Daniel and Jorge Explain the UniverseDaniel and Jorge explore the deep, violent history of the Earth's surface.
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Hey Daniel, are your kids as tall as you.
Are yet yet? I've still got an inch on my fifteen year old, but he's already past my wife. How about you here, your kids taller than you are?
Not yet? But my son is taller than my wife now by a lot.
It's amazing that you never see them actually grow, and yet one day they're going to look down on us.
You mean physically, not figuratively. That's been happening for years for me. But at this rate they'll be there. Should be twice our height in about five years.
Right, definitely be twice as smart as we are. I mean, I'm already forgetting things faster than they're learning them.
I think my son is already smarter than me. Does that mean you've peaked in terms of your brain and your height?
Yeah? I think it's just downhill from here, and I'm really not looking forward to incontinental drift.
Wait, don't you mean continental drift?
No, I mean the inevitable drift into incontinents.
That would be earthshaken. Hi am orhamcartoonist and the author of Oliver's Great Big Universe.
Hi. I'm Daniel. I'm a particle physicist and a professor at UC Irvine, and I've eaten astronaut ice cream, but I've never worn astronaut underwear.
Why not haven't we all? Wait? Are you talking about use austronauts underwear or brand new Austronauts underwear No.
I'm talking about the kind that lets you drive cross country without having to stop for a rest break.
Oh you mean diapers. Wait, why are you bringing up astronaut underwear? Is that the topic of today's podcast?
No, today we're not talking about incontinents. We're talking about continents, which, weirdly are not the opposite of incontinence.
Yeah, that's the grammar for you, I guess. But anyways, welcome to our podcast. Daniel and Jorge Explained the Universe, a production of iHeartRadio.
Where we dig into the crazy motions of everything in the universe, things swirling around black holes, stuff flowing inside our own planet, and the particles moving between our toes. Physics in the end is about understand the movement of things, why they move, how they move, where they are going to move to, and we want to understand all of it.
Yeah. It is a motion filled universe full of things that are moving fast and things that are moving slow, which are all moving nonethe less, and it's up to us to try to catch those patterns and see why things are doing the things that they are doing.
And because we live a certain amount of time and our life happens at a certain speed, we tend to notice things that happen on our time scales, things that happen in seconds or days or maybe even years. But there's lots of things in the universe that happen on much shorter and much faster time scales. Quantum particles operated like ten to the negative twenty three seconds, and galaxies spend over hundreds of millions of years. So it's easy to overlook these very slow moving but very important processes, even though they literally shape our world.
Yeah. I guess we're used to like a certain rhythm of time, right, kind of like our brains maybe have a certain clock to them.
Yeah. Probably. And until recently, most humans lives were very similar to the lives of their parents and grandparents and great grandparents, right, Culture and technology moved so slowly that, you know, five thousand years ago, you could be pretty sure that your kid's life was going to be basically the same as yours. And you could imagine that life had been like this forever, that fast changes had never occurred, that the universe was basically static.
Yeah, it's amazing how fasting changed. I feel like within our lifetime the world has changed several times. Now, Like when I was growing out, we didn't even have email or cell phones.
Is that why you never got used to answering email?
Yeah, I haven't. I haven't picked up with that yet since I worked that. Fine, some things you don't have to learn.
We do live in a really fascinating era where we know that our kids' lives will be different from our lives and fundamental ways that we can't really anticipate. That's pretty exciting, but I think it also narrows our view and makes us focus on rapid changes in our environment. It makes it harder even to see the slow moving, big changes that frame everything around us.
Yeah. Almost like in this giant clockword of a universe, right with galaxy spinning and galaxy clusters churning and turning and planets spinning out there, it's kind of hard to notice that all of these things are happening, but they are happening, and there's a lot happening.
Yeah, And we tend to think about things out there in space happening sort of slowly on unstately time scales. But that's just because we're not used to thinking about things in terms of millions and millions of years. If you looked at a time lapse of the universe over billions of years, it would seem very chaotic, very dramatic to you. It would be turbulent, it'd be violent, it would be really impressive to watch. And the same thing happens not just out there in the universe, but also under our feet.
Yeah. I kind of have trouble thinking in terms of weeks or months. I'm more of a live by the day kind of person, live in the moment. What are you talking about again?
But as we piece together the story of how our planet got here, how our solar system formed, how the planets did their dance to end up in this configuration. Also see signs on Earth that there is a larger story to tell that things have not always looked the way that they do now.
Yeah, our planet is pretty big, at least compared to us, and it moves in pretty slow ways and in earth moving ways.
And by understanding how that works, we can hope to gain some understanding for whether it happens on other planets, and whether aliens out there also feel they're Earth moving beneath their.
Feet, yeah, and whether they live in the moment or if they think in terms of eons.
And whether they'll ever answer our email.
So to be on the podcast, we'll be asking the question what drives the movement of Earth's continents? It's not geographers or geologists, and I guess we're talking about the actual movement of earth continents, not like the people redrawing the lines of them or renaming them.
I'm pretty sure the maps follow the continents rather than the other way around. I don't think Earth checks our maps to decide where Asia is going to slide over to.
Oh yeah? Is there a clear line between Asia and Europe or is it political?
I think there actually is a division in the technic plates between them.
Mmmm.
Does that mean that there are countries that are in both continents? Clearly this is not a geography podcast.
There's a massive Eurasian plate that most of Europe and most of Asia is on. But like Saudi Arabia, for example, which is considered to be part of Asia, is on its own plate, and India is on its own plate as well.
So you're saying it is sort of like a subjective kind of or at least for some continents.
I think the definition of a continent is a little bit subjective. Yeah, but the definition of a continental plate these things are scientific and geological, like we can see where the edges are of these cracks in the crust.
You mean it's kind of leaky or definition, it's a little incontinent.
A little incontinent, exactly, all.
Right, Well, as you sure, we're wondering how many people out there had thought about the question of what drives the movement of earth technonic plates and continents? And so this time Daniel went out there into the wild of the UC Irvine campus ask people this question.
That's right, And today's episode is dedicated to TJ, a listener out there in recovery from a stroke who requested this topic specifically. So thanks very much everybody who answers these questions, and thanks to everybody in the USA irun campus who puts up with a weird physicist with a phone in their face.
So think about it for a second. What do you think drives the movement of Earth's continents? Here's what people have to say.
Do you know what makes the continents move the.
Ocean continents drift?
Yeah, probably because we have this plates, geological plates that are constantly moving.
But I'm not a geologist, so actually, to be honest.
I don't know it's not like because like the liquid and the earth, like the Earth center is still liquid and therefore, like the plates on top are like moving along because there's I'm not sure if there are currens going on, and that's why we are like plates are moving.
No, I'm not sure what it makes the continent's move. Do I know what causes the continents to drift?
I mean, they call it continental drift, but I don't know what started them moving.
Ah.
Yeah, so I understand that that is caused because the plates are sitting pretty much on molten rock, so one one across the other, they're kind of like crumpling, So that's what's moving.
The stuff that's on top right.
Well, I just I know that the molten rock is like revolving right inside the core.
That's about what I know. I don't understand more than that.
Tectonic plates.
Those are the plates. Why do they move? Magma movement? Anybody else?
I have no idea.
I agree, all right. It kind of seems like you took a lot of people by surprise, Like what are you doing? Why are you putting a microphone in my face? How do you approach people? By the way, Do you just walk up to them, or do you bring out the microphone later?
You know. The very first time I did it, I brought my kids with me so I would seem less weird and threatening, because I was expecting most people say no. But what I discovered is that most people say yes, no matter what. And so I walk up to them and I say, I'm a professor interested in what people know about some questions in science. Can I ask a random science question? And I think ninety ninety percent of the time people say, sure, no problem.
Hmmm. Interesting. I wonder if they think you're doing it for scientific purposes.
Aren't we isn't this part of science?
Or like, I mean, like you're running an experiment? Like anytime you open like ki, I'm a professor, I'm interested in They're probably thinking you're running an experiment.
Maybe I am. Maybe this whole podcast project is actually just an experiment. I'm writing up the paper right now. What's your hypothesis a physicist and a cartoonist can actually talk about science for five hundred episodes.
Sounds like a more of a there than an experiment there.
Implausible, I know.
But anyways, it's an interesting question. What drives a movement of Earth's continents because, first of all, I guess Earth's continents are moving. Maybe a lot of people don't know that they're moving.
Yeah, they are moving very very slowly, so slowly that it took us a long time to figure it out. And even once we had the idea, it took decades before people believed it because it seems like such a crazy notionh.
Yeah, it's pretty wild that a whole continent can move, and I guess it happens slower than anyone can notice in their lifetime, right.
You would think so, But actually the motion of the continents is pretty dramatic. I mean they move like centimeters per year, which is definitely something that you could measure. I think it just took a long time for people to wrap their minds around the idea that an entire continent could be floating on an ocean of liquid magma and sliding around the surface of the Earth. Is just so far from what anybody conceived of that the data really had to be screaming at us in our face before we figured it out.
Well, let's maybe one of you take us back and through the history of this idea. How do we actually know that the continents are moving, and when did we notice?
So around the turn of last century, like nineteen hundred, there were a bunch of unexplained phenomena things people couldn't figure out. They didn't have a story to tell that explained the stuff that they saw. And looking back, it seems sort of obvious because we know the answer. But remember that, you know, science is always running up against the boundary of our ignorre and there's always lots of random, weird ideas and pass not taken. So it's very easy to look back and see how the story came together. It's much harder when you're standing at the forefront of human ignorance to figure out what the clear path is. But basically, about one hundred years ago, we saw all these continuities between the continents, like connections between the continents that you couldn't explain if the continents really were separate and had always been separate. The most famous example is how the shapes of the continents are similar. You know, like the tip of South America the east coast matches pretty well Africa's west coast. Like you could just imagine sliding them together and they would like click together like puzzle pieces. There's lots of examples of that in many areas of research.
I mean they're sort of like jigs or puzzle pieces that seem to fit together.
So there's geographic continuities where the continents can fit together. And it's not just South America and Africa, like it's not too hard to imagine India and Antarctica and Australia like clicking together. But also if you look at the rocks on the shores of those continents, you see continuities, Like there are layers of rock you can see in Scotland and Ireland, and then you go to like Newfoundland across the Atlantic and you see the same layers of rock. It really looks like somebody you know, cut a cake and slid the two halves apart.
But I wonder if that's only a weird mystery if you don't look underwater, like it's only weird if you don't imagine that maybe that continuity continues onto the seafloor, Like did they check for that or did they just notice that it was the same.
The rocks under the sea floor definitely do not contain all those same layers, and the sea floor is mostly basalt, a different kind of rock, whereas on the continent it's mostly granite, So it's like different kinds of rock and definitely different layers, and you can really fit them together, like they find these layers on one continent and you can sign the same kind of rocks on the other side of the Atlantic. It really is very clear that these things click together in that.
Way, like in the way that they also match as jigsaw puzzle pieces.
Like the rocks in South America on the coast match the rocks on the coast of Africa the west coast. And there's other weird continuities, like there are fossils of animals that appear in South America and in Africa, and it's like very clearly the same animal that was one community, you find them across the Atlantic. So either you had like exactly the same animals evolve totally independently because the contents were always separate, or they used to be together the animals died a long time ago and then the continents split.
Or maybe there was a lost continent of a planets in the middle that was full of this animal. I mean, I just brainstorm me here.
Right right, Maybe it was ancient aliens.
Right yeah, there you go. No, but that's what I mean, Like I'm just trying to put my head in those in that time, Like could that have been a possibility for there to have been a bridge or something, or a continent in the middle of the tank.
Perhaps, But there's lots of different examples. It's not just like South America to Africa. Like this fossil evidence of this land reptile called Listrosaurus, which you see in Antarctica and in India and in Africa because those pieces used to click together. And then there's like fossils of this fern called Glysopteris, which is found in all the southern continents to show that they were once joined. And then there's this like fresh water reptile to Mesosaurus, which is connected from the south of Africa to the south of South America. So like one single bridge wouldn't do it. You need like a lot of bridges, or you just got to stick the continents together.
Hmmm. All right, So those were some clues, but were some other clues.
Another really fascinating clue was looking underwater. They did study the rocks on the seafloor, and what they found were these weird stripes of magnetism. Like the rocks on the sea floor sometimes contain this stuff called magnetite, which is very magnetic material, and it's influenced by the magnetic field of the Earth. And they looked the magnetic field of these rocks and they found this weird zebra striping, Like there's a stripe that's pointing one way, and then another stripe that's pointing the opposite way, and then another stripe that's pointing act the first way. So it's like the rocks have these alternating stripes of magnetic field sort of frozen into them.
They have like a pattern writ in the magnetism.
Yeah, they're like these zebra stripes, you know, like a stripe pointing towards the north pole, and then a stripe pouring towards a south pole, and then stripe pointing towards the north pole. So there are all these weird things that nobody could explain, all these weird clues that, like, you know, we couldn't tell a story that made sense of what we were seeing. The geographic clues, the geological cues, the biographic clues, the magnetic field clues, all of these things didn't make sense.
How wide were these stripes, like are they human size or are they like miles wide?
These things are not tiny, you know, they're like kilometers wide in some cases, but they show weird patterns. They're like not like exactly perfect stripes. They show some ridges and some twists, which we'll talk about later, but they're pretty big, I see.
So it was really kind of like there were all these puzzle pieces lying around in the table and like if you thought about it, you start to figure out then just the shapes can fit. But like the maybe, like the picture of the pattern in the puzzle pieces seemed to make sense if you spect them together.
Yeah, exactly. And it was nineteen twelve when a guy named Weggner first proposed this idea. He's like, I can explain all of these things with the simple idea that the continents were once all together, that they drifted apart. So he proposed this concept of Pangaea, that a couple one hundred million years ago, all the continents we know now were actually congealed into one big super continent and they've drifted apart over those years.
Like they were once part of a super band, but then they disbanded, and they of course they played rock music.
Exactly, And now we know actually that that's only the most recent example. Like Pangea existed around two hundred and fifty million years ago, but we reconstructed even further back into the past. There were super continents like a billion years ago and two billion years ago. It's really a crazy chaotic story. Pangaea is only the most recent super continent.
Whoa.
But at the time people were like, what your bonkers? How could the continents move? They're like these huge piles of rock. There's no way to like slide them around. You know, when you're doing a puzzle on a table, you have gaps between the pieces so you can slide them around. If all the pieces were like already stuck together, it'd be pretty hard to move them around to adjust their locations.
Yeah, I guess like the mechanism for how those continents are moving is kind of hard to fathom, right because the Earth we at least at the time, no, it's all made out of rock, right, even under the ocean it's rock, and so like, how do you move giant mountains exactly?
People knew that the Earth's crust was solid, and like fifty or so years ago, people had figured out that the Earth was solid underneath, it was very dense and it's probably liquid core. We actually talked about that in our episode about how to measure the gravitational constant. In order to do that, we basically had to measure the density of the Earth and understand that it was not like hollow, it was actually filled with rock. But yeah, the basic question is if you have a solid crust, even if it's liquid underneath, how do the pieces of the solid crust slide right like you have a balloon. It's filled with liquid, doesn't mean that like the surface of the balloon can slide around and rearrange the pieces right, There's no like room for things to move. So there was a lot of skepticism about this idea.
They thought it was crazy.
Yeah, and at the time that had an even more bonder sounding idea for like how mountains formed. Right now, of course we understand mountains form often when plates smash into each other, like the Himalayas are from India slamming into the Eurasian plate. At the time, they thought that mountains formed vertically as the planet was cooling. It was like shrinking as it was cooling, and things like bubbled.
Up mmm, sort of like shrink wrap. It was left after you shrink wrap something.
Yeah, exactly that It wasn't that mountains were rising, but that the rest of the surface was sort of like shrinking as the planet cooled, revealing these mountains.
Well, it sounds like today we know a little bit better, and so let's get into how these continents are actually able to move around the planet and what is powering this movement. But first, let's take a quick break.
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All right, we're asking the question what drives the movement of Earth's continents, and we talked about how they are moving and how we sort of figured that out because they are sort of like puzzle pieces. The continents, the shape of and also the rocks and the patterns on top of them are like a giant jigsaw puzzle, which I guess makes me ask a question, which is the corner piece, Daniel in a spherical puzzle? How do you even get started if you don't have corner pieces?
Antarctica? Always start with Antarctica.
But it's all white and it looks the same as the pieces in the North Pole.
Yeah, that's true.
It's a puzzle, but it sounds like we sort of figured it out. So we know that the continents are moving, and they have been moving, and before only about two hundred and something million years ago, all the continents that we know today were all crushed together into one super continent.
Yeah, around two hundred and fifty million years ago, And this was a really revolutionary idea at the time. This is an example science historians talk about a scientific revolution where the concept is intuitive and ingrained and widely accepted and then eventually overthrown by the data. You know that we're confronted with the facts and forced to change the way we think about the universe. And you know, people who talk about like science conspiracies and all this stuff. This is a great example of how science really does change when faced with the data. It takes a while, and it takes a lot of data. But scientists like to be right. They like to explain what we are seeing. I don't like to cover things up or engage in planet wide conspiracies. Everybody wants to be Wagoner, the guy who came up with a revolutionary idea that changed the way we think about the entire history of our planet.
Yeah. I think it's more like a Scientists like to prove others wrong.
Yo.
Yeah. Scientists are people, which means they're motivated by the same things people are motivated by, sometimes pettiness and sometimes glamor. Yeah.
And I think in this case you're saying like their motivation sort of aligns with the idea of finding out what the truth is exactly.
Scientists want to be right.
Yeah, they gain nothing by a worldwide conspiracy.
I mean, maybe we gain like cool robes and a secret handshake, but that doesn't seem to be worth it.
Yeah. Secret handshakes, Yeah.
Like pales in comparison to discovering the truth about the universe.
You just want to be part of the club.
I don't actually care about being part of the club. I just want to know the truth.
You just want to prove others wrong.
But in this case, it took like fifty years for people to really come around to this idea because there were a lot of puzzles before people figured out how it all worked. There were a few more pieces of evidence that started to sway people towards the direction of this idea. More things we learned about what was happening on the surface of the Earth that made the continental drift theory make more sense.
Yeah, And I guess it's not something that you can like test right or make a prediction about, right. It's not like you can see, like I think the continents are moving and in a hundred million years, this is what the Earth is going to look like, and you'll see I'll be right. You just kind of have to like look at the data and be convinced by the data, right.
Yeah. Actually, I think there is a prediction for what the continents are going to look like, and they put it up on a satellite orbiting the Earth. The idea being that if humans all die out and aliens come to visit in a hundred million years and find this satellite. It would be like evidence that we knew what we were doing or not.
I feel like that it's pretty risky. We could be totally off and then we'll be known throughout the Trinity in the cosmic community how wrong we were.
Yeah, that's why they died out because they failed to predict the continental drift erect.
Yeah, they couldn't even get that right, something as small as continent's moving.
Well, it's a really fun story because along the way we learned so much about our planet. One mental obstacle people had to accepting the idea of a continental drift was the idea of the age of the Earth. People had this concept that the Earth was pretty old, but the current thinking of the time was like the Earth was only around maybe ten million years old or so. They did this calculation to estimate how long it would take the Earth to cool from a ball of hot magma to its current temperature. And if you just think about like radiating heat out into space, then it only takes like a few tens of millions of years to cool the Earth down to where it is today. So the continental drift required a much older Earth, and that was hard to jibe with this idea that the Earth only takes a few tens of millions of years to cool.
Well, I guess maybe it depends on your theory or what you know about how the Earth started, Like did the Earth start with a bunch of molten rock or did it start with like free floating rocks then gathered and melted.
It started from pebbles and gas and dust and all this stuff in the very early solar system, which then formed gravitationally. But the gravitational pressure was pretty intense. I mean, it's intense enough to like spark fusion at the center of the Sun. It's not hot enough to get fusion going at the center of the Earth, but it's definitely hot enough to melt those rocks.
And so you're saying, like, that's how you assume. And if that's the only thing you assumed that was happening with a giant rock floating in space, then the Earth by now should have been you know, kind of.
Stone cold exactly. But around that same time, like the very end of the eighteen hundreds, very beginning of the nineteen hundreds, we discovered radioactivity like Becquerel left blob a uranium on a photographic place came back after the weekend, so it was fogged. The quires studied radioactivity was right around that time we understood it. So then people realized that radioactive decay inside the Earth was also keeping the Earth warm. The Earth is like a giant nuclear battery where these nuclear decays are heating up the Earth and keeping it toasty. So actually the Earth had to be much much older than just a few tens of millions of years to have cooled this much.
Well, let's talk about the continental driss then, I guess, how is it that the continents can move? Like, what's going on there? Are they not fixed in place? And what are they moving on top of?
So there's a lot of action happening at the edges of these continental plates. So like the Earth has a surface which is a crust we call it the lithosphere, and it's solid, but it's cracked into pieces, and at the edges stuff can happen. There's some places at the edges where they're being pushed apart. The plates are being pushed further apart. This is, for example, in the middle of the Atlantic Ocean. There's this ridge that was discovered in the nineteen forty where magma is bubbling up from within the Earth and pushing these two plates apart from each other, so the Atlantic Ocean is growing. That's one example of how we get like motion at the edges of these plates.
I think you're saying that, like the Earth, it's a little bit maybe like an egg right where it's like it's circular, it's round, but the inside, the outside is kind of hard and crusty, like a shell, and the inside is sort of soft and liquid in a way.
The inside is definitely hotter and softer. Just below the crust is the mantle, and the upper mantle is like technically a solid, but because it's under such great pressure, it can actually very slowly flow, and as you go further and further down, it gets to be more and more liquid. So yeah, things can slide and squish underneath the surface of the Earth. But one of the big questions was, you know, even if things are liquid, how do you get room to move? Right, Like, if the pieces are fixed in shape, then how do they move? And the answer is they're not fixed in shape. The plates both grow and shrink, so they grow on sides where there's like creation of new surface, like when you're creating new earth underneath the ocean, it's like magma is bubbling up and becoming a new surface. That's like extending the size of those plates. And then on the other side you actually have destruction of the plates, like the plates are going underneath each other, cycling back into the earth. So it's sort of like a very slow moving conveyor belt where you're destroying a plate on one side and creating more plate on the other side.
So, going back to our egg analogy, I think what you're saying is that, like the crust of the earth is not one whole piece like an eggshell. It's actually cracked in a lot of places. But then even if you crack it in breaking the shell into several pieces, you still have to wonder like how those pieces can move about. The reason is that they're sort of floating on semi liquid mantle right on rock that is fluid. And also they're not just doing that, but they're also sort of like being created and destroyed at the same time. These giant plates.
Exactly, each plate is like flowing in some direction on top of liquid, and where it hits another plate, it's being subducted it's like getting pushed down back into the earth. Those are like the deep trenches in the ocean, like the Baryanas Trench. In other places, on the west coast of South America and on the east coast of Asia, there are these deep trenches where the ocean floor is getting pushed down into the earth, and on the other side, new plate is being created, like the Mid Atlantic Ridge is creating new plates. So that's why, like the Atlantic Ocean is growing and the Pacific Ocean is shrinking.
Right, So like if you have one of these plates that let's say like you live in an island on top of one of these plates, and let's say the whole plate is flowing to the right, that means that like on the left side of your plate, there's more plate growing, right, there's like more of it, more of it coming up from the ground being created, pushing the whole plate to the right. But then on the right side of the plate, it's running into another plate and so then it's getting destroyed there or maybe my right. It's usually like one of them goes under.
Yeah, this subduction, so one of them goes under exactly where they meet, and we can tell where the edge of these plates are where the cracks are on the Earth's surface, because we can measure the seismic activity. Basically, there's earthquakes where these plates meet because they're grinding and sliding away from each other, or one is going under the other one, or there's like huge volcanoes underground creating new surface. And so if you look at like this seismic activity pattern, you just ask like, where are all micro earthquakes on the Earth. Then they don't just happen randomly all over the Earth. They happen in these lines. If you put a dot on the Earth wherever there's an earthquake, that come out to make these patterns that show you the edges of the plates, like the cracks in the eggshell.
You can hear the continents crunching. Kind of.
Yeah, it's actually interesting bit of history. In like the nineteen sixties, the US and the USSR, we're doing underground testing of nuclear weapons. And one of the best ways to detect underground t testing is to build a worldwise network of seismographs to see when testing is happening. And so that's why the US invested in a huge network of these seismographs, and that's one of the ways that we learned about all these micro earthquakes that showed us where the plates were.
Mmmmm, like we're paranoid, but then we used that for sign.
Well. As usual, the science budget is a tiny, tiny fraction of like the military budget or the intelligence budget, or even like the consumer electronics budget. So we're always trying to be clever in ways to like leverage the huge resources of other sectors the economy for the benefit of science.
I think you can also tell where these plates meet by looking at more volcanoes, right, Like most volcanoes are where two plates intersect.
Exactly earthquakes and volcanoes. And if you look underwater at the Atlantic, you can see this huge ridge which is basically a line of volcanoes where the Earth is cracked and it's seeping up, and that magma then becomes new surface of the ocean. And that actually explains what's going on with the magnetic striping, because this new rock is forming and cooling, but it's happening over time, and so as you get further from this mid Atlantic ridge, the rock gets older and older. So what the rocks are doing are tracking the Earth's magnetic field over time. I remember the Earth's magnetic field is not constant. The North Pole today is not where the North Pole has always been, and over the last millions of years it has flipped a bunch of times. So basically this magnetic striping is a record of the flipping of Earth's magnetic field because it's like influenced by the magnetic field and locks in whatever it was at the time, and then it doesn't change.
Hmmm. It's like the Earth's magnetic field paints on these rocks sort of right, and so as new rocks are coming up, they get painted differently, and it logs how many times Santa Claus had to move over the years, which is probably a big pain for him and Missus Claus.
Yeah, but it's a silver fascinating like measurement of the history of the Earth. It's like rings on a tree, right, It like tells you how many times this has happened. And because these things are not perfect stripes, you can use them to reconstruct how the ocean floor has grown, right, it tells you, like where it's grown faster and where it's grown slower. You should totally google a picture of the magnetic field striping of the Atlantic. It's really fascinating. They've used this to reconstruct like the super continents a billion years ago and two billion years ago. It tells you the whole history, the dramatic, violent history of the continents on the surface.
Yeah, it's pretty dramatic. I guess if you look at it from a long term point of view, right, like if you were to take a movie of the Earth and fast forward it, you know, by millions of years, you would see these giant continents like crashing to each other and split apart.
Yeah. But the surprising thing to me is that it's not that slow. It moves in centimeters per year. In some places, it's like eleven centimeters per year of subduction. I mean, that's not so tiny. Like if your neighbor's house moved closer to your house by centimeters per year, it wouldn't take very many years before you.
Notice, unless you really like your neighbors and are considering moving in with them. But I think the question that was posted originally was what drives the movement of these continents, and so like the question is like why are they moving anyways? Like we know how they're moving. We talked about the mechanism that makes the move, but like, why are they moving? Is maybe the question, and so let's get into that big question what drives these continental shifts and drifts. But first, let's take another quick break.
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All right, we're asking the question what is making Earth's continents move? Because they're moving, and they're moving none of us insignificant rate a few centimeters a year, which doesn't seem like a lot, but over millions of years, it can make continents split apart, crash into each other, make new continents. It's pretty dramatic and juicy history there that the Earth has. And so now we're asking the question, what is making these big continental motions, what is powering it? And why isn't the Earth just staying the same.
Yeah, it's really amazing how the surface of the Earth reveals what's going on underneath. Beneath the hard crust, this cracked eggshell of a surface of the Earth is a crazy amount of energy of heat and motion of the mantle. So we have the outer mantle which is pretty solid but actually does flow but blow that things get liquid, and what's happening there is convection, like things heat up and so they rise, things cool down and so they sink. It's sort of like a big bubbling pot of tomato sauce where you have like bubbles coming up and things sinking and things are mixing. Right when you have soup bubbling on the stove. It doesn't just sit there like mixes itself. Because things rise, they get hot and sink as they cool. And that same thing is happening inside the Earth, creating these convection cells, which are basically huge spinning currents of magma underneath the Earth that drive the conveyor belt on the surface.
I guess it pushes like it creates like let's say, a giant flow forms or giant bubble forms in the Earth center. That's going to put pressure on the mantle, which is then creating pressure on the eggshell crust. Right.
So imagine beneath the center of the Atlantic, for example, there's a hot spot, and so magma gets extra heated there and what happens, Well, it's going to rise and it's going to bubble up, and there's a crack there between the tectonic plates, so it's going to come out, and so it's pushing those plates apart. And on the other side the subduction where the plates are meeting and banging into each other and getting pushed below, those are cooler, right, and so as that cooler surface gets pushed into the magma, it falls, it sinks, right, because it's cooler, cold things sink and hot things rise. So now you get this circular pattern, cold things sinking on the edge of it, hot things rising in the middle.
So then all of that energy that's moving the continent comes from the energy kind of boiling under the surface of the Earth exactly.
And there's lots of really interesting questions there, Like for a long time people thought that the dominant force was the seafloor spreading, that this bubbling up of the heat was really driving it, and it was like pushing the plates and it was crunching them together, and the subduction was really just like the plates getting slammed together ultimately from the seafloor spreading. That was like the dominant idea for the first few decades after the whole concept of plate technonics was accepted, but more recently people have been convinced of the opposite, that it's the subduction that's actually dominant, that's the crunching of plates and pulling them underneath that's really making it happen. That it's more of a pull than a push.
Like people thought that what was driving the movement was the new land being created pushing the plates outwards, but you're saying it's more like maybe it's where they're dipping underneath the surface that's actually pulling the whole continent away, and then where there's a crack left, then new ground gets formed there.
Yeah, exactly, And that sort of makes more sense because the surface is not that solid, so like what it's easier to do to pull a carpet or to push on a carpet, So pulling like at the edges of the plates sort of makes a little bit more sense to me. But it's really a question of like energy dynamics and force balancing. Where is this really happening? And you know, one of the deepest questions is like why do you get these convective cells in the first place, How do these cells get started? How many are there, what is their structure. It's like we'd like to understand the boiling tomato soup that's underneath the surface of the Earth.
And I think some of this boiling is also what makes the Earth's magnetic field too, isn't it.
The Earth's magnetic field is definitely connected to the flow of all this stuff inside the Earth. We don't understand how much is connected to like the mantle or the outer core, which is a little bit more metallic, but definitely we need flow inside the Earth to generate the magnetic field. And it's an interesting connection, right because the magnetic field also flips and that leaves a pattern on the seafloor. So the whole thing is like a big, complicated, beautiful dance.
Hmmm, the earth shuffle. But then I guess a question that you can ask is like how long is that going to keep going? Like is the Earth going to run out of you know, inner boil, Is it going to run out of energy inside? And then everything's going to just stay still.
The Earth will eventually cool, right. This depends on the Earth maintaining its temperature. And while the radioactive decay inside the Earth is keeping us warm like a nice battery, it's not enough. We are radiating more heat out into space than it's being generated by those decays. So they think, like, in about a billion and a half years, the temperature of the mantle won't be high enough anymore for this kind of flow, and we think the place tectonics will cease. So we got like another billion and a half years.
A billion and a half years before the crust kind of freezes in place. Right whatever, What we look like then is how we're going to look like until the end of time, or at least until the Sun eatses up.
It's like another billion years of musical chairs and then eventually the music just stops.
Now, is that heat from the center of the Earth significant, Like, are we going to freeze or does? Right?
Now?
A lot of our heat comes from the Sun.
The temperature of the surface of the Earth is not too affected by what's going on inside the Earth. That's more dominated by the Sun and the atmosphere and those kind of effects. So even if the Earth's continents do freeze in place, we can stay warm from the Sun. That's not an issue.
Maybe a bigger issue by them will be that we won't have a magnetic field.
Right yeah, where the Sun is getting brighter and brighter, so we're probably just going to overheat. In a billion years, the Sun is going to be significantly brighter than it is today.
And we've seen this kind of thing happen in other planets do right Well.
Earth is the only planet in the Solar System with active tectonic plates. We think there's evidence that the Moon and Mars both once had tectonic activity, though they are smaller than the Earth and they cool faster, and so both of them are basically already frozen in place.
Well, there aren't that many rocky planets to begin with. There's like three or four, right.
Yeah, But they're also rocky moons, right like Ganymede and Io. These are planets, they're geologically active, but we don't see tectonic plates on them either. You need like just the right mix of temperature and also water. Like water is really crucial to making this happen because it weakens the crust when the rocks are cooling. If there's water around, it changes the chemical composition of it, which makes the crust a little weaker, which allows for this sort of like conveyor built destruction and subduction. For example, Venus is still internally hot. We think there's like oceans of magma inside, but doesn't have tectonic plates the same way Earth does. And we think that probably it's because it lacks water. It doesn't have any surface oceans to make this happen.
Yeah, it's just read about this. Water actually makes rock melt at a lower.
Temperature, right, Yeah, so it encourages the flow, right. Essentially, it weakens the rock and makes it more liquid. So the fact that we have oceans and tectonic plates is not a coincidence. You need really both of those things to happen. Venus is a crazy planet anyway. They think like a billion years ago there was a complete volcanic resurfacing, meaning volcanoes completely created a new surface of the planet basically just by spewing magma everywhere. But we don't think there are plate tectonics on Venus.
Mmm, weird. Interesting now, And you said this happens in moons like our moon. But then also other moons in other planets.
Yeah, so the our moon probably had plate tectonics in the past, but now it's cooled. Io, which is one of the moons of Jupiter, and it's about the same size as our moon, is still actively volcanic, Like the voyager saw several volcanic plumes rising like hundreds of kilometers above the surface. So there's definitely stuff going on inside there, and it's probably mostly due to like thermal energy from tidales from Jupiter, which produces like convection in the interior of Io. It's like getting squeezed by Jupiter's gravity. But we haven't actually seen plate tectonics on Io as well, though, you know, Io has not been studied in great depth yet, so.
It seems like it's kind of rare to have plate tectonics. Or is it just that the other planets had it but then they stop.
It might be both. It might not be an automatic thing for every planet to have it. You need the right combination of temperature and convection underneath the surface and water on the surface to weaken the crust. So it doesn't happen all the time. But you know, if it happened on the Moon and on Mars and on Earth. That means it's not super duper rare. Another question is like, well, how important is it? Does it really matter if you have plate tectonics. It's kind of fascinating on Earth that the continent's drifting apart changes the evolution of animals because if like a community gets split in half, now you have two of them isolated and they can evolve in separate directions. We don't know, like what would have been the history of life on Earth if we didn't have plate tectonics. It might be very very different.
Mm we wouldn't have kangaroos for example.
Right, Sometimes it's important to have an isolated community so they have times developed some new capacity before they have to compete with the mainland. This is called like biogeographic islands and communities. It's a whole field of study. It's actually replicated and really interestingly in artificial intelligence. Sometimes when you're training neural networks and you give them a hard new task, you create like a subpool of these neural networks, so they train on this hard new task in isolation before they have to come back and compete with the other neural networks on the mainland. So you know, having islands and having divisions between these things can be really helpful for creating diversity and weirdness in life on Earth.
I guess it can affect life, but is it necessary to life?
Fascinating question. I wish we knew the answer to. The only way to really figure that out is to see a bunch of other planets. So we're not there yet, but people are hoping that eventually we'll be able to study the surface of exo planets planets in other solar systems, so we get more data and we could see like, oh, look, there happens to be life only on planets that once had plate tectonics. Maybe there's a connection there. We don't know, but it's something we might figure out in the future if we can see and study other planets.
Mmm. But I guess there's no mechanism for how it might help life that we know about. Or maybe being in a super continent helps or I don't know. Do we have any ideas how that might affect the formation of life.
The formation of life, the actual genesis of life from non living materials. No, I don't think the continents can really play a role, but it might help develop more complex life. It might give life an opportunity to develop in weird new directions. Maybe it's crucial for civilization and intelligence. Who knows, we're really just speculating, hmm.
I see, just arguing about what counts as a continent or not. Using might have the driven evolution for us to be better.
Arguer probably started a bunch of wars. You know, wars have definitely been fought over dumber stuff than that.
Wars and podcasts episodes.
Wars on podcast episodes.
Crucial on the way to enlightenment. As a speak, well, you.
Know, the culmination of all of evolution of life on Earth is this podcast?
So yes, absolutely, yeah, of course we're here to explain the universe. I mean, how much more evolved can it get?
Before we explain the universe, we got to explain the Earth. You know, it's fascinating into me how much we still don't understand and how recent any of this understanding is. As of just one hundred years ago, nobody believed this continental drift theory, and now it's an essential part of modern geology and geography and biology. It's like the theory of evolution. You know, once you see it, you can't unsee it. It's just so obvious. But it takes a while to absorb these crazy new ideas. But those are the best moments in science, right when we have to pivot to something totally bonkers, a new because that's just the way the data is.
Yeah, and it sounds like there are still a lot of mysteries left to answer about how the Earth moves around and what it's doing under the surface, which means that we may be wrong right now. And who knows what we're going to discover about.
The future exactly, not just the future, but also the past. They've done these reconstructions of these super continents from two billion years ago, one of them is called Nuna, and another super continent from a billion years ago called Rhodinia. But that whole history could also be wrong. We may need to rewrite the entire history of life and continents on Earth. It's going to be fascinating to see what people figure out.
Yeah, maybe the continents just looked like a giant smiley face before, and the Earth was hoping that it would freeze with smiling. But then, you know, the universe took too long to take the picture.
Like a giant continent until selfie.
All right, Well again an interesting dive into our own planet, this thing we're all standing on, and how it's moving underneath our feet, and how there are still deep mysteries as deep as the center of the Earth going on right under us, and how long it can.
Take to figure out the story of our very own planet.
We hope you enjoyed that. Thanks for joining us, See you next night.
Thanks for listening, and remember that. Daniel and Jorge Explain the Universe is a production of iHeartRadio. For more podcasts from iHeartRadio, visit the iHeartRadio app, Apple Podcasts, or wherever you listen to your favorite shows. When you pop a piece of cheese into your mouth, you're probably not thinking about the environmental impact. But the people in the dairy industry are. That's why they're working hard every day to find new ways to reduce waste, conserve natural resources, and drive down greenhouse gas emissions. How is us dairy tackling greenhouse gases? Many farms use anaerobic digestors to turn the methane from manure into renewable energy that can power farms, towns, and electric cars. Visit us dairy dot COM's last stainability to learn more.
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