Listener Questions #41

This is an iHeart podcast. Guaranteed human. The world is a little bit... 18 month contract. Prices may vary. Verify at gigaklear.com Kelly, tell me all about Earthworms, but rain it in a bit. Don't make me squirm. Long before dark energy blew us all away, was there already a galaxy called the Milky Way? Kelly, pray tell. How does the snail make its shell? And let me know if it grows like a toenail as well. We're good at this. Whatever questions keep you up at night, Daniel and Kelly's answers will make it alright. Welcome to Listener Questions Episode Number 41. Hi, I'm Daniel. I study physics and aliens, and we are one number away from my favorite number. Hello, I'm Kelly Weedersmith. I study parasites and space. And is that because you, predictably as part of the community of physicists, have to like Douglas Adams' Hitchhiker's Guide to the Galaxy and your favorite number is 42? No, I don't have to like Douglas Adams. I sincerely like Douglas Adams because it's great stuff and it's totally hilarious. Fair enough. When we first started writing Soonish and we started engaging with space people, there were so many references to that book. I was like, if I want these interviews to go well, I have to become way more familiar with Douglas Adams' work. And so I had to, I read a bunch of stuff so that I could get the references and keep up with folks. Oh no, were you ignorant of the canon before that? I was. I was a different kind of nerd, but now I'm the right kind of nerd. Our kind of nerd. No, we love all kinds of nerds on this show. As long as you're curious about the universe and want to understand how things work, we embrace your inner nerd. We embrace your outer nerd. We embrace every part of your nerddom. Well, that sounded weird actually. I mean, that doesn't sound any weirder than most of the things we say, but way to go nerds. And today my nerdy topics both involve invertebrates. Hmm. Innertebrates. That sounds great. Innertebrates? What did you say? I said innertebrates. Oh, I love it. I love it. Yes, exactly. We have coined a new non-Latin name for these squiggly creatures. Well, we love hearing from you. We love knowing what is squiggling through your brain, making you curious about the universe and bringing out your inner or outer or whatever nerd. So, nerd out and write to us. Send us your questions and your curiosity to questions at Daniel and Kelly.org. We say we respond to every email we really, really do. We'll write right back to you. You may be surprised, but you will have an answer. That's right. And the first person to nerd out with us this week is Tan. Yo, Daniel and Kelly just caught your earthworm segment on the AMA and now I have a million questions. Where do earthworms actually come from? Are they just everywhere? How do they reproduce? Do they have enemies? Are they always a net positive or is it more complicated than that? And honestly, should I feel bad stepping on them or accidentally slicing one while digging? I could Google this, but I genuinely want to hear it straight from the horse's mouth. You two make this so much more interesting than a such result ever could. Can't wait to hear it. See ya. Well, I've never been called a horse's mouth, but I am okay with that. That's not the worst thing I've been called. Well, I've never been called a horse either, though I have the nose to rival one. But I was confused about this question from the very beginning. Did we already do a segment on earthworms? Is that what inspired this question? No, I assumed that that was a mistyping and that there was a segment on something else that got them excited and got them thinking about earthworms. Because we've done so many questions and so many episodes that sometimes I don't even remember and somebody will write in and say, hey, will you do an episode about this? And I think, oh, great idea. And then I discover, oh, I already have an outline for that. Oh, because we did that last year. Sometimes when you're so, you know, you and I record like a month and a half before an episode goes live. And sometimes when our amazing audio guy sends us a draft, I'll be like, this is totally new to me. I don't remember any of this. And that's great. You get to listen with fresh ears. All right, so let's assume we have memories longer than an earthworm. Tell us what is the answer to Tann's question about earthworms? What are earthworms and where do they come from? Yeah, so there's there's lots of questions in this question. So earthworms, they're in phylum, Annalida, which means that there I know, I know Daniel's laughing is like, oh my gosh, she started there. That's definitely an answer. That's definitely information that really helps everybody. Annalida means little rings. And so we're starting by describing how they look. So they've got their segmented into lots of little rings that are related to leeches. Okay, there you go. And are they everywhere was one of the first questions. And the answer is no, they're not everywhere. Actually, they're fewer places than I might have imagined. So in North America, for example, we had a glacial period where glaciers came down, you know, really far like up to the Great Lakes and a little past in some regions. And you don't have earthworms there anymore because they couldn't survive that. Or you do have earthworms there now, but they're not native. Wow. Glaciers kill earthworms? Yeah. So earthworms can be over 75% water by weight. And so when it gets really, really cold, they freeze and die. And you also don't find a lot of them in deserts because if you're more than 75% water by weight, the desert's not a great place for you to be. But when you freeze an earthworm, it can't come back from that. I know that some critters, if they're simple enough, you can freeze them and thaw them and then they're just like happy again. Yeah. You know, maybe there's some earthworms out there that can survive freezing and thawing, but I think usually the strategy is to bury underneath leaf litter so that you don't freeze or bury underground so that you don't freeze. But it is the case that in places that are far north, there are not native earthworms. And we think that that's because the last glaciation event wiped them out. Wow. So earthworms are more fragile than I expected. Basically, you need to have liquid water and you need to never totally dry up or they all die or totally freeze or they all die. Does that mean that you can only have earthworms at a place if all through recorded history it's never frozen or been totally arid? No, because humans move stuff around all the time. So for example, like Minnesota, I looked at their Department of Natural Resources website. They said that they don't really have native earthworms, but they still have loads of earthworms. And the reason is because they have European earthworms, which we literally think were brought here by some of the earliest settlers like Jamestown, they probably brought earthworms with them. You mean like they were packing for their trip and they were like, don't forget the earthworms or like they brought their compost because it's such good soil or earthworms were along for the ride somehow in a sly way. Could have been a couple of those things. But you know, for example, if they wanted to bring with them, I don't know, an apple tree, it probably would have been potted. And in that pot, there probably would have been earthworms or earthworm eggs. And so, you know, whenever you go to like a garden center and you pick up a pot, if that plant came from somewhere far away, you're probably getting foreign earthworms with it. And so we move them around a lot. So you find them just about everywhere. I think if we were going to pack up our house and move, Katrina would want to bring her worms because she has like a dedicated compost pile and she's always nurturing those worms. And so I think she has a deep affinity for her worms. Yeah. Well, and you know, I think there's no getting rid of the earthworms that are like in our compost piles or in our gardens where they are doing some helpful things like they're here. You can probably think of them as naturalized, which is to say they are not going anywhere. But there's an earthworm that is slightly newer that's causing problems. It's from Asia and it's like bigger and it can jump. And so I think sometimes they get called jumping worms and they kind of freak people out. But these are actually becoming a bit of a problem. Wait, they can jump? Until this moment, I had only like positive fuzzy gooey thoughts about earthworms, even though they look just like tapeworms. Because they like stay in the ground and don't really bother you. I was like, I'm cool with earthworms. Now, if you're telling me they're like jumping out of the ground onto people, I'm getting a little freaked out. Well, that's only the first way I'm going to blow your mind today, Daniel, because most people only think good things about earthworms, as you've said. So stick with me here. We're going to get back to the jumping worms and I'm going to tell you that they're not all good all the time. Wow, you're going to demolish the earthworms millions of years of work to build good PR, huh? They do have good PR, but you know, it's going down. It's going down. All right. Big earthworms are going to come for you, Kelly. Be careful. Ooh, ooh, they could do me in with slime. That was a bad way to go. So there's three kinds of earthworms and I guess I kind of thought about worms as like they're all doing kind of the same thing. But there's worms that live in the leaf litter, so they're not really burrowing underground. They're just eating like dead plant stuff. There's worms that live in what's called the mineral soil. So it's just like the top layer of soil and they're like eating organic stuff and feeding on soil and dead leaves and stuff. And then there's deep soil burrowers. They, so instead of burrowing sort of parallel to the surface, so like going along underneath the surface, but traveling kind of near the surface. These go way deep down and they will pick leaves from the upper leaf litter and pull them down with them into their burrowing. And so by doing this, they get nutrients from the surface deeper into the soil and all of this burrowing that gets done by the mineral soil dwellers and the deep soil burrowers, say that five times fast, helps to aerate the soil. So in a lot of cases, earthworms can be good. So why do these earthworms take their snack all the way down into a deep burrow before eating it? I'm going to guess that this was an adaptation to avoid certain kinds of predators. You know, I think some birds can like dig through the top layer of soil to try to find the earthworms. But if you're really deep down there at some point, the birds don't have long enough beaks. And so this was probably like a nice little refuge to get away. I see that way they can like hang out in the refuge, enjoy their snack, not worry about those crows. But a fun fact I learned is that Darwin sort of towards the end of his life became really interested in earthworms. And he was trying to figure out are earthworms smart in any way. And so, you know, he determined they really couldn't hear. He had people like play music for them. He put them on a piano. They didn't respond. But he did think it was interesting that the deep soil burrowers, when they went to go pull a leaf into their burrow, would grab the side of the leaf that's like kind of pointy and try to pull it in that way, which would make more sense than trying to pull it in from the side, because it would be harder to get it down into your hole. And so he interpreted that as earthworms being sort of smart, that they know like what's the best site to pull on something to get it into your burrow. This was all new to me. Well, I interpret them as smart for going down into their burrow to enjoy their snack. You know, the same way that like I judge people who eat out of the fridge instead of like making a plate of food and going to sit at the table before eating it. Uh-oh. Wait, you're judging people? Why do you have to be so judgy? Why can't you just be like, I don't do it that way? But it's fine that you do it that way. It's not fine that people eat out of the fridge. Do you also like drink out of the orange juice container and then just put it back in the fridge? I'm moving on. No, I don't. I don't do that. But only because it's too full and it would be unwieldy and it would spill all over my face. But if they came in smaller containers, I might. Okay. So then there was another question about how do they reproduce? And I guess not knowing any biology since ninth grade is that they just like split in half or is it asexual reproduction? They're just like one big earthworm becomes two little earthworms? Oh, I love that. No, not even close, but like, but I, that's an interesting way to think about it. Uh, I didn't. Wow, there's people out there that think that. There's me, for example. There's Daniel. So then Kelly, tell me how do earthworms make more earthworms? Okay. So they're hermaphrodites. They find another earthworm and they start slithering up next to each other. And while their bodies are touching, they release sperm and eggs. And then they have, you know how like if you look at an earthworm, they've got like a ring, almost like they call it a saddle or it's called a clatellum. But anyway, so that ring starts secreting loads of slimy, slimy, slimy mucus. And then they shimmy the mucus off of it. And as the mucus tube moves along the body of the earthworm, it picks up the sperm from the other individual and the eggs that they had deposited and puts it in that mucus ball so they can all mix together and get fertilized. And then it leaves those in the soil so that they can then hatch. So the mucus ball has sperm from both worms and eggs from both worms. You know, I guess I can't imagine how it could have it from only one of them, giving that the picture that I'm looking at, they're really... They're really touching pretty close. So there's probably some mixing there. But I think the point was to grab the eggs from the worm that made the slime and mix it with the sperm that was just released from the individual who's cuddling up to that worm. And mix them that way. And then now you've got a slime ball to keep your eggs from desiccating, from drying out, and you leave it behind in some moist soil. Wow, that is a lot slimmer than I had in mind. No, I like the idea that they just split and then there's two of them. That's great. But can't you take an earthworm and cut it in half and you get two earthworms? I think that that doesn't work as well as most people imagine it does. And it kind of depends on where the cut happens. But can you get two earthworms? I think you can get the survival of the earthworm that you cut. It will regenerate its tail, but I don't think that two earthworms slither away if you cut one in half. Let's look that up really quick. I can't believe I'm typing this as a necologist. Can you cut an earthworm in half and get two live earthworms? I'm pretty sure the answer is no. AI says no. Cutting an earthworm in half does not create two live worms. You'll typically end up with one dead worm. You mean nobody's achieved it yet, so there's an open question in biology out there. Wow. There's a challenge to all you aspiring experimental biologists. I think the answer is just no, everybody. Don't spend too much time on this. Don't go out there with scissors and cut all your earthworms in half. Yeah, no, that'd be mean. Some of them might survive depending on where you cut them, but it would still be mean. All right. And so tell us who else is mean to earthworms and eats them. Who are the natural predators of earthworms other than experimental biologists? We don't know if we count as predators. We're not eating them, hopefully. But I mean loads of things eat earthworms. Birds eat earthworms. There are snakes that eat earthworms. They're an easy snack. I'm betting that raccoons and opossums eat earthworms when they find them. I think Mrs. Twit ate earthworms in that novel. What novel is that? Is the novel called Mrs. Twit? No, it's the Twits by Roald Dahl. The two grumpy people who would play terrible practical jokes on each other because they have a terrible marriage. Oh, that's no good. I don't aspire to that. That's a children's story. Roald Dahl's children's stories are all a little dark. I remember that. James the Giant Peach, pretty dark. Yeah, well the parents usually die in the beginning of most of his stories. As a father reading this to your kid, you're like, this is an interesting way to go. Anyway, back to the earthworms. So you said birds and snakes. Birds and snakes and possums and raccoons. But I think perhaps the question I'm most looking forward to digging into is one of the last ones, which is are they just generally or always net positive? Big earthworm is listening. Be careful. Hey, big earthworm, I'm coming for you because the answer is no. Some of them are bad. So for example, if you're living in Canada, an area where the glaciers killed off any possible native earthworms in the past, those forests are still doing fine. And in fact, they're accumulating leaf litter because one of the things that the earthworms do is break down leaf litter. But so they've been accumulating leaf litter. And now in that leaf litter, you get things like salamanders and insects. And you've got a whole community of things that are living in that leaf litter. And so now we're getting those jumping worms that are not only unsightly and jumpy and very disconcerting, but they also break down the leaf litter very quickly. And so you have an area where you used to have a really nice habitat. Suddenly these earthworms come in and now the leaf litter is like broken down and gone. And a bunch of native species have lost their habitat. And so usually like if you go in a garden, the earthworms that you have in the garden, they're probably helping your plants. They're probably good. But when they get into like more natural systems, they're not good. And now you usually don't find native earthworms unless you're like in the middle of the woods away from human disturbances and non-native species. That's where you got to go to find the native ones. I understand the argument that breaking down the leaf litter is bad for some kind of critters that like leaf litter. But is that the same as arguing that it's bad overall? There's going to be some critters that benefit from having less leaf litter. And like also isn't it good for a forest to not have leaf litter around in case of a forest fire? So these forests were fine for like thousands of years without the earthworms. And there are some forests where the plants are adapted to deal with periodic fires. And so it doesn't necessarily mean because they have leaf litter, those fires are going to kill all of the trees in the area. And so yes, when leaf litter goes away, there are some species that benefit and some species that don't. But the sort of like baseline situation for these ecosystems was an expectation that there would be some leaf litter and an expectation that sometimes there'd be fires. So not always good actually, but probably fine if they're in your garden. And so the last question is, should you feel bad about stepping on them or unintentionally slicing them, digging into the earth? Yeah. All right. So now we're going to the big moral questions of the day. I mean, my somewhat controversial opinion as an ecologist is that I do feel bad when I kill invasive species. In most cases, it's not their fault that they're here. We did something to bring them here. And so I usually try, like even when I've been doing experiments and I've had to euthanize invasive species to study something about them, like what they were eating. I've always tried to do it in the most humane way. And when I see not native earthworms on the sidewalk, I don't step on them, not just because that would be gross. And I don't really want to like see them on my sidewalks mooshed. But also like, I don't know, me stepping on one isn't going to make the problem of invasive earthworms or what are non-native earthworms any better. And so I try to avoid them, but I also, I guess I have to be honest, if I accidentally step on one and then I see it, I don't lose loads of sleep because what can I do? But I don't know, what do you think, Daniel? I think it's silly to put moral questions on a lot of these issues. You know, you are not like wielding the heel of moral justice by squishing some invasive species. I also don't think it's like bad that species die out or that ecosystems change. I think you're going to look at the bigger picture, like is there enough diversity? Are things evolving rather than worrying about any individual species too much? I think a lot of what you said, I would agree with, maybe not all of it, but we will have some interesting conversations in our rewilding episode because the question there is, you know, should you be bringing back species that have been lost from a system for a long time? And I think, you know, it depends on what kind of ecosystem services they're providing. And anyway, I think that'll be a fun sort of philosophical conversation we can have about, you know, what our role is and when we should care and when we shouldn't. I also think that the fact that 10 is even asking if you should feel bad about unintentionally slicing them tells you that 10 is a thoughtful person and shouldn't feel bad. It's unintentional. You've already felt bad, obviously. On behalf of the earthworms, we forgive you. I don't know if I speak for the earthworm as a horse's mouth. You definitely don't. You're out here bad-mouthing the earthworms, if anything. That's right. That's right. But I appreciate your question and I appreciate your concern and I look forward to hearing your response to this little mini lecture on earthworms. Hey, Daniel and Kelly, 10 here. I just finished the episode and I did not expect to walk away with my mind blown. And sorry for the confusion about the AMA reference. That was from a past episode. I don't remember which one, but that's what got me thinking about earthworms in the first place. And so Kelly, the jumping worms really got me. I was perfectly fine with earthworms my whole life and then you drop that, they can jump? Man, and now I'm questioning everything. So thanks for that. The Darwin detail stuck with me. The man already changed the biology forever and then spent the end of his life watching earthworms. You know, that's the kind of curiosity I respect. And lastly, the ecological impact. I came in thinking earthworms are universally good, but finding out that they could actually disrupt native ecosystem completely reframe things for me. So yeah, thank you both. I appreciate it. And this is exactly why I listened to you two. Take care. And we're back from a conversation that makes my stomach turn a little bit because I think earthworms are a little bit gross to a conversation that sounds kind of delicious. Our next question is about the Milky Way and it's from Alice. Alice is an old friend. She's been listening for a long time and writing to us with questions. I think she's a defense attorney in the Bronx. So thanks very much, Alice, for your question. And this question is about the Milky Way, but it is not a tasty question you're going to bite into that we are going to be talking about lots of dark things in the universe. We're not going to get into dark chocolate. OK, well, let's go ahead and hear Alice's question. Hi, Alice. Hi, Daniel and Kelly. This is Alice from the Bronx, New York. I have a question. Is it possible that space was already expanding before the Milky Way was born and that the stars and galaxies of the Milky Way formed from a nebulae? OK, thanks. Bye. So before we dig into the history of the universe, Kelly, I want your non-physicist interpretation of this question. Oh, no. What do you think Alice is asking? Well, so I would need to know what a nebula is, which if you had asked me earlier, hey, Kelly, do you know what a nebula is? I would have been like, yeah, of course. But now now I'm like, what is a nebula? Is it just I thought it was like it's like a group of galaxies or something, right? No, what is a nebula? Make sure you get that definition correct. This is great. You're like, when you cut a worm in half, do you get two? And I'm like, is a nebula a group of galaxies? We are losing our credibility. So a nebula is just a big cloud of gas, right? In the Milky Way, we have stars and we have planets and stuff. We also have vast clouds of gas that have not collapsed into stars and planets. And they're like the breeding ground for new stars sometimes. And historically, some of the things that we see in the sky, which we used to call nebula, we discovered are actually galaxies. That's like Hubble's big discovery. Some of these smudgy things are actually distant galaxies, not clouds of gas in our own galaxy. I got to say, I am so excited to start making fart jokes with my kids that involve nebulas that I can start to get them excited about like cosmology and stuff. And that is going to be my end for my 12 year old. So anyway, OK, so we know that space is expanding since the Big Bang. Was it already expanding? So I'm guessing the answer is going to be yes, because space has been expanding since the Big Bang. So it was already expanding and that the stars of the Milky Way formed from a ball of gas. What do you think this question means, Daniel? I think this question is asking about the history of the universe and the formation of galaxies and how those two things play off of each other. So I thought, let's go through the history of the universe and give the context and then we'll go through the development of galaxies, how the Milky Way was born. And then let's come back and ask you again in that context what you think Alice is asking so that we can make sure we nail her question. OK, perfect. So let's start with the history of the universe. Yes, so we don't know how the universe began. Remember, we have a theory called the Big Bang Theory, which takes us back to a very early hot dense state. But the Big Bang Theory does not suggest where that came from. It does not include a singularity, lots of misunderstanding and miscommunication about the nature of the Big Bang Theory and the scientific understanding of the early universe. But what you should have in your mind is a very hot, very dense state. And that came from, we don't know what, maybe some earlier field, the inflecton field or something, all very speculative. But what you have in that first state is a lot of matter and antimatter, which formed again, we don't know from where. OK, and then? And because there's a lot of matter and a lot of antimatter, you get a lot of annihilation. Electrons run into positrons, turn into photons. Quarks run into anti-quarks, turn into photons or gluons. And so very, very early on, most of the matter in the universe disappears and we're left with radiation. So we start with lots of matter and antimatter and then very quickly that converts to a very little bit of matter left over because it was more matter than antimatter and then mostly photons. The universe mostly filled with photons. OK, so whenever you say very, very little matter, I always think, but the earth is huge, but this is like a cosmic sense. Yeah, that's exactly right. So there's enough matter to make planets and galaxies, but relatively it's small. Relative to how much matter we had before that, it's like one billionth of the matter is left over. Oh, wow. So the amount of matter to make the earth and the galaxies and the stars and everything is one billionth of the original amount of matter that was in the universe, most of which annihilated with the equivalent amount of antimatter. Wow. OK. All right. And so at this point, is any of that matter nebula? No, it's more like a plasma. It's still very dense, right? It's still very hot. There's photons everywhere. There's still electrons and quarks. I wouldn't call this a nebula. It's just like a hot early universe plasma. And there's also dark matter there, right? When we made the original particles, we also made dark matter. So we have dark matter and we have normal matter and there's a little bit of dark energy. So we think the dark energy is just the energy in space. The universe was very, very compact. So there wasn't a whole lot. And so there's not a whole lot of dark energy as like a fraction of the energy of the universe. So we start out mostly photons, but the universe is expanding, right? And for about 50,000 years, photons still reign supreme. Most of the energy in the universe is in photons for the first 50,000 years. But the universe is expanding. And what happens when the universe expands is that the energy density goes down. And that seems like it makes sense. You know, if you have like one ping pong ball per cubic meter and you expand the volume without adding any more ping pong balls, then the density of ping pong balls goes down because you have the same number in the numerator and you've increased the denominator so the energy density drops. And that's how normal matter gets diluted when you expand the universe. You have protons, you expand the universe, now you have less density of protons. But that's not the way everything behaves when you expand the universe. And that's really crucial for understanding the whole history of the universe because radiation, when you expand the universe, it also gets diluted. You have fewer photons per cubic meter because you have the same number of photons and more cubic meters. But, crucially, those photons also lose energy. You expand the universe, it stretches the photons to a longer wavelength, which is less energy. This is one of the ways energy is not conserved in the early universe. So the energy density of photons drops more quickly than the energy density of matter. Okay. And so I'm finding myself wondering now, we've spent a lot of time on energy. Could you signpost us to why energy is going to be important for understanding the answer to the question? Yes, exactly. Because the energy fractions of the universe, how much of it is in dark energy, it controls the expansion of the universe. Okay. And the question is about the universe expansion. So at this early moment, we don't have a lot of dark energy in the universe. And so the universe is expanding, but that expansion is actually slowing down. Because there's so much matter and radiation, all this kind of energy density that creates gravity. So the expansion is slowing down. So the universe was expanding and it's mostly photons. And then after 50,000 years, it becomes matter dominated. But in all of these cases, the major energy density of the universe tends to slow down the acceleration. Okay, got it. All right. So we are still in an expanding period. What kind of timeframe are we in right now? So for the first 50,000 years, the universe is mostly photons. After that, it's mostly matter for the next nine billion years. The universe is mostly matter and the expansion is slowing down. Okay. But dark energy is growing because as the universe expands, radiation falls off in energy density very quickly. Matter falls off in energy density, but dark energy does not. When you create new space, you get new dark energy. So if you expand the universe, even if that expansion is slowing down, you're creating new chunks of space. Those come with new dark energy. So the dark energy fraction of the universe is growing. And at some point it starts to dominate and it can overcome the effects of gravity of all this matter and these photons. And that's when the expansion universe turns around and begins accelerating again around four billion years ago. And that's only because of this energy density argument. As the universe expands, the fraction of dark energy goes up because dark energy doesn't get diluted. And so now the universe is expanding and accelerating for the last few billion years because we're in a dark energy dominated period. Okay. All right. So now I'm trying to situate the Milky Way in this story. Yeah. When did the Milky Way form during the deceleration or the acceleration phase? Yeah. So the Milky Way is very, very old. Our solar system is only about four and a half billion years old, but we see much older stars in the Milky Way, which suggests that it's something like 13 billion years old, which is crazy because it means it formed in the very, very early universe. Like when the universe was less than a billion years old. And the way galaxies form is you get a little baby galaxy formed from the collapse of a bunch of clouds of gas. You might call them nebula. Okay. Into stars, right? Okay. And then you get like a little baby galaxy of all those stars. And there's another little baby galaxy nearby. Those baby galaxies swirl together and merge and you get bigger galaxies formed by combining smaller galaxies. Okay. So the Milky Way started around 13-ish billion years ago, maybe a little bit more, from metal-poor stars. There's mostly just hydrogen in the universe and then grew through mergers, occasionally like a really big merger of two like equally sized galaxies. We think around 11 billion years ago, there was a merger between two galaxies we call Gaia and Enceladus, not to be confused with the solar system moon that formed the majority of the Milky Way. And then around nine billion years ago, the structure was there. You had the disk, et cetera. And that's when a lot of stars get born because you got the compression of a lot of this gas and dust together. And so that's the sort of rough version of the Milky Way. It was born when the universe was expanding, but decelerating. All right. So for as long as we've known about, space has been expanding. Yes, it's always been expanding. Always been expanding, but at some point you were able to get nebula. And you were able to start getting nebula sometime after 50,000 years ago? Yeah. And around 380,000 years ago, protons and electrons found each other and the universe cooled enough that they settled into like neutral hydrogen, which formed big clouds of gas and seeded the first stars. Okay. And so you've got these nebula and galaxies are born when a bunch of stuff starts clumping together. Yeah, collapsing into stars. Collapsing into stars. And everything's already expanding when that's happening. And so is it possible that the Milky Way wasn't formed by a nebula? Because now I'm thinking that all the gas and junk out there, you'd count as a nebula. But is a nebula just like when you have a bunch of gas and stuff like in a small contained area? Or yeah, at what point do you get a nebula? Or is it like, there's a threshold question? Well, people think of the universe as mostly stars, but it's really mostly not. A lot of the mass of the galaxy is in huge clouds of gas and dust. Most of the universe is still hydrogen, despite the work of stars. And most of the universe is not collapsed into stars, despite the work of gravity. So we're still sort of early in the universe. We started out basically huge clouds of hydrogen. We're mostly still huge clouds of hydrogen. So nebula collapse formed stars, which made the Milky Way. And then there's still nebula within the Milky Way that have not yet collapsed into stars. And there's some galaxies out there where star collapse has basically stopped. That's called quenching. And so it's the process we don't understand super well. Another question mark is exactly how the Milky Way began. You know, these little red dot mysteries about the very early universe suggest that it's a lot we don't understand about how galaxies formed and how they got their supermassive black holes at their hearts. Lots of good questions about how that happened in the early universe. But I think the answer to Alice's question, and you tell me if you think we're answering the right one, is that when the Milky Way was born out of the collapse of a nebula, probably, the universe was already expanding, but it wasn't yet accelerating. I think the first part before you said, but it wasn't necessarily, I don't know that acceleration was part of the question, but I think you've provided additional beautiful detail while also answering the question. All right. Well, Alice is skilled in cross-examination, being a defense attorney. So let's pass it back to her and see if she has any follow-up questions for the witness. And please keep sending your questions, Alice. I love hearing from you. We do. Thank you, Daniel and Kelly, for your response. I'm surprised that the formation of the Milky Way was through collapsed stars and mergers and not from a collapsed disk. But it all makes sense after listening to your response. The Milky Way galaxy is not only very old, but it is older than our son. I truly did not know that, but I now have a better understanding of the formation of the Milky Way galaxy, and I am truly awed at its age and immensity. Thank you guys so much. That was super parable. Thanks. Where's the confidence? Where's the bravado? Come on, like this. I am Wolverine. Wait, I thought you were going to be Deadpool. Well, I am. I don't get it. Is your superpower disappointing me? Scan your pack to win heroic Marvel prizes. M&M's in Marvel. It's more fun together. See full terms and conditions when you scan. Okay, we're back and we're answering questions from listeners. Today, another question from a long time listener and many time questioner, Jane, with one of my favorite accents. Hi, Kelly. It's Jane again from the rather bracing red car in England. The other week, I was wandering along the beach and it made me think about shells. What are they? I remember being told as a child that if you took a muscle from its shell, it would die. But is this just because it's unprotected? Or is it an essential part of its life? A shell's like toenails. Useful. But you can live without them as we do if one is removed because it's ingrowing. Or are they like ribs, which I believe are essential for breathing? And am I right in thinking that shells aren't vascularized, which would make them more like toenails? I really do hope that you can help because listeners, they really do answer every question. Thank you, Kelly. Bye. All right. I also like Jane's sense of humor, so I look forward to hearing what she has to say when she responds here. So, snails! Snails are awesome. Let's just talk about snails for a second here before we get to their shells. Were you just waiting for somebody to write in and be like, Kelly, nerd out about snails? No, but I was excited when somebody did ask me to nerd out about snails because they are definitely awesome. I do feel like there's a lot of fascinating complexity here that I'm not aware of, so I'm also excited to understand snails better. Did you know that snails are in the same phylum as squids and octopuses and cuttlefish? Does that mean if I mean to snails, the octopi are going to crawl out of the ocean and enact revenge? I hope so. But I don't know. But they all have in common that they've got an identifiable head, a part called a foot, which is really just a muscular thing that helps them to get around. A visceral mass, which is where their organs are stored. When you look at an octopus and it's got that big head, you think, oh, that's probably its brain. It's got a big brain or something in there. No, that's its visceral mass. That's where the rest of its organs are. Its brain is a little part sort of near the eyes or whatever, and all the rest of the stuff in the head is visceral mass. That's where its testicles are. It's in its head. It's all up there in its head. I don't know why I picked texticles, but that's the first thing I imagined. Because there's a kind of octopus that has a part of its tentacle that can break off to deliver sperm inside the head of another octopus to the ovaries that are in there. Wow, I'm overwhelmed with information here. Yeah, I'm sorry. I'm going all over the place. I'm excited. Viseral mass. I'm stuck on this. What visceral means like you're feeling it? It's like really visceral. What does visceral mass mean? A viscera is another word for guts. So like if a feeling is really visceral, it hits you in the guts is how I think about it. I see. Now I understand that. And so you're saying the visceral mass is not where the thinking is happening. It's where the digestion and all that other stuff is happening. Yeah. And they also have a structure called a radula, which is a like, you know when a cat, when a little kitten licks you and you're like, oh, it's like I expected your tongue to be soft, but it's like it's covered in all these little hooks. Have you had that experience or do you cat? Yeah. Absolutely. You've been lucky enough to be looked by a cat. I had cats for most of my life before we had kids who were allergic and became dog people. Oh, I see. Well, it's good to be a dog person too. So they've got these like tongues that are really hard. And so like snails, for example, when they're like trying to eat a leaf, they keep rubbing this like really rough tongue on the leaf to like pull off pieces of the leaf and then sort of bring it into their mouths. And you can find like squids that will also like if they open up their beaks, their tongues will have these like radula, these like spiky, naily things on them that like help them pull stuff in. But I'm confused. Snails have tongues and beaks. They don't have beaks. Beaks are like a squidy sort of thing. Okay. But they do have like tongues. Where on the snail is the tongue? Like in the mouth. Okay. Where's the mouth on the snail? Okay. So if you're imagining a snail, there's like like an end where you see the tentacles. If you're imagining the kind of snail that I'm imagining, they do have little eye spots on the top of those to like help them detect light. They don't see much, but they can see like blurry outlines and shadows and stuff. But those tentacles are in fact coming out of their head and then sort of like towards the bottom, you've got like a mouth with a little tonguey thing. Wow. The whole snail seems so gooey. I just imagined the whole thing was a tongue. So now it's like you're telling me the tongue has a little tongue in it or something. No. No. All right. Daniel is learning basic biology on the show today. Well, that's good. And so, and there's a lot of mollusks species. So mollusks, that includes octopuses and squids. There's about 85,000 living species. But if you just hone in on the gastropods, which are like snails and slugs, there's about 60 to 70,000. So almost different species. Yeah. Yeah. So most of the mollusks are actually like snails and slugs, which you can find in the ocean. So actually most of these are marine species. Of course. And then you can find some on land and you can find some in freshwater, but most of them are marine. And in Red Car, England, how many different kinds of species of snails and slugs are there? In the United Kingdom, I found a number that there's 100 species of land snails and 46 species of terrestrial slugs. And are these widely different? Where like one of them is really huge and another one is super tiny? Or is this the kind of thing where like only a gastropod nerd is going to be able to tell these two species apart? I don't know in the United Kingdom in particular, but there is a huge amount of variety in snails. I mean, like, so there's giant land snails that weigh like, I think like two pounds. You can get like a really big one. I don't need any snails to exist that are that big, but they do. And then there you can get, you know, teeny tiny little snails. And then you can get snails with just absolutely beautiful shells. You think of like the most amazing thing you'd find on a beach that was probably made by a snail. And you might not think of it as a snail because it's beautiful. And I feel like I mostly think of snails as being those like land things that are not so beautiful. But what they're snails too. And a slug is just a snail that lost its shell. Oh, really? They're not a different species? Oh, no, no, sorry. They're different species. They lost their shell in an evolutionary sense. Oh, okay. So not like I pick up a snail, pluck off its shell and it becomes a slug. No, you would have killed it. Okay. Right. Because inside that shell is where they keep all of their organs. That's where like the visceral mass is. Let's jump ahead then to Jane's question, which is how does the shell get made? And so surrounding the organs is an organ called the mantle. And the mantle secretes the shell. So snails are born actually like in their eggs. They have teeny tiny little shells. Oh, they're cute, but they're soft. And so some of them will even like they hatch and then they'll eat the outside part of the egg to get the calcium carbonate to help start strengthening their shell. But so the shell grows. So like, okay, so you're imagining the part where the snail comes out. They grow from that edge outwards. And so as they're growing, that hole is getting bigger and bigger and bigger and it's sort of curving as it goes. And so if you look at a shell, the smallest whirl in the center is often like what the baby snail shell would have looked like. That's where it started its life. And then it got bigger and expanded over time. Does that make sense? Mm-hmm. Okay. And so how is it actually making it? They'll go to limestone to collect things like calcium carbonate and the mantle is just sort of secreting it out of the back and it's not vascularized. It's just like a hard structure that it's making by extracting stuff from its diet. Did you say it was eating rocks? It's like licking limestone? It's, you know, like we get calcium to make our bones from our diets and it gets it from its diet as well. There's calcium in a variety of different places and it could be licking limestone to get some calcium for a shell. So is it like a horse goes to lick salt because it needs it? Or is there like enough calcium normally in like leaves? Their diet probably is to some extent impacted by their need to get enough calcium to grow their shells. And actually the fact that you have to find the calcium to grow these shells is thought to be one of the reasons why sometimes gastropods will lose their shells over evolutionary time. So like it's a requirement that you have to get enough calcium to build this thing which sort of limits where you can go and what you can eat and stuff like that. And so it's thought that slugs are species where it just sort of didn't seem worth it to spend all of this time trying to get calcium carbonate. And so they have lost their shell. This is a fascinating little geological rabbit hole because isn't a lot of limestone made from ancient shells? Oh, is it like cannibalism separated by millennia? Sort of. It's like, you know, eating your own ancestors or something, right? Or it's like your ancestors have left a little deposit for you. They're like, oh, by the way, my great-great-great-grandkids are going to need this calcium. I'll just leave it here. It's like when your parents give you money to buy your first house, which does of course does not happen to everybody. It didn't happen to me. I bought my own house with my money. Me too. But anyway, yes, for people that that does happen to, it's sort of the same thing. Except many more generations removed. So yeah, so like when people say snails and slugs, it's not like there was one branch in the tree of life and snails went one way and slugs went another. There have been multiple different instances where species that had a shell split off and one path maybe kept their shell and another path lost the shell. And maybe they lost the shell because they were in a moist environment where they didn't need a shell that they could like curl up in to protect them from dry periods. Or there were less predators maybe or maybe there were lots of good hiding spots and the shell was just making it so you couldn't get in those hiding spots. And making the shell must have a cost, right? So if it's not providing a benefit, then it's going to be a net negative. Yep, exactly. Yeah. So I mean, the cost is not only that your diet to some extent is determined by your requirement to get enough calcium carbonate to make this shell, but also like now you're too big to get into certain hiding spots and you've got to carry this massive thing around. And so yeah, there are trade-offs for having a shell. And Jane was also wondering if these things are like tree rings. Like can you tell how old a snail is from looking at its shell? Not definitively. So for organisms like fish that live in really cold environments where there's also a warm summer, you get very clear differences in growth in the summer versus the winter. And those differences in growth show up as differences in like how things are laid down in a bone called the otolith, which is like their ear bone. And so when growth slows, the growth looks one way and then when growth speeds up, it looks a different way. And so you can look at those transitions to figure out how old the fish is. Does that make sense? And so the idea here would be that maybe snails are putting on growth in a way where you can like track the way that it grows to figure out how old they are. And the answer is it doesn't look like you can do that reliably for most of the species. And in fact, some species even reabsorb some of their shell and can like remodel it. And so that would really throw you off because it would be like, you know what, I'm going to erase the last five years and just kind of back up and then start over again. And that would be great. But no, it doesn't look like you can age them that way. Unfortunately. Jane also asked, is it like toenails? And it's kind of like toenails in that like it's not vascularized. And once it gets away from your cuticle, it's like if it got cut, it wouldn't necessarily hurt. But like if somebody ripped your nail off at the cuticle, that would really hurt and that would be bad. But for the snail, the equivalent would be like ripping off the covering for the organs. And so once all of their organs are exposed, they're goners. And so it would kill them. And you and Jane are both using this word vascularized, which I'm guessing means like does it get blood flow or something? Yeah, yeah, yeah. Essentially, is it already dead? Yeah. Yeah. And so I went to the Maryland Sheep and Wolf Festival. I promise this is sort of related. And they had an exhibit where they had ram horns that had been sort of like a ram had died and they cut off the horns. And at the base of the horn, when you cut it off from the skull, there's tons of openings at the bottom. And that's because a lot of the horn is vascularized. And so there's a bunch of blood vessels that go into a bunch of the horn. And if you feel the horn near the base of the head, it's warm because there's blood flow in there. But when you get to the end of it, it's cold because eventually the blood vessels don't go all the way. And so the tips of the growth are no longer vascularized. And vascularized just means has blood vessels in it supplying nutrients and stuff. Yeah. Okay. Okay. And I figured since there's like a sort of mathy connection to snails that you were going to ask me about chirality. Yes. And it turns out that most snails are right handed, which is to say that the opening opens to the right. To the right of what? Like? So I think it's like if you hold the snail in front of you, so the tip of the cone is pointing up on your right is going to be the opening. Oh, I see. Okay. Right. So you can define an axis and then the opening is either left handed or right handed relative to that axis. Yes. And so most of them are right and some of them are left. That's so weird how the universe seems to be right handed in some cases and left handed in others. Yeah. It's super weird. And I was listening to a podcast called Common Descent where they did like literally two hours on like the evolution of snails and shells and stuff. Wow. Which I thought was fascinating. And I learned that actually some snails like start their lives with one chirality and then they remodel and they end up the other chirality. And this happens like very early in their development. Why that happens? I don't know. Wow. Mysterious. Yeah. Maybe they're switching from the bad team to the good team. Yeah. Could be. Could be. Because some of these snails, if you happen to be born with the opposite chirality, you can't match up the body parts appropriately for baby making. And so you might be a little more lonely than you'd be otherwise. All right. But what have a whole other episode about how slugs and snails reproduce? I hear. Yes. We are hoping to get a guest on the show to tell us all about banana slugs in particular following another request from a listener. So hang tight for that crazy story. So if you haven't heard enough slime and goo on today's episode, don't worry. There's more on the way. There is never enough slime or goo if Kelly is around. That's my opinion. Jay and I hope we haven't talked too much about slime and goo, but you know, you sent the questions so probably you knew what you were getting. And let's hear what you have to think about the answer. And I hope this enhances your beach walks. Hey, Kelly, thank you so much for answering another question of mine. And it is my very great pleasure to let you enjoy my accent once more, Daniel. We don't have many snails on the beach here in Red Car. I think it's too cold for them. But I'm pleased to let you nerd out about them, Kelly. Your answer really hit me in the guts. That was so interesting, especially the bit about where snails get their shells. Glad for an opportunity for DKU bingo with cannibalism. So shells are more like tornels than bones, but removing them would certainly not be conducive to a comfortable existence. Thank you again. I will think of you both next time I wander on the beach. Keep being extraordinary. OK, thank you very much, everybody who sends in their questions. We'd love to engage with you. This podcast is not a lecture. It's a conversation with you. That means we want to hear from you. Please do write to us. Do questions at danielandkelly.org. Yep, we love hearing from you and I absolutely adore the rabbit holes that I get to go down depending on the questions that I get from y'all. So please send me down another fun rabbit hole at questions at danielandkelly.org. Do it. Thanks everybody for listening. Please go and do us a favor and rate the show on whatever podcast app you're using. It really helps people find us. Daniel and Kelly's Extraordinary Universe is edited by the amazing Matt Kesselman. He really is a wizard. You can also find us online on Blue Sky, Instagram and X, D&K Universe. Come engage with us. You can email us at questions at danielandkelly.org. We really do want to hear from you. And you can find our website www.danielandkelly.org where you'll also find the invitation to join our Discord where everybody comes and talks about the amazing Universe. And we also have the most amazing moderators. This is an I Heart podcast. Thanks for joining us. Switching to Virgin Media's lightning fast broadband is easy. We'll handle everything for you. That smooth broadband and smooth switching. Smooth like a walrus on a speedboat, powering through open, stewarded waters. Yeah, that smooth. Visit virginmedia.com. New customers only. Virgin Fibre areas, restrictions and credit checks apply. No set up fee, online only, terms apply. This is an I Heart podcast. 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