's going to take like three hundred years for Voyager one to get there, and it basically ran out of power. Recently, I heard that they stopped hearing from it, so we already know the end of that story.

00:20:18
Speaker 1: Oh oh, that's really sad. I can't believe I missed that. Yes, Christ in Peace one.

00:20:23
Speaker 2: Exactly, or floating piece or whatever you say out there in space. The Ork Cloud is theoretical. We're fairly confident it's there. We see indirections, and also we think it's the source of the longer period comets. Because these things are so far away, they take a long time to make it into the Inner Solar System and maybe impact on a juicy Inner Solar System planet or not. And so the shorter period comets probably come from the Kuiper Belt, and the longer period comets with even more mass and even more velocity come from the Org Cloud.

00:20:56
Speaker 1: Have we seen something come closer to us that we think came from ort cloud.

00:21:00
Speaker 2: Well, we've definitely seen a lot of long period comets, these comments that take centuries sometimes to orbit the Solar System, and so we think that they originated from the Ork Cloud. So yeah, we think those things are visitors from the Ork Cloud. And that's one reason why people are excited to like go sample comets while they're sending probes out there to grab bits of comments to see, like what is it like out there in the Orc cloud. Be awesome to get a sample of the Ork cloud that visited the Inner Solar System.

00:21:27
Speaker 1: Okay, so we've talked about where these things reside. Let's talk a little bit more about size. So like, if something that's a meter in diameter comes at us, that's not a problem, right, that's going to burn up.

00:21:44
Speaker 2: That's not a problem. That's actually kind of awesome. Yeah, it makes really nice streak in the sky. It doesn't really do any damage. And also it happens all the time. You know, space, as we said, is filled with dark rocks. Is not just the asteroids that we've cataloged in the asteroid belt. There's rocks out there all over the place, just floating free, tugged by Jupiter here and there. And that's why we see meteor showers. Right, Every meteor shower are a bunch of rocks hitting the Earth. Fortunately, our atmosphere is dense enough to act like a big pillow, and so when they hit the atmosphere, there's friction, they heat up and then they burn up before they hit the ground. And so stuff that's less than a meter in size, it happens all the time.

00:22:23
Speaker 1: Yeah, a big slammable pillow.

00:22:24
Speaker 2: You know.

00:22:25
Speaker 1: I was when I was researching the spacebook, and we were looking at companies that had sort of like out there ways of planning to make money on space stuff. There was a company that was pitching that they could make you essentially like asteroid meteor shower sorts of things by like sending masks to space and then having it come down at a certain time, and that they could like determine the colors that it would be. Wow, so like, you know, the most epic birthday present, like a pink meteor shower for your Kinsania.

00:22:59
Speaker 2: But anyway, that sounds like there's no way that could go wrong. Yeah, absolutely, that doesn't sound dangerous at all.

00:23:07
Speaker 1: No, No, it's great, it's great. Okay, all right, so we've got a meter and it's beautiful. When does it start becoming less beautiful and more scary?

00:23:18
Speaker 2: Yeah, So there's this trade off. As they get larger, they get more dangerous, and fortunately they also get less common. So, for example, stuff that's like a meter wide hits the Earth around once per day, and that's not that big a deal. I mean, you can make a big explosion in the sky and it's the kind of stuff that you hear about, you know, like the churbulence explosion in Russia recently. It's an order magnitude of a meter size thing. Often this just happens, you know, over the ocean. Nobody notices, but occasionally you get a bigger one. And if you had something like ten or twenty meters wide, this happens like every ten or fifty years, then you're starting to get energies comparable to an atomic bomb explosion.

00:24:00
Speaker 1: WHOA, I feel like we should hear about that more often. But I guess I guess you said that it happens over the ocean a lot, and so we wouldn't hear about it.

00:24:07
Speaker 2: Yeah. I had exactly the same reaction. I was like, hold on, a second, nuclear bomb explosions not that common. You think you'd hear about it. This is beyond the news. You'd feel it or something. But these things tend to happen in the upper atmosphere and often over the ocean, so they're just not observed or reported.

00:24:23
Speaker 1: But with how much like surveillance equipment we have in space, I would expect you'd see it. But I guess that surveillance equipment, you know, has only been up there since like the sixties or something like that, so we don't have that many years of data. Wow, Okay, that's the numbers you're giving are much more regular than I would have guessed. Let's move on.

00:24:44
Speaker 2: Yeah, and it's also energy deposited in the upper atmosphere, so it's not like the equivalent of somebody sitting off a nuclear weapon on land or even dropping one in the ocean. And so while the military is definitely tracking these things, and we talked about like the network of satellites that the military has when we're talking recently about interstellar asteroids and whether they've hit the Earth and whether Avilobe has actually gathered any spherials from them. So we know the folks are tracking them, it's just not that big a deal. It's like getting your shields zapped with lasers, but you know your shields are pretty strong.

00:25:14
Speaker 1: Okay, all right, So these explosions are happening in the atmosphere. So have we talked about a size yet that could reach the Earth, and is there a relationship between size and whether Yeah, there's got to be a relationship between size and whether or not it makes it to the Earth to impact, right.

00:25:30
Speaker 2: Yeah, So anything above like twenty five or fifty meters will probably make it to the surface. Anything smaller than that is probably going to burn up in the atmosphere. And once you get up to that size, we're talking about a significant amount of energy. So like one hundred meters size asteroid if it hits, which is something that happens every few thousand years, we think has as much energy as three thousand atomic bombs.

00:25:55
Speaker 1: Oh my gosh, Okay, so five thousand years. How long have we had recorded history? Do we have? And I know it could have happened in the ocean and we missed it or something, But do we have any recorded histories of this sort of thing happening?

00:26:09
Speaker 2: We do, we think, and we're going to dig into that in just a minute.

00:26:12
Speaker 1: Who suspenseful?

00:26:15
Speaker 2: And then as the things get larger, like a kilometer wide, we're talking about something every half million years. We think probably five kilometer wide asteroids happen every twenty to forty million years, and basically anything above five or ten kilometers is extinction level event. We're talking about creating creators that are like one hundred kilometers wide, tossing up enormous amounts of stuff into the atmosphere, obliterating a consonant instantly with fireballs, so like an enormous amount of energy, but fortunately very very rare.

00:26:47
Speaker 1: I don't know what to say other than maybe I'm not going to be sleeping tonight. Maybe I take it back.

00:26:53
Speaker 2: And so, of course we're really curious about if this is going to happen in the future, and when we can also look around the Earth for signs at this this happened because it's hit the Moon, it's hit basically every surface in the Solar System. The Earth is not special. The Earth also gets hit with this stuff, but only the larger ones make it down to the surface and cause impact craters.

00:27:13
Speaker 1: So now I'm realizing that I would love to know how we figured out these frequency data that you said. You know, how do we know that you get a five meter size one almost every five years? And how can we search the Earth for evidence of how often it got hit? Are you saying that we don't bother searching the Earth because it's easier to just look at the Moon.

00:27:34
Speaker 2: These are extrapolations from our stimulations of like what's out there in the Solar system, how often do we expect stuff to hit the Earth. We can also verify those and a lot of those stimulations are built on studies of impact craters on the Moon and other objects, the Moon just being super close by and like riddled with impact craters, and they do all sorts of cool studies to see like the age of craters on the Moon, by seeing how they're layered, Like if you have a fresh then it's gonna have no other craters inside of it, whereas an old crater is gonna have lots of other small craters within it. And so you can tell the age of these craters on the Moon by like how many other craters have been layered on top of them. It's super cool.

00:28:13
Speaker 1: That is super cool. And if we couldn't do that on Earth because that stuff gets covered up too fast, is that right?

00:28:19
Speaker 2: No, we do actually have evidence of craters here on Earth, though it is more complicated because we have weather and we have an atmosphere, and so only the bigger stuff leaves evidence. But there's lots of cool ways that people have figured out that formations on Earth are due to impact, Like there's certain kinds of rock that are only formed when you get a super high energy impact, Like shocked quartz. This is a structure of quartz that's only formed under extremely high pressure. Like you squeeze quartz hard enough and it changes its crystal structure and it stays that way even after you remove the pressure.

00:28:56
Speaker 1: I like that name shocked quartz. It was like, Oh, that's a surprising explosion.

00:29:02
Speaker 2: It sucks. We only actually discovered it recently in nuclear testing craters, Like when we started creating these conditions, these nuclear bombs, we discovered this shock courts. Then we found it in other places on Earth. We're like, oh, wow, this must have been a big explosion too, thousands of years ago. So it's kind of cool how modern technology has enabled us to discover the secrets of the past.

00:29:26
Speaker 1: So many positives to nuclear bomb testing.

00:29:32
Speaker 2: But earlier you were asking whether we have evidence for like these sort of smaller collisions in the recent past, And maybe my favorite one is in Estonia. This evidence in Estonia of an impact that left a crater that's like one hundred meters wide, and they think it happened in fifteen hundred BC, So this is just a few thousand years ago, you know, as we were saying, like, we expect one hundred meter wide impactors every few thousand years. So do we have any written history of this? And this is a great candidate.

00:30:01
Speaker 1: Go on, So is it the ancient Egyptians? They did a lot of writing.

00:30:07
Speaker 2: The ancient Egyptians did a lot of writing. But these are lakes in Estonia that they're pretty certain were caused by an impact. They're like these big circular lakes, and they suspect that they may actually appear in Estonian and Finnish mythology. So now this is very tenuous, of course, but you know, you're wondering, like ancient peoples when they saw this thing, what did they think? How they describe it? How would it appear in their records? Because they're not all doing astronomy. I mean, the ancient Chinese have like astronomical records way way back then, but we don't have astronomical records from everybody. You, of course, are familiar with the famous work of literature of Beowulf.

00:30:43
Speaker 1: I am indeed yeh, because you're the best adaptation ever has been written by my husband for children, because who didn't want the Beowolf for children version?

00:30:53
Speaker 2: Yes, well exactly, And so spoiler alert, Beowulf dies in the end, and he dies the hands of a fiery dragon. And in the text they call it the sky Plague, a long creature that flew at night over the coast of Greystone Cliffs, and in the poem it uses its fiery, poisonous breath to scorch and depopulate the countryside. And some people think I read a sociology paper that says that the description of the dragon and the devastation it causes has a lot in common with this impact site in Collie, And there are indeed Greystone Cliffs dearby, and so it could be that, like some fiery impact left its traces in the local mythology and ended up in the text of Beowulf.

00:31:35
Speaker 1: WHOA, that's pretty cool.

00:31:38
Speaker 2: And you know this is not scientific, of course, it's always very easy to come up with a connection where there isn't one. But it's fun to imagine how these people might have thought about these huge, devastating impact And it's something you can go and visit today. It's called Kali. I'm sure, I'm pronouncing it incorrectly kaa l I. And it's a site in Estonia with obvious impact craters.

00:32:00
Speaker 1: It's a wonderful work of fiction, particularly if you're reading the version written by my husband called be Wolf.

00:32:07
Speaker 2: Exactly, and it may have inspired some of the great literature of our civilization. But you don't actually have to travel to Estonia to see impact creators. We have an awesome one right here in.

00:32:17
Speaker 1: The US, and after a break, we'll tell you where you can find it. All right, So, for your listeners who reside in the United States, if we want to visit our nation's crater, where would we go?

00:32:42
Speaker 2: So in Arizona, there's a place well named. It's called Meteor Crater, and it's the side of an impact from forty seven thousand BC, so this is like almost fifty thousand years ago. But it's not a small site. This crater is more than a kilometer across, and it's just it's like out there in the desert. It's just like huge vast plains and then all of a sudden, enormous impact crater. You can see this thing one flying over Arizona. It's like very obvious.

00:33:10
Speaker 1: This one. I happened to know is nickel iron if it had been ice but it was the same size and going the same speed, would it matter or is it about size and speed and mass?

00:33:22
Speaker 2: Yeah, great question, It wouldn't matter so much. Like you get a similar impact crater, but this one actually left a meteor right because it's made of nickel an iron. A lot of it survived, like half of it was vaporized when it came through the atmosphere and smashed into the earth, but huge chunks of it are still lying around. They have found chunks of this asteroid before it came a meteor and now the chunks of it are called meteorite, so we can actually study it.

00:33:47
Speaker 1: Whoa dude like, is this something you can buy online? Is there that much of it?

00:33:51
Speaker 2: There's not that much of it. It's very scientifically valuable. But it also played an important role in understanding how to date geological events. Like one way we figure out how old things are, how old a rock is when it went from lava to some sort of like crystal, is by looking at the uranium inside of it. We can use uranium dating to figure out when a rock was made.

00:34:15
Speaker 1: And did this have uranium in it or does stuff in space have different amounts of uranium.

00:34:20
Speaker 2: This stuff has uranium and it so we can use this technique to figure out like when the original chunk of stuff was made before it hit the earth. But it actually also has a really cool story connected to gasoline because when they were trying to figure this stuff out, they need to understand where all the lead was in the atmosphere. The way this dating system works is that when these little crystals form inside the rock, these Zerokon crystals, they allow uranium in, but they strongly reject lead. Like the chemistry of it says lead is not allowed inside these crystals, but uranium decays into lead, and so after millions or billions of years, the uranium has transformed itself into lead. So the more the lead you find inside these crystals, the older the rock is. It's like a little clock turning uranium into lead. And you know there's no lead to start with because the crystal's repel it. So if you can measure the amounts of lead and then mounted uranium, then you can tell how old stuff is. So the chemist who was figuring this stuff out, he was trying to calibrate this and he was discovering, Oh my gosh, this lead everywhere. Like every time he tried to get a lead free environment just to like calibrate his measurements and do some tests, he was totally unable to. He had to actually go to Arizona and study a piece of this meteorite to try to get like an unspoiled piece of rock that didn't have like lead everywhere in it. And that, of course was because we had lead in our gasoline and we were pumping a huge amount of lead into our atmosphere and into our children's mouths. There's lead everywhere in the seventies, and he actually led the charge to get lead out of gasoline, not just because it was making everybody dumber, but also because he didn't like having a lead polluted atmosphere. It made it harder for him to make these measurements. And he's one of the first people to measure the age of the.

00:36:01
Speaker 1: Earth accurately better living through science.

00:36:03
Speaker 2: Yeah, and this meteorite helps us all have a safer environment for our children and understand uranium dating.

00:36:09
Speaker 1: Wow. Well, okay, so that's that's a positive thing for once. Maybe my children can listen to that chunk. But I'll just take out the lead is everywhere a part.

00:36:19
Speaker 2: Well, lead is no longer everywhere, thankfully.

00:36:22
Speaker 1: All right, So let's go even further back in time. Presumably we'll talk about an even big asteroid. Where are we going to find this one?

00:36:30
Speaker 2: So for the next biggest one, we got to go to Kazakhstan. There's a site in zamashin Kazakhstan where an impact left a crater fourteen kilometers wide about a million years ago.

00:36:44
Speaker 1: Oh okay, so how many hiroshimas would that produce? That's gotta be a lot.

00:36:50
Speaker 2: That was a really big impact. Absolutely. They think that this is essentially the most recent impact that would have produced a huge nuclear winter. Not large enough to cause a mass extinction, but large enough to really have a serious impact on the Earth's climate for many years. So this was a really large event. I mean, fourteen kilometer wide crater is like nothing to joke about.

00:37:13
Speaker 1: I'm a little surprised you can have a nuclear winter without a mass extinction, but uh, I guess nature's kind of resilience.

00:37:22
Speaker 2: By then, the mammals were already in charge, and we'd already survived from one big nuclear winter. So you know, grow out that fur coat and hunker down for a few years we.

00:37:31
Speaker 1: Got this figured out. Now can I buy any of this online?

00:37:36
Speaker 2: Actually you can. This one is so big that it left fragments everywhere, and people just go like and pick up the stuff and sell it online. And some of it is really spectacular, Like you can buy this stuff called glass foam, which shows you that the original impactor was kind of fluffy. It had these like big chunks of silicon with huge air bubbles in it. We still don't really understand exactly how it was full. And in some of these chunks of glass foam you can see the melt, like there's unspoiled chunks of glass foam. Then the other side of the rock is like melted glass foam as it passed through the atmosphere and the plasma from the friction actually melted the edge of this thing. It's really pretty spectacular. So yeah, you can just go online and buy Zamanschite.

00:38:20
Speaker 1: Quite the conversation piece, And you know, there's a lot of studio science surrounding this stuff.

00:38:25
Speaker 2: People think it's mystical. I look for some of this stuff for sale, and it was advertised as having the capacity to quote blast away bad forces and negative people who block your life's path. So I'm not sure that sounds great big if true, right right, Yeah, so we'll see. I'm not going to endorse those claims, but it is pretty cool to own a chunk of stuff that came from space that like floated around the Solar System for a while and then decided to end its days here on Earth.

00:39:00
Speaker 1: That is pretty cool, all right. And so now we're going to another stan. We're heading to Jikastan. Tell us about this one.

00:39:09
Speaker 2: Yeah, So Karakul to Jikastan is the site of a disputed impact. It's basically a huge leak. And when people first went to space and saw pictures of him from space, they were like, hold on a second, look at the shape of that thing. That looks like an impact crater.

00:39:24
Speaker 1: And that's because it's very circular.

00:39:26
Speaker 2: It's mostly circular. It's actually got like a big peninsula in the middle. Some people think is also part of the evidence, because when a rock hits the Earth, it can have all sorts of weird seismic bounce backs, So some people think it's consistent with a crater. Some people are like, nah, you're just imagining it. It's like staring at clouds. But If it is an impact crater, it's an enormous one. This thing is fifty kilometers wide, and they think it probably happened somewhere between five and twenty million years ago. So this would have been big news a long time ago.

00:40:00
Speaker 1: So why do we have to dispute this? Why can't we know for sure? Why can't we look for like shocked quartz or tech tight or something.

00:40:06
Speaker 2: Yeah, people have done that, but you know, these things aren't easy to find when it's so old. Even the big crater like the one we'll talk about next that killed the dinosaur, it took a long time before people were able to like find the evidence for it. So this one was discovered fairly recently, and people are still studying and still trying to find those pieces of evidence that might be out there.

00:40:23
Speaker 1: All right, all right, so then let's move on to the dinosaur killer.

00:40:27
Speaker 2: So probably the most famous impact site on Earth is Do you know how to pronounce this one? Kelly? No, do you want to try on air?

00:40:36
Speaker 4: Uh?

00:40:37
Speaker 1: Chick kloop?

00:40:38
Speaker 2: All right, We're gonna go with that.

00:40:39
Speaker 1: I think I had a Russian in there. I'm not sure that belongs.

00:40:43
Speaker 2: Sorry, this is the one in the Yucatan. You know how Mexico basically has that little swoop in it, and they think that that's the edge of an impact crater, the one that probably took out the dinosaurs sixty five million years ago. And this one's enormous, right, it's one hundred and fifty kilometers wide, and they think that an impactor like ten kilometers wide hit the Earth and left that impact crater. One we can see now from space. It's pretty amazing.

00:41:10
Speaker 1: But we do have shocked quarts and tech tights from this one.

00:41:13
Speaker 2: From this one, we actually do have very specific evidence. You can see in the ring around the edge, shock quarts everywhere, and they have tech tights, which are these little bits of glass that are created during the impact and then thrown everywhere that are different from volcanic glass and also like don't have the geology of the local environment, so they seem very obviously like created from some impactor. So here we have very strong evidence that there really was an impact sixty five million years ago. People still argue about whether it's the reason the dinosaurs went extinct, et cetera, et cetera, et cetera, but we're pretty confident that it happened, and it would lead to crazy things like tsunamis a kilometer high clouds of dust and ash and steam, including like twenty five trillion tons of material, some of which escaped the Earth and is still floating around in the Solar system, like explosive dust from this impact is still out there.

00:42:08
Speaker 1: It's crazy, right, that's intense.

00:42:10
Speaker 2: Yeah, So this is the most famous impact crater on Earth when people know about the most, but it's actually probably not the biggest, the most dramatic impact in Earth's history.

00:42:19
Speaker 1: No, this is the biggest one that I know about, and I feel pretty good because I think for the listeners, this was the one that most of them talked about as well. So which one is bigger?

00:42:31
Speaker 2: So there's an impact crater in South Africa. It's called Redifort. I'm sure I'm mispronouncing it. And this one is three hundred kilometers wide, so it's twice as wide as the one that killed the dinosaurs, Oh my gosh. But this one is also much much older. They date this one to like two billion years ago, so when life was very very primitive, and because it's so old, it's been eroded significantly, like mostly it looks like like a partial ring of hills and there's a dome in the middle of it. You have to sort of like squinch your eyes a little bit to even see it.

00:43:07
Speaker 1: Why is there a dome? Why are rolling hills the sign of an impact crater. I would think that like Ohio being flat would be the sign of an impact crater, But I don't associate hills with impact craters.

00:43:20
Speaker 2: Yeah, so the dome is really fascinating. When a really big impact or hits the Earth, you don't just get a crater for a huge one, you actually get to bounce back in the center. The Earth is like a big waterbed. Right you hit it, it's gonna bounce back a little bit. And so if it's big enough, you get this bounce back, this dome in the center. And then you also don't just get like one circle. You can have multiple rings. It's like the seismic waves travel through the Earth and they get frozen in several places. It's not actually something that's understood very well. You can see it in a few other places around the Solar System, impact craters with multiple rings around them, but geologists are still trying to understandactly how that happens. But if you look at these sets of hills in South Africa, you can see that there are multiple rings surrounding this dome. So that looks a lot like a huge impact.

00:44:10
Speaker 1: The bounce back that you're talking about. That that's the like you said, the lake in Tajikastan has like an island in the middle. That's the that's the bounce back that you were talking about. Okay, got it, Yeah exactly.

00:44:22
Speaker 2: But because it's so old, it's not really complete anymore. Like if you've seen this thing when it was fresh, you probably would see like a big dome in the middle and then complete rings around it, multiple complete rings. But because it's been two billion years since the incident, a lot of those have just eroded away. So now you have incomplete rings of hills, so partial rings of hills around the dome.

00:44:44
Speaker 1: But the good news is that all of this has happened in the past half the day. Listeners, it's been nice having you here.

00:44:52
Speaker 2: Sleep well, and then you know, as the listeners mentioned, maybe the most dramatic incident in Earth history was the formation of the moon. Right, we think that the Earth was hit by a proto planet billions and billions of years ago, which essentially obliterated the entire planet, turned the entire surface into lava, which spun out and turned into the Earth and the Moon. So this is probably the most dramatic event in Earth's history, so dramatic that it doesn't even leave an impact crater, right, It just like vaporizes the whole planet. But they actually think that they found in the Earth's core some evidence of this impact.

00:45:29
Speaker 1: And what is the evidence.

00:45:30
Speaker 2: They look inside the Earth, you know, to like the lower most mantle, and they find that some chunks of the mantle look a little bit different. It's like a different composition, different density, and they think that what they're seeing there is mantle from the impact or from FEA that made its way down to proto Earth's lower mantle. So basically, like the inner core of our planet is partially from the inner core of this huge impactor.

00:45:54
Speaker 1: That's incredible.

00:45:55
Speaker 2: Yeah, So the blobs, the density patterns inside the Earth show this tell tail sign of this crazy cataclysmic impact, even more dramatic than the one that killed the dinosaurs, even more dramatic than this one that left these eroded rings in South Africa.

00:46:10
Speaker 1: Glad I wasn't there, and I sure do like the mood.

00:46:15
Speaker 2: And as much as these all seem scary, Kelly, these all were crucial in life turning out the way that it did. Right. If things had happened differently, we wouldn't be here. And so we can say thank you to the solar system for raining death down on other people's ancestors for so many years.

00:46:31
Speaker 1: Yes, thank you for this past, but never again in the future. Right, there's no risk of this happening, say, I don't know in the next decade or so.

00:46:41
Speaker 2: There's actually an asteroid that's a few hundred meters across that's likely to make a close pass in April of twenty twenty nine. It's called Apofis, and they predict that it's going to come by Friday the thirteenth in April twenty twenty nine. But it's just supposed to make a clut us.

00:46:59
Speaker 4: But it's not.

00:47:00
Speaker 1: It's not coming on Friday the thirteenth, Are you kidding?

00:47:02
Speaker 2: I am not making that part of that part is real. You gotta wonder what it's like to be that scientist, like predicting the day it's going to be the closest approach and having to be like Friday the thirteenth.

00:47:16
Speaker 1: Or I wonder if you have like a Cassandra syndrome sort of thing, like, no one's gonna believe me if I say it's coming on Friday the thirteen.

00:47:23
Speaker 2: That's right.

00:47:24
Speaker 1: How close is close when you say it's going to make a close pass?

00:47:27
Speaker 2: You know, astronomically speaking, anything that comes like with between the Earth and the Moon is pretty close. But that doesn't mean it's very dangerous. The Earth is still a very small target compared to the vastness of space, and it's hard to predict these things years out. So as time gets closer, they'll predict it more accurately, and very likely we'll all be fine.

00:47:46
Speaker 1: But it's like within the range of error right now that Earth could get hit.

00:47:51
Speaker 2: Depends how generous you want to be with range of error. There's always systematic uncertainties that haven't accounted for that increase the envelope to include the Earth. So yeah, it's possible it could hit the Earth. Maybe we should be thinking about Plan B Kelly, what do you think?

00:48:04
Speaker 1: I don't know, mostly because I think there's zero chance that we could have a self sustaining settlement on Mars by twenty twenty nine. So if Earth is going to be destroyed in twenty twenty nine. You know, a Mars settlement would just be like a couple years behind. Maybe you'd buy us a couple more years or something, but I doubt it. For more information, check out A City on Mars by Kelly and Zach Widersmith.

00:48:30
Speaker 2: I mean, if Earth's civilization is going to be destroyed in five years anyway, might as well spend all your money on books right now.

00:48:35
Speaker 1: That's exactly well, it's a good deal, even if there's not a world ending cataclysm coming.

00:48:42
Speaker 2: Well, it's fun to think about the crazy history of the Earth. You know. It hasn't just been bubbling oceans and hot tubs and all sorts of cozy times. It's been dramatic and cataclysmic. And we can find the evidence of those impacts on the surface of other objects in the Solar System, but also year on Earth. And I love when geologists unearth the evidence here on Earth for crazy events in our deep history.

00:49:07
Speaker 1: Way to go, geologists, don't let it happen again.

00:49:13
Speaker 2: It's on you, exactly. We're counting on you, well, all right, even if we do nothing about it's knowing how this works and knowing the history of the impacts. Maybe you will help us figure out how to prevent them in the future. Thanks very much everybody for listening, and thanks Kelly for joining us today.

00:49:30
Speaker 1: Thanks for having me on the show. It was quote unquote fun as always.

00:49:37
Speaker 2: All Right, everyone, tune in next time 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 podcast from iHeartRadio, visit the iHeartRadio Apple Apple Podcasts, or wherever you listen to your favorite shows.