There's Something in the Air - EWTS #013

Senan: Hello and welcome to Enough with the Science.

Joe: Welcome to another episode of our little science podcast. I'm Joe.

Senan: And I'm Senan and I feel, Joe, you're about to tell us what happens around here.

Joe: Yeah, well basically, if anybody's just fallen into our lap for the first time, welcome along to the podcast and we look at different science topics every week to enlighten my tiny mind about what is actually going on behind the stuff that's going on in the world. And so what's our magical topic today?

Senan: It's worse than Inception, there's things going on behind other things going on. I don't know, I don't care what today's topic is. Tell me a joke, I need to be cheered up.

Joe: Okay, why are there no parties on the moon?

Senan: Why are there no parties on the moon? Yes. What kind of party are we talking about?

Joe: You don't try and deconstruct the joke. You said tell you a joke, you go "Why?". Why are there no parties on the moon? The correct answer is; why are there no parties on the moon?

Senan: Why are there no parties on the moon?

Joe: Because it doesn't have any atmosphere. [laughter] Thank you.

Senan: You're a gas man.

Joe: Oh yes. We kind of led up to that. That was it. That's what we were working towards.

Senan: You are a gas... and you know, for our legions of international listeners we need to explain what that uniquely Irish phrase actually means.

Joe: Yes, not flatulent.

Senan: So if we were in England it might be; "He's an awfully funny chap."

Joe: You've been working on your accents.

Senan: But the reality is all of us are gas men and women because we wouldn't be able to do anything without the air that we breathe, the atmosphere that we have around the Earth. And that is the topic of today's podcast.

Joe: Way hey! We got there eventually. We got there eventually.

Senan: Took almost two minutes to develop that segue.

Joe: So yes, we're talking about the Earth's atmosphere.

Senan: The big question is why the hell do we have one in the first place? Our nearest neighbour, Mars, doesn't have one. Or at least the one it has is incredibly thin and useless as far as we're concerned.

Joe: So basically we're the only atmosphere in the solar system, are we?

Senan: Oh no, no, no. Venus has a hellish, much thicker atmosphere than ours. Titan, one of Saturn's moons, has a fine big atmosphere but let's just talk about our one. We could be here for several hours.

Joe: No, I would like to do an analysis of every...

Senan: With Venus, we will talk about it in a future podcast because it's an interesting kind of a planet; it's almost the same size as Earth. Anyway, why have we got one and Mars doesn't? Well, first of all, there's a size difference. So Earth is much bigger than Mars, has much more mass. And the more mass, the more stuff you have together in one ball in one place, the larger the gravity that it has. So it's able to... I mean the whole reason really that we have an atmosphere, leaving aside some other factors that I'll talk about in a minute, is that our gravity sucks that air down onto the surface and keeps it glued to the surface of the planet.

Joe: So anything that gets produced on the planet stays on the planet.

Senan: Within reason, yes. That would be, in a perfect solar system, that would be the case.

Joe: Wow, you have legal training. You've got legal training as well now?

Senan: There's a demon at the centre of our solar system; a double-edged sword that we call the sun. It gives us energy, it gives us light...

Joe: Suntans.

Senan: Suntans, which we might or might not want. And the other thing it does is it streams out a constant deluge of high energy particles; just out into all directions into the solar system. Those particles come and they hit molecules of air that form our atmosphere and it's a bit like a game of billiards where, you know, the cue ball hits another ball and it just causes the other ball to move away. The high energy particles coming from the sun are capable of stripping away our atmosphere; just kicking it off into deep space never to be seen again. And that effectively is what has happened to Mars. That is why Mars has no longer got much atmosphere to speak of. And certainly not one that could support life.

Joe: You say... you say... yes.

Senan: Well, in the past... there are some tantalising... now we're digressing here. There are some tantalising signs of past microbial life on Mars. Not proof, but there are some interesting signs. We'll come back to that because that is a fascinating... we could definitely fill an episode with that. Anyway, why hasn't that happened to us? It's because our planet has a magnetic field. Why have we got a magnetic field that Mars doesn't have?

Joe: I know the answer. Do you want me to tell you or is that a rhetorical question?

Senan: Fire away, yes.

Joe: There's a giant molten ball of iron at our core.

Senan: Well, it's not just iron but yes, the constituent we're concerned about is there's a lot of molten iron floating around in our core. And it's moving. Because it's molten, the heat... it's warm enough at the centre of the planet to keep that rock, which includes iron ore, liquid. And because it's liquid, it's moving around. There are convection currents causing that liquid rock to move around and the movement of iron generates magnetism. So that is how come we have a magnetic field. And that magnetic field extends outside the atmosphere into space all around the planet. And it forms a big deflector. So these charged particles coming from the sun, high energy but they also have electrical charge, and the electrical charge meets the magnetic field and it essentially diverts; the lines of magnetism divert a lot of those charged particles away from the Earth, around the Earth and then they float on past us.

Joe: It's a giant magnetic shield.

Senan: Yeah. And that is what is keeping our atmosphere from being stripped away by the solar wind.

Joe: So if the molten core decided for any reason, like in a terrible movie that I saw once, to stop rotating...

Senan: Yeah, our magnetic field would in all likelihood stop and then the sun's radiation would start to strip away the atmosphere. Now it might take a lot longer than it happened in Mars because Earth is much bigger and has stronger gravity. But it still would happen eventually. Now, the question is why is Earth so much hotter rather than Mars in the centre? Mars has cooled down. Its magnetic field doesn't exist anymore because its core has cooled down.

Joe: So it had a molten core at one point?

Senan: Oh we believe it did, yeah. We believe it did. Imagine you took a cannonball and a marble and you heated the two of them up in your oven until they were both at 100 degrees. And then you brought them out into your garden on a cold winter's day and you just left them on the ground. In a few minutes, the marble would have cooled down enough for you to pick it up; wouldn't burn you anymore, be lukewarm. The cannonball on the other hand; hours and hours before it would get cold enough. And that's kind of the difference; that's one of the key differences how we have held onto our heat whereas Mars lost it. But it's not the only reason.

Senan: There are radioactive elements mixed in with the melting core of our planet. And we have more of them than Mars has in its core because we formed in a denser part of the cloud of dust and gas that makes up the solar system... or that kind of became the solar system. We formed further in, basically, in a denser area. And so we have more radioactive elements in our core than Mars has and those radioactive elements are slowly decaying and like anything that's radioactive decay, it's producing heat. So they are helping to maintain the molten heat that's in there.

Senan: One last reason. A lot of people don't realise that way back after Earth formed, just after it formed, there was a huge collision. Another planet crashed into us. It's a planet that doesn't exist anymore because it became part of Earth. But we reckon it was about the size of Mars. Like a big, big planet that crashed into the Earth. And one of the side effects of that is the moon. So the debris obviously when that collision occurred, debris was flung all over the place. And some of that debris fell back into Earth and some of it formed a new thing that we call the moon. So the moon was actually formed by that collision. But that collision was so energetic that it added an awful lot of extra heat, energy in the form of heat, into our core. So our core effectively started out much hotter than the core of Mars because of this collision as well. So all these reasons mean that our core is still liquid because it's still hot enough to be liquid and thus we still have a magnetic field.

Joe: But at some undefined point in the distant future, the likelihood is that the core will run out of radioactive stuff and...

Senan: Yeah, I guess. I mean I don't know what the timescale is. You know, so we could...

Joe: Not this weekend, obviously.

Senan: So, I mean there's another thing probably going to happen that'll kill us first, or might, depending on what the time scale is.

Joe: You know I don't like any of our podcasts not to have, at least at one point we talk about the end of humankind.

Senan: And that is of course our sun will swell. When it reaches the end of its life it'll swell enormously and it will consume... it'll be bigger than the orbit of the Earth. So we'll become part of the sun eventually.

Joe: And will that happen all of a sudden or will we get like a couple of really good summers?

Senan: Oh I think we'll get millions of really good summers before that happens.

Joe: No, but like at the time when it decides to swell, is it like kind of something happens? No.

Senan: No, no, no. It's a slow... it'll swell gradually. No, no. And by then I feel sure that we will have developed faster-than-light space travel and we'll have colonised the galaxy and we won't be all that worried anymore about it.

Joe: You are such an optimist.

Senan: Well, one's got to... look, the glass has got to be half full. Better talk about what the atmosphere is actually made of.

Joe: Okay. What's in the atmosphere?

Senan: So we're going to talk about it in terms of the biggest constituents. It's a bit like reading the ingredients on something on a packet in the supermarket. They always mention the thing that's most first and then the less next and the next. We'll do it that way. Nitrogen. Nitrogen makes up 78% of the gas in our atmosphere.

Joe: And what's our recommended daily allowance of nitrogen?

Senan: Well, the particular form that nitrogen is in, in the atmosphere, is N2. In other words, that's two nitrogen atoms who have teamed up together and bonded to each other. It's an extremely stable form of nitrogen. What that means is it does not want to react with anything else really. Now, it reacts with some things barely, but for the most part, it doesn't really react with anything. And that is... where that came from is way, way, way back when the Earth was very young, it was covered in sediments that had nitrogen-rich compounds. So chemicals which contained nitrogen in them as one of their components, right? But the nitrogen in those chemicals wasn't free to become a gas. It was connected to other molecules or whatever in those sediments.

Senan: Then came along plate tectonics, which is this idea that we live on a thin crust of solid land that floats on top of a massive ball of lava. And it's actually divided up into plates; into separate plates that are floating on top of the lava. And gradually the edges of those plates bump into each other and one edge of one plate will go down underneath the other plate; whichever one is less dominant, we'll call it.

Joe: You know, it just occurred to me as you're explaining this in great detail that I can understand why some people believe that we're travelling through space on the back of a turtle. [laughter] Because it's just simpler. It's just... it's so complicated. Okay. Continue. Please.

Senan: Yeah, unfortunately the universe was not invented to be appreciated by our simple monkey minds.

Joe: It's not meant to be understood. This is our last podcast. We just realised the universe is not meant to be understood.

Senan: So, you've got these sediments containing nitrogen compounds that are slowly being sucked down into the lava by subducting under the edges of other plates, right? So now those compounds are going to be subjected to extreme heat and pressure by being in the lava. And that is going to effectively release the nitrogen from those compounds and allow it to become nitrogen gas. It's there in bubbles in the lava as N2; this form that's in our atmosphere. Eventually, some of that lava comes out of volcanoes. And that's how that nitrogen gets released. And because it doesn't really react with anything or with very little other things, it builds up. So over the millions and billions of years that the Earth has been in existence, it has been building up and not really being getting used up, which is why we have so much of it.

Senan: And when you breathe it in and you breathe it out again, it has no effect on your body. The only thing it's doing for you is it's diluting the oxygen because, believe it or not, even though oxygen is the part of the air that we need for life, too much of it is toxic. If you breathe 100% or even 80% oxygen, after a while you start to show symptoms of what's called oxygen toxicity and it'll eventually kill you if you're breathing it too long.

Joe: All right. Just poisonous.

Senan: Yeah, over long periods, yes. So like in hospital they might give you 100% or 80% oxygen for a short period of time because maybe your lungs aren't working properly or whatever. But they won't do it for a long period of time because after a while it starts to get toxic. So we do need that nitrogen to dilute the oxygen. And the other thing of course is oxygen supports burning. And the more oxygen you have, the more vigorous burning will take place. So if we had a very high concentration of oxygen in our atmosphere, like the whole planet would be a massive forest fire. Like, it would take one bolt of lightning to set the entire country on fire. So, it's good. We absolutely like nitrogen.

Senan: The only people who don't really like nitrogen are divers because of a thing called nitrogen narcosis. Divers go down below the surface of the waves; the deeper they go, the air that they're breathing has to be supplied to them at higher and higher pressure. Basically, they have to breathe air that's at the same pressure as the water surrounding them. And the deeper they go, the water pressure increases due to the weight of all the water that's above them, right?

Joe: Okay, so the tank is adjusting the pressure, is it?

Senan: Yes it is. And the reason for that is that if the air coming in from the scuba regulator was at a lower pressure than the surrounding water, your lungs would not be able to push against the pressure of the water to suck in the air. So in order to facilitate your lungs to be able to suck air in against that high-pressure water, the air has to be at the same high pressure.

Joe: God, I really don't want to know how they figured that out.

Senan: Jacques Cousteau, I think, is responsible for that one. So that means that the deeper a diver goes, the higher the pressure of what they're breathing. And nitrogen, as it turns out, becomes a narcotic above certain pressures. So normally here on the surface, we breathe it in, we breathe it out; no effect whatsoever. Once it reaches a certain pressure, it begins to have a narcotic—like drunkenness—effect on people. And I personally, when I was a young whipper snapper I did a lot of scuba diving and I did personally experience it on one occasion. One of the deeper dives I ever did; 44 metres if I'm not mistaken.

Joe: You get that into every conversation.

Senan: About how I went to 44 metres.

Joe: 44 metres. Must have been 44, was it?

Senan: Anyway, suddenly everything just looked wrong. Just... everything just looked... there was something wrong with how the world around me looked. And it's not because I was underwater.

Joe: Did it look like it was underwater? It didn't look like it was underwater?

Senan: But there was a peculiar sense of dislocation and nausea and just weirdness. It was almost like a drug trip.

Joe: And what did you do?

Senan: Oh I began to ascend and by the time I had gone up ten metres, the feeling had gone away. Like it was a very quick thing.

Joe: Oh you knew what it was though? You knew...

Senan: Oh yeah, when we were training to be divers, like we were taught about the potential for that to happen. And it's one of those things that it affects different people in different ways. And at different depths. Like I got affected by 44 metres on that particular day; another day if I'd gone to say 50 metres I mightn't have been affected. And some people mightn't feel it at all until they get to 60 metres. So it's a hugely different thing. But it is drunkenness and divers just forget about how to keep themselves safe with this narcotic effect and it's really dangerous. People have like taken out their regulator and offered it to a passing fish; that kind of thing.

Senan: Obviously for commercial divers, they have to go deeper than that sometimes. So a solution had to be found and what they breathe is a special, kind of artificial air that includes the same amount of oxygen—21% that's in normal air—but has helium instead of nitrogen. So the 78% part is helium. And that is completely inert in your body. You just breathe it in, breathe it out; no narcotic effect. So that's how they get around that problem.

Joe: But does it make you talk like Donald Duck?

Senan: It does make you talk like Donald Duck. Now that's not a biological interaction in the way that the nitrogen makes you drunk. That is just to do with the different density of the helium. So it's just your vocal cords when they work in a medium that's at a different density make a different sound to the normal sound we're used to making them here.

Joe: So let's go back above the waves.

Senan: So that's nitrogen; it's the main component. The next one is oxygen which I mentioned a moment ago is 21%. And it wasn't always there. We have actually evolution and microorganisms to thank for the presence of oxygen that we wouldn't have evolved without. Like a lot of our evolutionary ancestors; the creatures that we descended from; couldn't have evolved without oxygen. And we definitely need it because it's a very energetic molecule so it allows creatures who have a higher requirement for energy like us to actually evolve and exist.

Senan: Where did the oxygen come from? So two and a half billion years ago, something called cyanobacteria evolved and thrived. The oceans were full of it, the land was full of it. And how that made its living was it was able to make use of the sunlight that was beaming down on it from space and...

Joe: Thanks for clarifying that. As opposed to the sunlight from that comes out of some people's rear end.

Senan: Anyway, what it was doing is it was using that energy in the sunlight to split water. It wanted the hydrogen; so water is made from hydrogen and oxygen; it wanted the hydrogen because it could do something useful with it. It didn't want the oxygen so it just... the oxygen was waste product from the metabolism of that cyanobacteria. And there was so much of that cyanobacteria on the planet that it just released loads and loads and loads of oxygen.

Senan: But initially, that oxygen did not build up in the atmosphere. And the reason for that is oxygen loves to react with anything that wants to react with it. It's a very reactive molecule. And there was a load of iron-bearing rocks on the surface of the Earth at the time. And that iron hadn't rusted up until that point because you need; rust is iron oxide, so you need oxygen. So suddenly all of this exposed iron in the rocks; iron ore I suppose you'd call it; started to rust. And this went on for a long, long time because there was a load of exposed iron and it used up all that oxygen that was being produced.

Senan: And even now in the geological record, geologists can see this orange band; if you go down deep enough into the rocks that, you know, the deeper you go into the rocks it means the further back in time you're going geologically speaking. So the deeper down you go, you come to this orange band that is this rust belt that occurred when oxygen first started being created. Eventually, that phase came to an end when all of the available iron ore was oxidized and then the oxygen started to build up in the atmosphere. And even now, plants produce it as a byproduct that they don't want. So photosynthesis; the sunlight hits the plant and carbon dioxide... the plants use that sunlight energy to split carbon and oxygen from carbon dioxide that's in the air. The carbon it uses to build its structure; like the body of the plant, believe it or not, is made out of thin air; and the oxygen is something the plant doesn't want so throws it away.

Joe: So its byproduct is our fundamental...

Senan: Is fundamental to our needs, yeah. And to many, many other animals and even fish, you know, creatures in the sea; everything. So many things now require oxygen. It's amazing.

Joe: So that obviously... if you add 78% nitrogen to 21% oxygen you're nearly at 100, but you're not quite there yet.

Senan: There's something called Argon. It's known as a noble gas. Only 1% of the Earth's atmosphere is Argon. What does that mean, it's a noble gas? It means it really doesn't want to react with anything. So I said a minute ago that the nitrogen, the N2 that's in the air, doesn't react with many things; the Argon definitely doesn't react with anything. It's completely... it's an inert gas. Question is where does it come from?

Senan: So a lot of the rocks in Earth have an isotope of potassium called Potassium-40, which is radioactive. And like any radioactive substance, it is gradually decaying which means it's emitting some radiation, but also it is changing into a different element. So the fact that radioactive decay allows it to change and in the case of Potassium-40, it's changing into Argon gas. And that Argon gas is then gradually getting released, mostly from volcanoes. But it's a really like... there's very little. We're talking about tiny amounts now. But because the Argon doesn't react with anything, it has been building up.

Joe: So the Argon that's there is old?

Senan: Yeah. Like there's 1% now of the Earth's atmosphere. Come back in another three and a half billion years it might be 2% of the Earth's atmosphere. You know, so we're talking about a very slow seep. But it doesn't go anywhere.

Joe: It doesn't do anything.

Senan: It doesn't do anything, no, no.

Joe: Obviously we breathe it in and out and it has no effect on us.

Senan: No, no, no. I mean it's used for things like welding and some kinds of double-glazed windows use it in the middle gap between the two panes of glass and stuff. But there's no biological use of it.

Joe: Maybe you just haven't dived deep enough to get Argon drunk.

Senan: Maybe! But of course with that increasing pressure, other problems start to happen as you go deeper.

Joe: People just aren't as adventurous as they used to be.

Senan: I know, I know. People are just too careful about their own health these days.

Joe: Okay so how about Jason and the Argonauts? Come on. Come on. What is it? Argon... Argonauts...

Senan: Argon and Argonauts; derived from the same thing? I have no idea. I don't know never about that lore.

Joe: Yeah. I mean just... I thought you might.

Senan: Is that a Greek myth or is that a Marvel universe?

Joe: No that's a Greek... no that's definitely... I mean it's not Marvel universe. So maybe there was a place called Argo.

Senan: Maybe there was. Yeah. Perhaps maybe that's where Argon got its name.

Joe: Perhaps that's the first place they realised that like 2,000 years ago someone looked at a rock and went "That Potassium is decaying; let's call the gas Argon."

Senan: Why won't that gas do anything for us?

Joe: Trace gases.

Senan: Trace gases. Okay. So...

Joe: Hold on. Argon is 1%.

Senan: Argon is 1%.

Joe: Oh you're adding them up are you? Oh yeah.

Senan: I'm just keeping you honest.

Joe: The sums are not going to work out. I'm here to tell you now. There's over 100% stuff in the atmosphere. Over.

Senan: Right. The demon of climate change; Carbon Dioxide. Is a trace gas. There's actually very little of it in our atmosphere. 0.04%. That is one twenty-fifth of 1% of the atmosphere is Carbon Dioxide. It is part of the carbon cycle. So plants' respiration; they use it at some times. Other parts they don't... we breathe it out, animals breathe it out. So there's a cycle of natural use and production of carbon dioxide. And although we'll get onto greenhouse gases later... although it's kind of a demon in terms of, you know, too much of it is making our world warm up more than we want it to warm up; we actually need it. We need some. It's the right amount we need, not too much.

Joe: So it's not the ogre that maybe everybody... we can't just get rid of carbon dioxide.

Senan: No. The world would be a very different place if we got rid of carbon dioxide and we probably wouldn't be here to witness it either. Other trace gases; water vapor. So this is where the sums are going to go a little bit awry.

Joe: Yes they are. Because we're up to 99.024... 1... 6... 8...

Senan: Did you... you have a masters in maths don't you? Right, so the amount of water vapor in the atmosphere varies an awful lot depending on what part of the world it is, how warm it is, what the humidity is, blah blah blah. In some places there's none and in other places there's up to 4%. So the places where there's 4%...

Joe: Now we're 103%. There's 103% stuff in there.

Senan: Kind of makes a mockery of your sums.

Joe: Yes.

Senan: One would have to assume that all the other gases are in slightly lesser quantities in those places where there's 4% water vapor.

Joe: You wonder is it like... I mean 1% less oxygen would be a big deal. Wouldn't it?

Senan: Not necessarily, no. Not necessarily. I mean we have a bit of flexibility there probably four or five percent either side of the ideal 21%.

Joe: Well let's face it like if it's 90% humidity you're kind of not really going to be exerting yourself too much.

Senan: No, no. That's it yeah. That's it. So those are the main components. I mean there are some other greenhouse gases. When we get onto the section on greenhouse gases we'll talk about some other minor, tiny amounts of things that are there that are greenhouse gases. But those are the main ones anyway that we've spoken about.

Joe: Okay. So the composition.

Senan: Yeah. Now for our human convenience, we divide up the atmosphere into five layers on the basis of temperature. So it's... this is just a human thing. You can't actually find a border between each of these five layers. So starting at the ground; from the ground up until 12 kilometres you've got the Troposphere. This is where all the weather happens or at least any of the weather that affects us. And the temperature of the troposphere decreases as you move away from the ground. So the ground is warm and it warms the air above it, but the further away you get from the ground the colder it gets.

Joe: Is it... is it 1 degree per 100 metres? No. Is that...

Senan: That might be right. I can't... certainly from a hillwalking perspective that's a rule of thumb. You know, if you go up a mountain that's a kilometre high then you should be expecting a 10 degree drop of temperature at the top of the mountain.

Joe: No that never worked though. Not for 12 kilometres; should be minus... minus 1200 degrees! So okay.

Senan: Right. No, minus 120 I think.

Joe: I'm taking back that masters.

Senan: Okay.

Joe: I'm going to just stop doing maths.

Senan: Anyway, probably most of the mass of the air of our atmosphere is in that Troposphere and that's simply by virtue of the fact that gravity is stronger closer to the ground than it is further away from the ground. So most of the air gets pulled down closer to the ground. So the higher up you go the less dense the atmosphere becomes so the greater density of the air and the greater physical mass of the atmosphere is closer to the ground. And it's where convection happens, which is what causes our weather; most of our weather anyway. So that's air getting heated unevenly causes our weather.

Senan: If we move up we're into the Stratosphere which is from 12 until 50 kilometres. And counterintuitively, temperature actually gets hotter as you go higher in the Stratosphere.

Joe: That is weird.

Senan: Yeah, yeah. The bottom of the Stratosphere is 60 degrees colder than the top of the Stratosphere. Which is really weird. And the reason for it is ultraviolet radiation and ozone. So we're familiar with the ozone layer as the thing which protects us from ultraviolet radiation coming in from space. What is ozone? Right. The oxygen, the normal oxygen that we are breathing now in and out is O2. So two atoms of oxygen bound together into a pair. That's O2 and we're breathing it. Ozone is O3. It's three oxygen atoms bound.

Joe: It's one and a half O2s.

Senan: No it's three of them. It's one... oh yeah one and a half. Fair enough. One and a half O2s.

Joe: Maths! Boom! Back on the maths.

Senan: How does ozone get formed? So you've got high energy ultraviolet radiation coming in from the sunlight that hits the top of the atmosphere and it hits an oxygen, an O2 atom, and it's got enough energy to split apart the two atoms. So you've now got two singular atoms and those boys absolutely love to react with something. So they're hunting around looking for something else to react with; they bump into another O2 molecule and they say "Hey I'm going to react with you" and suddenly you've got an O3 molecule. So that's how ozone gets formed; by UV radiation coming in from space and breaking up O2.

Senan: The O3 is even better at absorbing UV radiation so that gets smashed apart and then it joins up with other O2 molecules and that's how ozone... there's kind of a conveyor belt of ozone getting produced all the time. And it has the handy byproduct of absorbing most of that ultraviolet radiation. Certainly the more higher energy stuff, the UVB and UVC band; most of that is getting absorbed. And otherwise it would damage our DNA, cause cancer, god knows what else down here. The UVA which is the lower energy stuff and some of the UVB gets through, gives us a tan, helps us to generate vitamin D and so on. Sunburn, you name it.

Joe: All the good stuff.

Senan: All the good stuff, yeah. So moving on up you have got the Mesosphere. A fairly... so that's from 50 to 85 kilometres in altitude above the ground. A fairly boring part of the sky. Coldest part; minus 90 degrees centigrade up there in the Mesosphere on average. But it's the place where meteors burn up. So meteors are just space rocks that have been flying around space since God was a boy and they're going at a ridiculously fast speed and...

Senan: Can I not say that? You gave me a funny look when I said God was a boy.

Senan: Well I don't know. Feel free to take it out.

Joe: You made him a boy. Might have been a girl. I'm not saying. I'm not judging.

Senan: Oh... no let's not open that. Anyway, so these rocks come into our atmosphere at crazy high speed. And eventually, they end up as being a shooting star because they burn up. But the reason they burn up is because friction; they're going so fast that when they hit the molecules of the air, the friction against the air molecules heats them up and they go on fire. The Mesosphere is where the air is thick enough for friction to happen. Above that the air is thinner and the most space rocks don't burn up any higher than the Mesosphere. Because the air...

Joe: But if the Mesosphere wasn't there they'd burn up in the Stratosphere anyway, wouldn't they?

Senan: Well yeah, the... some of the really big ones make it all the way down to the Earth. But not many. And those ones that do are called meteorites and they're worth money. So if you find one...

Joe: Wait, so it's a meteor if it burns up?

Senan: It's a meteor before it hits the ground. It only becomes a meteorite when it hits the ground. Yeah.

Joe: Everyday is a school day.

Senan: Yeah, there you go now.

Joe: This is becoming a science podcast.

Senan: Now we're very briefly going to jump through the last two layers because we're kind of running out of time here and I think we will be doing another episode on...

Joe: I think yeah, this is part one of a two-parter I think.

Senan: Yeah I think it's going to have to be, yeah. There's more to that empty air than you would believe. The next layer up is the Thermosphere; from 85 to 600 kilometres in altitude.

Joe: Okay.

Senan: What would you think... why is it got that name?

Joe: It's where you make coffee? Keep the coffee there? The thermos... Thermosphere.

Senan: The thermos peer. You're kind of... it is a temperature related word. You're kind of in the right... nothing to do with coffee but you're in the right neck of the woods. Believe it or not, the average temperature of the Thermosphere is 2,000 degrees Celsius.

Joe: I do believe it. Because you're telling me.

Senan: Isn't that pretty counterintuitive? How in god's name could part of our atmosphere be 2,000 degrees centigrade? And the weird thing about it is, let's say...

Joe: How big is it did you say again? It's...

Senan: From 85 up to 600 kilometres in altitude.

Joe: So 500 kilometres thick.

Senan: Yeah but pretty not very dense. Very... anyway...

Joe: It's not all... like it's only the top bit of it that is... like it's not 600 kilometres of two grand, 2,000 degrees?

Senan: Look, I wouldn't say the temperature distribution in it is homogeneous. So like I'm sure it's hotter at the top than is at the bottom but the average temperature in it is 2,000 degrees. However, if you were up there with your skin exposed, which would be a very bad idea for other reasons because you're pretty much in space at that point, you would not feel that heat. And the reason for that is because there are so few molecules of air in that part of the atmosphere that there's not enough... although those individual molecules might be at 2,000 degrees centigrade, you wouldn't feel it. There isn't enough of them.

Joe: So the actual place is not... like the molecules are that...

Senan: Well vacuum... the vacuum of space in between the molecules has not got a temperature of its own. But let me give you an analogy that might explain this; why you wouldn't feel it.

Joe: Well number one because I'm not going there.

Senan: Look, you shouldn't shy away from science. You know, unique scientific opportunities.

Joe: I'm... this is as science as I get. This podcast. I'm quite happy with this level of science.

Senan: Let's say you walk down the beach and there's a bit of wind and it picks up a single grain of sand and that sand hits you on the back of the hand. You're not going to notice that because a tiny little grain of sand. However, if the wind was to whip up 50 grains of sand and they all hit the back of your hand you sure as hell would notice that. So that's kind of an analogy for why you wouldn't feel the heat up there in the Thermosphere because there's so few molecules up there that even though they are at 2,000 degrees you won't know... there isn't enough of them for you to notice.

Senan: The big question that I'm sure you're only dying to ask is; how in god's name is that hot? How did it get to be that hot?

Joe: How did it get to be that hot? Thank you, Joe.

Senan: It's because of high energy X-rays coming from the sun. High energy... and other sources in space but mainly the sun. And also some of the high energy UV. It's hitting those sparse few molecules that are up there and it's imparting so much energy when it collides with those molecules that it's heating them up to that temperature of 2,000 degrees. Pretty amazing.

Senan: Couple of other interesting things about the Thermosphere. It's where the Aurora Borealis and the Aurora...

Joe: Say that again.

Senan: And the Aurora Australis occur.

Joe: Yeah stick to the Aurora Australis. The Borealis, you're butchering it. You're butchering the Borealis.

Senan: Anyway, that's where high energy particles from space interact... or from the sun actually... interact with the molecules in our atmosphere and makes them glow. And it's near the two poles because our magnetic field that we spoke about earlier funnels the glowing particles or funnels the energetic particles from the sun in towards the poles. So that's why it tends to appear in the polar region.

Senan: One other interesting fact about the Thermosphere; it's where the Karman Line exists. So the Karman Line is a...

Joe: Karmen.

Senan: Karman. K-A-R-M-A-N, yeah. Karman.

Joe: Oh okay, I thought it was like C-A-R-M-E-N. I was like...

Senan: Oh no, Carmen the opera? No. Karman. I'm sure named after somebody. It's 100 kilometres above the surface of the Earth. So barely into the Thermosphere which starts at 85 kilometres. It's the place where space officially starts. And the reason for that... the definition is; an aircraft, if it's well enough designed, can fly up to an altitude of 100 kilometres. The air is dense enough to hold it up. So under its wings, the air is dense enough to give it lift, okay? As it moves forward through the air. Once you go beyond 100 kilometres, there's no aircraft can stay up there. The air density is too low, the air is too thin. So if you want to stay up there above 100 kilometres you need to be in orbit. In other words you need to be going sideways at orbital velocity because the air won't hold you up.

Joe: So if you went up there in a plane you'd kind of drop back down until... like if you went over 100 kilometres you'd drop back under 100 kilometres and then you'd be able to fly and then you try and go up and then you drop back down again?

Senan: Something like that, yeah.

Joe: Or would you just explode?

Senan: Well I suppose if you got enough speed up that allowed you to rise, you'd shoot up out of the top and then you'd go in a ballistic trajectory back down underneath.

Joe: Like is that how... but those people who are doing like space tourists...

Senan: Yeah they are... well of course you're probably talking about the Blue Origin Jeff Bezos thing. That has no aerodynamic properties. That has no wings or anything, right? So they literally fire that thing up in a straight line with the rocket engines until it gets to 100 kilometres, they turn off the engines and it loops, falls back down. So but yeah those people are kind of going to like maybe 105 kilometres above the Earth just to get into space.

Senan: Very briefly because we really are out of time. The Exosphere is the furthest out band. Greater than 600 kilometres. It's... there's almost no air up there. There's like the odd molecule floating around that was part of our atmosphere once upon a time. And those ones in the Exosphere, a lot of them will just drift off into space. It's really... there's very little but it is just... if you had very sensitive equipment you could just about barely detect a bit of nitrogen and a bit of oxygen up there. So it is in theory part of our atmosphere even though it's more or less fully space.

Joe: And how big is the Exosphere? Is there a distance for the Exosphere?

Senan: I don't know. I mean if you could detect one oxygen molecule that had once been on the Earth and it was like way, way out past Mars, I mean...

Joe: Is that the Exosphere?

Senan: You know? So who knows where it stops.

Joe: Anyway, I think that's a good place to stop. So until you hear from these two Argonauts next week, it's goodbye from me.

Senan: And it's goodbye from me. We'll be back for part two of this the week after next. Cheers.