Science & Technology Q&A for Kids (and others) [Part 144]

Sa. Foreign. Hi, everyone. Welcome to another episode of Science and Technology, Q and A for kids and others. And I see a variety of questions here. Okay, there's one from Mouse asking, how rare was the recent New Jersey earthquake? How can we predict future earthquakes? Okay, let's start off with talking about what earthquakes are and then what we can. What can be done to predict earthquakes and so on. So the Earth has a liquid core and go down 50 miles. Well, it gets hotter and hotter. It gets hot quite quickly as you drill down into the Earth. But there's a kind of a discontinuity about 50 miles below the surface where the rock, instead of being solid, becomes liquid. It's very high viscosity liquid. It's not like it's something where you could pick it up and pour it. It's just very gradually liquid, so to speak. And the surface of the Earth consists of a collection of tectonic plates, which are big sections of the crust of the Earth that, like, for example, North America is mostly one plate, one tectonic plate. So it's kind of a. A big chunk of solid rock that's kind of floats on the surface of the mantle of the Earth, which is liquid, although, as I say, very, very highly viscous liquid. And there are places where more crust is being produced by sort of by upwelling of material from the mantle. And there are places where two plates are coming together, are being pushed down. The places where we see lots of mountains, volcanoes and so on being formed are places where these plates are, where there's more crust being produced and places where the plates are coming together and they're going down. Places where we don't see that. And so, for example, in the US The San Andreas fault is between a Pacific plate and the North American plate. And these are kind of two different pieces of sort of solid that are very large, thousands of miles across, that kind of float on the surface of the mantle. So what are earthquakes caused by? Earthquakes are caused by stresses that develop, and as a result of this plate motion, stresses that develop between these plates, where things, the. The two plates will slide relative to each other. Now, in fact, the basic phenomenon is if you have two solid things and they're kind of. You're trying to push them to slide, you'll find that you push, push, push, and nothing much happens. And then suddenly they'll start to slide. And they'll slide for a while, then they'll stop. So there are. What determines whether they slide is, is how much friction there is preventing them from sliding. And there's this concept of the coefficient of friction, which is if you have an object just sitting on a table or something, you push down on it with a certain force, you try and push it sideways. The amount of force that friction will kind of resist you pushing it sideways with is proportional to the amount of force you push it down with. And that constant of proportionality depends on the material. It depends on both the material that you have and the material that it's sitting on, so to speak. So if you have something that is, I don't know, on ice, for example, the coefficient of friction will be quite small. Things will slide easily. If you have something that's on a very rough surface, the coefficient of friction will be large and it will be very hard to slide it. But one feature of friction is that the force that's needed to start something sliding is larger than the force that's needed to keep the thing sliding. So what tends to happen? It's sort of a thing. If you, if you take a ruler or something, you put your fingers under, under two sides of it and you keep kind of moving them together, the ruler will, will sort of progressively slide on one side, then stop, slide on the other side, then stop. And that's the sort of stick slip behavior that's typical of the effect of forces being, and, and how, how friction reacts to those forces. So the same thing happens not just for a little ruler that you put on top of your fingers, but also for these giant plates of rock that are the tectonic plates on the, on the Earth. And so what's happening is, in an earthquake, what's, what's happened is that the, the, the, the plates, there's continuous stress on them because of the sort of overall production of more rock, larger pieces of plate, the subduction of plates back down to the mantle. There's sort of overall forces being exerted and between, on the boundaries between plates, there can be places where the forces are such that the things are led to try and slide relative to each other. But most of the time they're just stuck. They don't slide. Occasionally the force sort of accumulates to the point where suddenly they slip and then they'll stick again. That slip is what causes earthquakes to happen. That there's this moment when the rock, one plate, slips relative to the other and that slipping is kind of releasing lots of stress that existed in the rock that sort of been moving the rock to the right place again. And typically the slip starts at some particular place, the epicenter of the earthquake that can be Close to the surface, it can be deep underground. And that's kind of where the release of this kind of force, the stress that's built up in the rock starts to get released. So when an earthquake happens, the ground moves. In some places you can see where there has been kind of slippage between two plates and you can actually see kind of vegetation on one side. And it clearly was lined up with the other side before and it isn't anymore. I mean, the way this was all discovered in the. Oh, gosh, when was it? Early part of the 20th century was. People had noticed for years that if you take a map that kind of the coastline of Africa kind of fits into the coastline of South America. People had noticed that and said, oh, that's cool. And there was this theory that maybe there were plates that moved on the kind of surface of the Earth, that it had been the case that somehow Africa and South America were actually next to each other at some point in the past and moved apart. And that's why kind of the coastlines matched. And for a long time that was kind of a. Oh, that couldn't possibly be true. It must just be a coincidence type thing. And then eventually continental drift was discovered. It was something which, where. And these days one can even measure it explicitly, actually with. It's very slow, but you can measure it. I think you can even measure it with the aggregate of GPS signals from cell phones. At this point you can measure the tiny drift of different places, different plates relative to each other. I think some plates, like, I think the Indian plate, is moving quite quickly. And that's one where if you look at sort of projections of where it will be in the future, where it's been in the past, it's moved rapidly. Other plates are moving more slowly and one can sort of try and work backwards. What were the shape of how did the plates fit together in the distant past? And the general expectation is that in the past. Well, there's a thing often called pangea, which was sort of an aggregate of all the continents where there was sort of the whole landmass of the Earth was all clumped together. I'm not completely sure that that's an easy thing to extrapolate backwards because once everything was clumped together, it's like, well, maybe it wasn't clumped before that, but you wouldn't know that because you can, you know, work backwards and see it was all clumped and you can't really see what would have happened before that. You can get a certain amount of information about these things from magnetic, the, the, the magnetic field of the earth, which is changing a bit over time. But you can see which way was north when it, when a rock was formed. You can kind of, in some cases of some rocks, you kind of burn in the direction that the magnetic field was in at the time when the rock was formed. And so if you can tell, oh, you've got this rock in South America, this rock in Africa, and their norths would have pointed in the same place had those things been together. And now they sort of point differently. That's the way that you can tell that those rocks were at one time when they were formed, were together and subsequently moved apart. But so when it comes to where are there going to be earthquakes? Well, there are these plate boundaries and there's stress that builds up in these plate boundaries. And so then the question is, well, when's it going to slip? And it's hard to know. And there are a variety of ways people have tried to predict when it's going to slip. And for example, one thing is that there are certain electromagnetic effects that are thought to occur when rocks are under particularly high stress and so on. I mean, it has been claimed, I don't know if it's true, that various types of animals that may have better magnetic sensing capabilities than us humans, who probably don't have much magnetic sensing capability at all, that sense either magnetic fields or electric fields that are produced by the stresses that build up right before an earthquake. I don't know if that's really true, but it is pretty hard to predict when earthquakes are going to happen. People have been trying to do it for a long time. It's something where there can be sometimes four shocks where there start to be little tiny pieces of slippage, and then there's a big slip. Sometimes there are aftershocks, there's a big slip, and then there are later smaller slips. The amounts of energy released in an earthquake are really quite huge. And sort of what happens in an earthquake, the main. Well, so the ground slips by sometimes substantial amounts, like many feet and so on. And sometimes that's one thing. But the more important thing is at the moment when the earthquake happens, there's a whole bunch of kind of predictions, Pressure waves in the rock that get released. And they're really two kinds. They're ones that are kind of compression waves that are kind of like sound waves, except sound waves are in gases. And these are kind of sound like waves in rock where the rock is being compressed and expanding. Those are one type of wave. The other type of wave are shear waves where the surface of the. Where the energy is being sort of propagated by distortions in the surface of the Earth. I think the shear waves are much more damaging to buildings and things, but the shear waves also sort of arrive more slowly because, among other things, they have to go over the surface of the earth. And if you're going. The compression waves can go through the center, and so they have a shorter distance to go. To get across a circle, for example, you just can go across the diameter, whereas to get around the circumference, you. You're going kind of PI over two times as much as the distance across the middle. So about 1.57 or whatever times the distance. But the thing that. So what tends to happen in earthquakes is earthquake will happen. There will be these waves that get generated. They go, I think it's around 1,000 miles an hour. Maybe they go at different speeds, the compression waves and the shear waves. And so that's obviously much slower than the speed of light. So you can, for example, there are places in the world where earthquakes are expected where there's sort of warning systems that have sensors right on the fault. And then when you detect motion there, then you can at least let people know, shut down that factory or whatever else it is that might be really, really in bad shape if it got shook by the earthquake. I mean, in general, these days, buildings, it's always surprising to me that things like skyscrapers can survive being shaken at their base. But generally the principle is, if the material you've built something out of is if it bends, it'll be okay if it's shaken, if it's brittle and doesn't bend and just kind of is very rigid until the moment where it breaks, that's where you have trouble. And I think it's been sort of progressively learned. And there are also a bunch of things to do with counterweights in buildings that allow the base of the building to be shaken and to not cause more trouble. But I think in terms of the prediction of earthquakes, the. I, I don't think a huge amount of progress has been made in that. I think there are, you know, once the thing is happening, you can kind of. You can detect it. But I think in terms of. Of. Of knowing when it's going to happen beyond saying, well, there's stress building up. And I think there are various. Maybe there. I know people have talked about having better stress sensors for this. I mean, there also have been a whole variety of, can we prevent Earthquakes from happening by, like, pumping lubricants into the fault so that instead of having the stick slip behavior, as stress builds up, it gradually moves without having this kind of violent moment when it slips after it's been sticking for a while. I think that's one of those, you know, probably not an experiment to try, you know, in the San Francisco area to pump lots of oil into the fault and see what happens, because something bad might happen and it's kind of hard to predict what will happen. But I'm sure a bunch of people here have been in a variety of earthquakes. I've certainly been in a few reasonable sized earthquakes. And it's always, I mean, it's just surprising that the ground shakes the way it does. I remember one time, many, many years ago, I was riding a bicycle when an earthquake happened and I thought, you know, I'm, I'm must be losing it because I kind of lost my balance. And then I get into where I was going and people said, did you hear that? Feel that earthquake? I think another. Well, let's see. The, the. I mean, one thing to say about earthquakes is there's this whole idea, this thing called the Gutenberg Richter law, which relates the amount of motion to the total amount of energy released in earthquakes. And so when we'll talk about things like the size of the earthquake on the Richter scale, that scale is based on the amount of energy released in the earthquake and that energy. So it's a scale where every. Oh, gosh, what is it? Is it a factor of 10 or a factor of 6? I don't know a factor of 6, but it might be. It's a constant factor between a magnitude 5 earthquake, magnitude 6 earthquake, magnitude 7 earthquake. Each one is some amount, some multiple larger than the sort of previous number for earthquake size. And from that energy release, there tends to be a relationship to the amount of shaking that the ground does. And so one of the things that's important if you're building like a bridge or something and you have pylons for the bridge, is at what magnitude of earthquake does the amount of motion of the ground be such that the pylons will move too far apart and the sort of top of the bridge will collapse. And so one always has to be sort of thinking about what's the chance that an earthquake of a certain size will occur. And there's also a rule, there's another sort of power law rule which says the probability that an earthquake happens with a certain magnitude goes down as a power of the, of the magnitude of the earthquake. So the chance that at every, you know, every day there are, you know, magnitude, I don't know, three, two something or other earthquakes happening in all sorts of places around the world. Many of them are barely, you can barely feel. It becomes progressively rarer to have progressively larger magnitude earthquakes happen. And I don't remember the numbers here, but by the time you're at magnitude 9 or 10, they're very rare. And some of them are like once a century type rare kinds of events. And why is that rule? Why does that occur? Why is it the case that the more intense events are rarer at that particular rate? There are various theories, in fact some theories are based on some models that I made long ago for other purposes and there are various kinds of ideas about various. Well, it's a very common characteristic of so called critical phenomena that you get kind of a power law distribution. So what does that mean? Let me give an example. So let's imagine that you have something where you have, you're trying to decide is it going to be black or white. You're going to got a line of elements and they could be black or white. And what's happening is every time there's sort of a lump of black. This is hard to describe without a picture but essentially you're making kind of a V shaped piece of sort of droplet of black, a V shaped droplet of white. And when you have kind of an equal mixture of black and white, you end up with these kind of nested V shapes that are progressively larger as the sort of system can't quite decide am I going to become all black or all white. And it's kind of continually making this kind of tree like structure of nested black and white pieces. And that's kind of a typical thing that happens at so called critical points where there's sort of a, A, this, this kind of kind of tree like structure. And it turns out that when you have a structure like that you end up with well, what's the probability that you have a certain size of black blob versus white blob and so on. And you end up with these kind of parallel relationships. And it's claimed that earthquakes have this feature that they're somehow at this sort of often called some. Well, there's a, there's a version of this that I'm not sure is completely convincing, but there was a kind of a, a self organized criticality kind of concept. Another case where this happens again, not totally convincing but sort of interesting to look at is you have A pile of sand, and you're dropping, dropping grains of sand on the top of the pile. Every, the grains of sand will build up, will build up. Eventually the slope. As you build more grains of sand on top, the slope will be sufficiently high that you essentially, it can't support itself with that slope and you get a little avalanche and the sand starts. That starts rolling down the side. And so the question is, as you drop onto the top of the sand pile, eventually there have to be little avalanches happening. And eventually the end result of those avalanches is, is that the sandpile will have a certain angle of repose, as it's called. And the point is that these avalanches happen discreetly, much like earthquakes. Different, slightly different physics, different phenomenon, but similar kind of mathematics, essentially, or perhaps similar kind of mathematics that there are kind of these, these moments when sort of avalanches happen in the sand. And sort of the, the concept is there are kind of. That's similar to the way the sort of the slipping of plates happens to the point where it's kind of now sort of stable until more and more happens, like more and more grains of sand get put on and eventually there'll be this kind of violent avalanche that resets things. But it's not, it's not clear. I think it'd be fair to say that it's not really established how these things originate like that. Anyway, a little bit about earthquakes and how they work. Ah, comments on a live stream. The Sohail says the Indian subcontinent is moving very fast. It's increasing the height of Mount Everest by 6 centimeters every year. Yeah, because it's kind of crushing itself up against the Himalayas. And that's mountains are often formed, are usually formed when, maybe almost always formed when two plates collide and are pushing themselves up. Let's see. Prabhupada said, I wonder if digging for oil and fracking has any effect on the plates. Yeah, probably not. It's probably, you know, we humans have this habit of thinking we're having this big effect on things and somehow the effect is less than we expect. But certainly the main issue with, when you're trying to. Okay, so when oil is in rock, it tends to be in pores inside the rock. So the rock is porous and there's just oil in these pores. And one of the things you can try to do is to pump water down to try and push the, the oil up and try and also kind of open up the pores on the rock. Actually, strangely enough, I happened to do a piece of Kind of physics consulting for a oil related company back in the, oh gosh, in the early 1980s, studying before any of these, before any of these ideas really existed, doing simulations about what happened in porous rock and so on. I never knew what happened to that project that I did, but perhaps something terrible happened with it, I don't know. But it was interesting at least to learn about kind of the, kind of the physics of kind of mixtures of oil and water and porous rock and kind of some of the dynamics of what happens where you push water in and you say, well, I'm going to push the oil out. But that isn't what happens. Sometimes the water will just engulf the oil and it won't really pushing more water down. They won't really have any effect. And so it's kind of a detailed question where you have to do simulations and so on to find out what will happen for different porosities of rock, different kinds of amounts of different sort of empty space in the rock versus pieces of rock and so on to see what happens. The question here from Kathy, how do earthquakes cause tsunamis? So essentially what happens in a tsunami is just the ocean floor moves and if you've got a big volume of water and you just move it, then it's sort of inevitable. What, what's going to happen to the moved water? You know, you move the water up and you kind of pushing, you've got this kind of big lump of water that got moved higher than the other water. And so then the question is, well, what happens to that lump of water that got moved higher than the other water? Well, eventually the water will kind of find its level. That means the lump has to kind of somehow dissipate and you know, you've got a big lump somewhere in the, in the Indian Ocean or something. It's got to somehow spread itself out to the rest of the Indian Ocean. How does that happen? Well, turns out there are properties of the physics of waves on water. So roughly, okay, water waves, what's happening? In a typical water wave, there are different kinds of water waves depending more or less on their size and also on how deep the water is relative to how tall the wave is. But a pretty common form of ocean wave in the deep ocean is one where there's kind of a water, there's extra water somewhere and the extra water will kind of be trying to push outwards and then there'll be a dip and then that will lead to another. In the standard sort of way that waves are generated, there'll be something like a pendulum. You know, you pull a pendulum to one side, it will go, it will be fast in the middle and then it will go up the other side and it will keep going back and forth. It's the same kind of thing with the surface of the ocean. And if you looked at the individual water in those waves, the water is kind of going in circles. But the end result is that the surface of the water is going in these kind of big waves. If you look on like for example, on the surface of water, there are these surface waves that are associated with surface tension where the water is getting smoothed out by the surface tension. There are deep ocean waves. Well, okay, so there are different regimes. There are shallow waves where it matters that the water is kind of hitting the bottom of the ocean. That's what happens on beaches and things like that. You get these kind of shallow water waves in the deep ocean. It's really just an effect on the surface of the water. And it doesn't matter how deep the water is, you still get these waves. And each of these different kinds of waves has different speed, for example. And for instance, you can tell things about the speed of these waves. Well, okay, we can talk about wakes of ships and things like this, but let's talk more about how tsunamis work. So there's standard waves on the ocean and there's a swell on the ocean which is this kind of undulation of the surface. And in a tsunami, the water produces these so called solitary waves or solitons. Was an effect that was first observed I think in the 1830s by a chap, a British chap, who, maybe he was Scottish, actually that might still count as British. Who, oh my gosh, what was his name? I forget. Double barrel, very British sounding name who was riding his horse by the side of a canal and he noticed this kind of water wave that was just a solitary wave that just was kind of traveling along the canal with him. And I think in his paper, in those days people didn't write such stuffy academic papers. And he described something about how he kind of rode along with his horse at the speed of the wave and so on and followed it for quite a while. But anyway, that's an example of one of these so called solitons, solitary waves. And it turns out the physics of water allows for the possibility that you can have just sort of a single kind of solitary wave that will be quite stable on the surface of the ocean. It will just move across the ocean and without dissipating very much. And that's what, in tsunamis, that's what you end up with propagating out from the place where the earthquake happens. And the thing that is usually what's going on is that in the sort of deep ocean, those waves just cause a very tiny, maybe millimeters of height difference on the surface of the ocean. But a millimeter of height difference spread across a big area is a lot of water. And when that wave gets to a coastline, gets to a shore, then what happens is all that water is kind of piling up and when it arrives at the shore, that water just piles up and makes a giant wave that can go quite far in land and so on. And typically what happens is that again, you have to kind of see how the equations for the wave work and so on. But it will typically be the case that the water will kind of seem to be a giant tide that's going out and it's kind of like the water is being sucked back down into the ocean and then this giant volume of water comes up and causes all kinds of trouble. What's happened in the Pacific Ocean? For a long time there have been tsunami early warning systems. Now there are in the Indian Ocean as well. I happen to know that our fine technology gets used in building those, those particular things, at least a little Pacific. I don't know about the Indian Ocean, but that's a thing where once you know a tsunami is coming, they go fast in terms of the speed of things going across water, but slow compared to how fast you can communicate with radio or something like this. I mean, they're traveling at, I can't know how fast it is. I'm going to guess 200 miles an hour, but I'm not sure on the surface of the water. So it's, you know, it takes many hours to propagate across, across an ocean. Let's. Purpose commenting. Seems like studying underwater earthquakes versus those on land might be a good way to investigate lubrication of earthquake fault lines. I, I think not, because I think that I, I think in order to kind of get some lubricant into the fault, you have to kind of actively pump things in there. I don't think that any, you know, I don't think it's like, I don't think, although I'm not sure that it's like seawater is getting into the fault. I don't think that happens. But I have to say that it seems surprising because the pressure of water in deep ocean is very large. And it seems surprising that the pressure with which you can pump something kind of with an explicit pump is I would expect it to be actually smaller than the pressure in the deep ocean. Ah, somebody says the, the name of the chap. Okay, John Scott Russell. There we go. 1834. Right. So I was, I was right 1830 and I was right double barrel, British sounding name. John Scott Russell. I think he was a. He was one of the people involved in the whole iron steamship business. Was a big. Along with people like Brunel and so on. Was kind of a big. Engineering meets practicality meets kind of mathematical analysis and so on. Is can you build an ocean liner out of iron? And so on. All right, let's see. Well, Very different questions here. Let me see. Question from Risk here asking about the recent solar eclipse and what was learned from it. Well, I sort of committed myself to going to Austin, Texas to see this eclipse which at the last minute looked like a really bad bet because the weather was pretty overcast there. But fortunately it kind of cleared right before the eclipse. And actually it was kind of interesting to see kind of the eclipsed sun framed by clouds. It's different from the previous two total eclipses I've seen. So that was nice diversity. I was looking for this shadow band effect of the sort of shimmering of light that happens a couple of minutes before some total solar eclipses. I saw it in the 2017 eclipse. I didn't see it in this case, but somebody I know who was just maybe 20 miles away did see it and actually managed to get some kind of video of it. And I am now reminded that I was going to try and analyze that video. I, I did the most obvious image processing on that video and it didn't manage to pull out the kind of shadow band effect I had previously tried and other people have tried to take video of this effect and it's been rather hard to get video from it. And it's not even clear that kind of the way that the, the shimmering of light is produced is something that corresponds to sort of regular imaging of light that would be picked up by a camera as opposed to the way that our eyes detect things, which is similar to a camera but not exactly the same. But so that was, that was one phenomenon. Other than that I think I know people I know were were expecting to study some things about the ionosphere in the eclipse and I have not seen the results from that. So I'm more to learn about what happened there. Ask me again in a few weeks and I should have done my homework and learned what happened. Let's see There's a question here from Ithey, what causes Earth to have different biomes? So that's an interesting question. I mean, at the simplest level, the critters that are going to live in the Arctic are different than from the critters who are going to live on the equator. But there's obviously more to it than that. I think. I don't the. There are. There's different climates in different places caused by the local topography, caused by the way that the topography, the mountains that exist somewhere interact with the ocean that's nearby, interact with the ocean currents, which are very persistent over hundreds of years, maybe thousands of years, interact with other aspects of the environment. And those things produce different kind of local humidity, temperature, distribution of temperature, kinds of characteristics. And then there's a question of, well, as you change those characteristics, why do you get, for example, discrete changes from, oh, it's going to be a rainforest here to, it's going to be a desert here, and so on? Why isn't there just sort of a continuous gradation of kind of change of characteristics? I think it's not completely obvious, and I think it depends on things like speciation of organisms and so on that there'll be. It's kind of like, you might think, oh, you can just change a parameter in trees to go from a tree that likes sort of typical rainfall of this to a tree that likes a tiny bit different rainfall, tiny bit different rainfall and so on. But no, you get completely different trees that, you know, are like conifers in northern latitudes and, you know, tropical trees in tropical places and so on. And there are sort of discrete boundaries between these things. I'm not quite sure why that happens. I'm not sure that it's known why that happens. I mean, it's like asking the question about which a bit more is known about why there are discrete species that form in biological evolution. So it could be the case that there's, you know, you're between two organisms, that there will always be sort of continuous changes of those organisms. And. But instead it tends to be the case that you don't see the kind of. You might see these two different organisms maybe in the fossil record, and then there sort of seems to be a discrete change. There's no continuous gradation. There's enough continuity that you can say this thing probably was descended from that, but you still see discrete changes. Why does that happen? Well, at the lowest level, the way organisms are built is determined by their genomes, their genomes, as we've known for the last 70 years or so. Their genomes are discrete. They're made of a discrete sequence of bases in the DNA. A, C, G, T bases. That sequence of letters determines what organism will be built. It's the blueprint that determines the proteins that are going to get made. The proteins are the things that get assembled into most of what an organism is. But those genomes are long, billions of base pairs long. It varies with the organism. A simple virus might be tens of thousands of base pairs long, more complicated bacterium, maybe millions. And then by the time you're at humans, it's 6 billion and so on. And there are creatures, I think crabs and potatoes are two examples, and there's some other ones too, which have much longer genomes than humans, which might lead one to think they're more advanced species in some sense, but it's just because they kind of encode their information in a slightly different way. They make less, for example, those particular, I think crabs as an example use mostly A and T and not very much C and G in the encoding of their, in the encoding of their genomes. And so that requires them to have longer DNA to sort of encode the same amount of information. But so at the lowest level things are discrete, but there's a lot of discrete, there's billions of base pairs. So changing one base pair isn't typically going to have that much effect. I mean we all differ by, oh gosh, many millions of base pairs. I think we all have about 700,000 base pairs that are probably unique to us, that don't exist in any other human. And, and so there's, but nevertheless, the, while all humans are different, they're, except maybe identical twins. The, the, the, there's still many characteristics of humans which are in common across all humans. Even though there are all these small changes to the genome between humans, what tends to happen, it happens differently for organisms that have asexual reproduction from sexual reproduction. But what happens when there's sexual reproduction, for example, is this kind of reproductive isolation phenomenon where you have, you get to the point. So when you have sexual reproduction, what's happening in the genome is that you've got these two strands of DNA and in each parent sort of contributes a strand of DNA, and the final strand of DNA for the child is kind of a cut up version where it'll be first mother's genome for a stretch and then father's genome for a stretch, then mother's genome for a stretch and so on. And typically for humans, not sure what it's like for all Other species, but in our chromosomes and our sections of DNA, usually about five crossovers per chromosome. So that means there'll be a big stretch. You know, we each have a big stretch of our father's DNA, a big stretch of our mother's DNA and so on. Of course, the, the actual traits that are encoded on the DNA, they're not, it's not well engineered. I mean, the, the place that encodes eye color is probably all mixed up with the place that encodes, you know, finger length is all mixed up, which, with a place that encodes some feature of brain cells or something. It's not that the thing is laid out, oh, here's the, you know, the hair color section, here's the, you know, length of this section, and so on. It's all mixed up. And so the fact that there are only a limited number of crossovers per chromosome isn't really obvious. But any case, the thing that in sexual reproduction, the thing that happens is when, when two sort of, when, when things have evolved too far away, they no longer successfully mate either. It just, they don't sort of connect. They don't. Or the genomes that get produced are not, not compatible enough that they produce proteins that produce organisms that can actually survive. So that's sort of a mechanism for speciation, a mechanism for saying, well, this population over here of creatures that have long horns ends up getting more and more separated from the population of creatures over here that have fluffy tails or something. And I think the. So, and that ends up with this kind of the notion of discrete species that form, it's a lot less clear. Well, so a question would be, for example, there are probably about 10 million species that exist on the Earth today. A large fraction of them are things like beetles that live in the Amazon jungle. Things like this there seem to be in particularly in places like rainforests and so on. There seems to be apparently, I don't know really know this for sure, but people say there's a kind of high diversity of organisms, perhaps because there are many different sort of microclimates of different kinds of organisms that are fit for those, for those particular microclimates. And so that leads to just many more different kinds of organisms than exist in some place where there's sort of slightly more homogeneous climate. But I think this whole question of can you derive, why are there 10 million species? Nobody knows. And in terms of this isolation phenomenon, you might have species that were living on two different islands, for example, that very rarely meet up. And so then you can again have this Kind of isolation that will cause different species to be produced. That's what Charles Darwin originally observed in the Galapagos Islands with these types of finches, where on different islands the shapes of the beaks of the finches were different. And what he realized is they're different because there's different vegetation on these islands, which means that to be able to sort of peck out the thing you want to eat or whatever, you need to have a beak of a different shape to peck it out for different kinds of vegetation. And that was kind of the clue of, of this idea of natural selection that would sort of select for finches that have different shapes of beaks. Okay, but having, by the way, when it comes to asexual reproduction, it's less clear sort of how you get these discrete species, because each organism is just producing sort of progeny organism. In fact, I've just been doing some work which, as it happens, relates to this question of speciation and cases like that. And I think now have some understanding of how you get kind of many changes of genome eventually add up to a change in the actual morphology and the actual kind of structure of the organism that's produced. But when it comes to things like bacteria, there are often many. It's really much less clear what sort of species are like, although one can still identify very different kinds of bacteria. But they have all sorts of lateral transfers of genes and things like this that are more complicated than what happens in sort of the post Cambrian explosion, sexual reproduction period of biological history. But in any case, the original question here was why are there different biomes on the Earth? Why are there distinct biomes? Why is it not the case that there's sort of continuous variation from this to that? I think that's an interesting and difficult question because I think this, it really relates to this question of why is there speciation? And, you know, presumably at some level the reason is because you're trying to make a tree. A tree has certain kinds of ways it gets made. It has, you know, it has a trunk, it has bark that works a certain way, it has a certain respiration mechanism, works a certain way. And as you say, let's change these parameters, it may turn out that there just isn't a viable tree that can be made, given the sort of basic biology of trees in this intermediate case. And you kind of jump from one type of tree to another type of tree, and that's a discrete jump. Now, having said that, I do know examples that I actually studied myself where people might have thought that there were Discrete jumps in behavior. But actually there really aren't. So, for example, if you look up mollusk shells, if you. With. I don't even have one, but look at that. I actually have. Look at this. I actually get to do a demo of something because I can reach over and get an actual mollusk shell. Here we go. There's a mollusk happily sitting on my shelf there. So, you know, these mollusks grow in this kind of spiral shape. They start very small, they grow outwards, kind of one feature. You know, any organism has to have a sort of scheme by which it grows. And mollusks have a. Have a hard shell. And so if they're going to grow, if the organism inside is going to grow, it doesn't get to reform its shell from the inside. As the organism gets bigger, it has to kind of spiral outwards. But then the question is, well, how fast does it spiral outwards? And different, different mollusks. You know what I actually have. Wow. I get to actually maybe, maybe, maybe use a real demo here. I have some different mollusks here. Look at that. Okay, so there's a typical kind of spiraling mollusk. And as the spiral is different amount of spiraling, eventually you get these kind of bivalve shells which come from a spiral that's just much flatter than the ordinary spiral that's used in mollusks. And so the question is, if you look at different mollusks, I wonder if I have another. Well, let me see. I'm about to discover. I've got all kinds of mollusks here. This is a. This happens to be my, my collection of mollusks which came from studying mollusks. Let me see. Are there any other convenient. There's a good mollusk. Okay, here we go. There's a. There's a nice. If you can see that, that is a. A very pointy, very tightly wound spiral of mollusk. So the question is, the mollusks of the Earth, do they have a discrete set of possible shapes or is it kind of a continuous variation as you change the rate of growth, the rate of spiraling, the rate of kind of moving outwards on the spiral, and so on? And turns out, so far as I can tell, the all different parameter values are used by certain mollusks on the Earth. So from the very tightly wound to the very flat bivalve type shells and so on? And it's, it's. It's a. You might have thought that sort of the forces of evolution would cause there to be just discrete possible sort of tightnesses of winding and things like this. But that doesn't seem to be the case, it seems like all tightnesses of winding are used. But different mollusks with different shapes manage to live in different ways. So the very pointy ones can wedge themselves in rocks. And kind of just pick things up as they go by. The very flat ones live on the sand at the bottom of the ocean. They're, you know, all sorts of different shapes have different ways that they live. So it's almost as if biology kind of randomly picked the shape. And then the mollusks found out what it should do for a living, so to speak. Given given the sort of biological characteristics that it had. It then ended up with different sort of behavior for the organism. But somehow, then there's sort of the question of, well, if there are, you know, are there places where it's. It's all of this mollusk. And then. And then, you know, you go to a different place. And it's just a tiny bit different in sort of winding strength. And the mollusks will have different characteristics. So, for example, a very typical one for bigger organisms is you walk on four legs or two. And as you continuously change certain parameters of the skeleton. And the weight balance and things like this. You go from, well, you should be on four legs to you should be on two legs. Even though it's sort of a continuous change of the parameters. So it's a little bit unclear, I think, why you get. It's hard to explain why you get kind of these discrete changes. When it seems like many things are sort of continuously changing. There are many things that sort of geometrically have to be that way. For example, if you're doing well, even mollusks, for instance. The question of whether the thing ends up with being a single shell. Or a bivalve with two shells that link together. That depends on the geometry of the shell. And while when you've continuously changed the geometry. You go from something which is a single. You know, a single shell. To this pair of shell, pair of pieces, thing that. That happens at some point. Just like for leaves. I've also studied these a bit. The shapes of leaves. Depending on the precise growth rate and the angles and so on. You can either have a leaf that is just one big sort of simple leaf. Or you can have a leaf where there are lots of sort of crenulations and things in the leaf. And it kind of looks like an oak leaf or something like that. And as you change the parameters of the sort of angles and things. And the growth of the leaf. You can go continuously change the angles. But you discreetly change the geometry and so perhaps there are effects associated with kind of the discrete change of organisms that come essentially from matters of geometry, so to speak, or other kinds of sort of, in a sense formally derivable things. But so that would be my assumption. Now, once you have a biome, an ecosystem and so on forming, I think you end up with sort of the whole story of what eats what and so on, and all this notion of trophic levels and so on, where I think on, gosh, what is it on land it's maybe five or something levels, from the apex predator down to the little critters that get eaten by slightly bigger ones. I think in the ocean it tends to be many more levels, like a dozen or so. It's the big fish eat smaller fish type, type story. But that's another thing where once that's formed, once there's this sort of ecosystem that's formed, I suspect that's another place where there is some sort of discrete kind of an attractor, a way in which the system sort of initially can behave in a variety of different ways, but just by the dynamics of the system, it will be forced onto this kind of particular way of behaving, just like something that might be, you know, might wiggle around a bit and then there might be a single kind of circle that the thing goes on, which is kind of the stable orbit that the thing is pursuing, even if it's perturbed a bit. And that may be happening with different kinds of ecosystems, effectively. Let's see the question here about. Why is there only one species of human? What happens in Neanderthals? Yeah, well, I, that's another, you know, as, as Charles Darwin put it, in the, you know, struggle for life, so to speak, certain species survive. And what exact advantage we Homo sapiens had over the other hominids, homonyms, whatever, is I think still kind of a matter of debate. I mean, the Neanderthals were close enough to modern humans that they were certainly interbreeding and some characteristics. What is it? Is it blue eyes? Is it not blue eyes? I think it's. Blue eyes are supposed to be a trait that came from that species and still is preserved in humans today. I mean, I think many. There's slight variations in the percentage of Neanderthal DNA that we all have. A few percent, I think is a typical number. And so there are other sort of species, human like organisms. There's one that there's a few that might have survived until to historical times. What is it? Homo florensis, I think, is a Small kind of hobbit ish sized human that skeletons have been found in caves I think in Indonesia as the name might suggest. And it is what caused the other species of humans to not make it. I don't think we know. I think for Neanderthals they were well enough spread out, they certainly made artifacts. I think they made cave paintings. You know, can we say those cave paintings weren't as good as our cave paintings and so kind of they lost out? Or was it that the humans were better at modern humans were better at waging war against other folk or better at surviving the cold or better at. I don't know, it's not clear. I think the thing that tends to happen is there, there does tend to be a sort of. Well there clearly isn't a winner takes all because there are 10 million species. So it's not like there's this, this, this best possible form biology and it takes over everything that hasn't happened and precisely why it doesn't happen. That's a complicated question about speciation and so on that we don't really know a definitive answer to. But the question of it tends to be the case that one gets sort of in a particular ecological niche. There will be sort of a species of a different kind, of a particular kind. There'll be sort of a winner and non winners and I guess our, our branch of humans was the one that sort of won out in the struggle for life, you know, a few hundred thousand years ago. I think it's very hard to know. I mean in it would be, you know, you never know what's going to be discovered. You know, maybe there'll be Neanderthal writing discovered at some point and they'll be, you know, somebody will eventually have, you know, the great epic of the Neanderthal written describing some whole story that is either distinguishable from or quite indistinguishable from sort of early human kind of mythology or something like this? I think we just have no idea and it'd be interesting to know, but we don't. Let's see. I should probably wrap up soon because I need to. Okay, here's one that should be fairly straightforward. He says famous last words from robot. How do astronomers determine the composition of planets and stars that are light years away from us? Okay, basic thing is that when you have an atom of some chemical elements, hydrogen, helium, lithium, beryllium, whatever, any chemical element, the atoms of hydrogen are all basically the same. They could be different if they're different isotopes, have different numbers of neutrons in the nucleus. But basically all atoms of a particular isotope of hydrogen are the same. But when you. And they have a characteristic set of energy levels. So the electrons in the atom effectively can exist in a certain configuration, and then they can exist in a sequence of discrete other configurations. So the big discovery that was one of the early discoveries in quantum theory from about 120 years ago was this idea that there are sort of discrete possible states of a hydrogen atom. And so those discrete states correspond to sort of different configurations of the electrons or the electron in the hydrogen atom. And the what happens is if you get a hydrogen atom and you've been bashing it in some way, and it eventually gets into some excited state where it's not in its lowest energy configuration. It's a configuration where the electrons, the sort of electron cloud effectively has been distorted in a certain way that corresponds to higher energy. Then what happens is that will be the. As that sort of configuration makes a transition to a lower energy, it will emit a photon. It will take the energy that it had sort of bottled up in this electron configuration, and it will release it as a photon of light. But the point is that that photon of light is at a very specific energy that corresponds to the energy difference between that excited state of the atom and, let's say, the ground state of the atom. So any element has a certain characteristic set of so called spectral lines that correspond to the particular discrete energies of photons. Frequencies of photons, colors of photons, that's all equivalent that can be emitted by that type of atom. And so every different type of atom has that particular discrete spectrum of emissions. Same is true with molecules, Sometimes different frequency range, sometimes more in microwaves rather than visible light. But the first statement is you can tell kind of what elements are in a star by looking at the light from the star and looking at these spectral lines and seeing kind of which are they, the spectral lines for hydrogen, the spectral lines for helium, each atom has characteristically different spectral lines. Okay, it gets a little bit more complicated because the atoms are moving around because stars are hot. And that's. That causes these atoms to be moving often pretty quickly. The results of the atom moving quickly is that there is a Doppler shift. There's the kind of thing when you hear a siren go past you, it's higher pitched as it's coming towards you, it's lower pitched as it's going away from you. That phenomenon happens for light and that causes these spectral lines that were very precise energies to be slightly smeared out I mean, by the way, they're very precise energies which correspond to very precise frequencies. When the atoms involved are kind of at rest, not moving around. They're so precise that, for example, the standards of time and the definition of a second is actually based on the transition in cesium atoms, as it turns out, of particular kind of energy levels of a cesium atom. And that defines so precisely that that is a very precise amount of energy. That produces a very specific line in the kind of spectrum. In the distribution of colors of light that are produced by that element. So, anyway, there's some smearing out of spectral lines because of motion and so on. But basically there's a distinct set of spectral lines. That correspond to each particular element. The same is true when it comes to absorbing light. If you are looking at. If you have a gas, for example, and light is being shone through the gas, there will be at these particular frequencies where you can take, let's say, an atom in the ground state. And you can kick it to a particular excited state. That will correspond to the absorption of a very specific energy of photon. And so you get absorption lines as well as emission lines associated with gases and so on. So, okay, for a star, it's emitting light. And maybe it has some gas, some colder gas around the star that's absorbing light. And then you look at the spectral lines associated with these. And that tells you which elements are involved there. When it comes to planets, the big idea there is to see light from a star shining through the atmosphere, an exoplanet, for example. And being able to see that light which has had some of the light has been absorbed by the particular atoms or molecules that exist in the atmosphere of that planet. And so you're kind of looking both at the light that's emitted by the star. And the light that is being absorbed as it goes through the atmosphere of the exoplanet. And then we get to see that light. And we can kind of figure out from that. From which spectral lines occurred, an emission or absorption. What the material is of the star and the atmosphere of the exoplanet. When it comes to the surface of the exoplanet. I don't think we have any idea yet of what the sort of surface composition of exoplanets is. It hasn't yet been possible, I think, to directly image exoplanet. Usually exoplanets are discovered by things like you see a slight dimming of the star. Because the exoplanet has gone in front of the star. And it's blocking light from the star. You see a slight wobble in the star, the planet moves it. Things like this. I think knowing what the material is of a thing you're looking at is a tricky business. And I know, for example, Mars, it was very unclear what was on the surface just by looking at it through telescopes. In fact, for a while, people said in the late 1800s, people were saying, look, we can see canals being built on the surface of Mars. I think that might have been a vision defect of a particular astronomer, but it's also because canals were a big thing at that time on the Earth. And people are like, well, they've got to be Martians and they're probably very high tech, and so they're probably building canals. And we can see these giant canals. Well, turns out they weren't giant canals. But then later on people said, oh, we can see vegetation spreading during seasons on Mars. And that also turned out not to be true. And those were at best, sandstorms of various kinds. But that wasn't very obvious from just looking at it through a telescope. That's a hard thing to determine that way. Maybe there'll be some sort of clever technique invented for doing that. But now, now that seems pretty difficult to do. But things that are in gas, in the atmosphere of a planet are more doable by looking at transmission of light through that atmosphere. All right, I should probably wrap up there for today, but thanks for asking all sorts of interesting questions, and I see a bunch more that I would like to address another time. So thanks for joining me and bye for now.