Want to travel the world but you don’t have a lot of money? No problem, your continent is drifting across the surface of the Earth right now. In a few million years, you’ll reach your destination.
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Fraser: Astronomy Cast Episode 441: Continental Drift
Welcome to Astronomy Cast, our weekly facts-based journey through the cosmos, where we help you understand not only what we know but how we know what we know.
My name is Fraser Cain. I’m the publisher of Universe Today and with me is Dr. Pamela Gay, the director of Technology and Citizen Science at the Astronomical Society of the Pacific and the director of CosmoQuest.
Hey, Pamela. How are you doin’?
Pamela: I’m doin’ well. How are you doin’, Fraser?
I want to remind everybody, I put in a little ad into Astronomy Cast but, for those who are listening, we are – Dr. Paul Matt Sutter and I – are going to Iceland in February, 2018, to take pictures of Auroras for a week and you should join us.
So, if you have ever wanted to put that on your bucket list and take pictures, or hang out with me and Dr. Paul Matt Sutter, this is what you want to do: You want to go to astrotouring.com and sign up. You can register until August – and you can even cancel if plans change and you decide that Iceland is very cold and you don’t want to be there in February. I understand.
But anyway, that’s just a thing that’s happening and you should totally join us. And if you, you know – you can’t join us for the eclipse trip. So, that’s another thing.
Pamela: Because Iceland’s easier than St. Louis.
Fraser: Yeah, exactly. Yeah, yeah, yeah.
But we want to do a couple of these kinds of things every year, I think. They’re so much fun.
And have you got anything in the shameless, self-promotion department this week?
Pamela: Not this week, nope.
Fraser: Okay. CosmoQuest is awesome.
Pamela: Go do science.
Fraser: Go do science. Here we go.
So you want to travel the world but you don’t have a lot of money? No problem. Your continent is drifting across the surface of the Earth right now. In a few million years, you’ll reach a destination.
So, today we’re going to talk about continental drift. Well, actually, this is Part 5 of our Destroy and Rebuild series. So now we’re going to talk about how the Earth rebuilds and destroys – at the same time?
Pamela: It’s kind of doin’ all the things. It’s one of these things that – It always mystified me, growing up, that we don’t have, like, a rock we can pick up and say, “This rock is 4 billion years old.” There’s some pretty old rock on Earth but, for the most part, any given chunk o’ planet is probably only a few hundred million years old. And that’s weird for an object that’s 5 billion years old.
Fraser: You would expect the world to be able to have rocks from the world. So this is obviously a mystery that has, you know, puzzled geologists for a long time. How did they start to figure what was going on?
Pamela: Well, the way they figured it out was actually a weatherman pretty much looking at the map and going, “Ya know, South America and Africa look like they should fit together.”
And he started looking –
Fraser: And nobody noticed that?
Pamela: Well, I don’t know.
Pamela: I don’t know.
Fraser: This is the story, anyway. Yeah.
Pamela: This is the story.
But he was the first one that I’ve found documented, that went beyond going, “Those two things can fit together” and going, “There’s these weird fossils on both sides –
Pamela: – of where they match.”
There’s these rock formations on both sides of where they match and, in fact, there’s certain critters – like remains of a freshwater Mesosaurus, which is a kind of reptile that looks to me like a crocodile –
Fraser: Mm-hmm. We have them here.
Pamela: That – yeah.
Fraser: Well, we had them here. So we actually have Mesosaur fossils that are found in the local river here.
Pamela: And there’s a band of them that goes from this – what is now the southern tip of South America – to, essentially, Cape Town, South Africa.
And then there is a kind of fern that basically snakes its way from South America, through Africa, up through India, across Antarctica – we find plant fossils in Antarctica – and then –
Fraser: Of course we do.
Pamela: – all the way over to Australia and, if you trace out the fossils and where they match, and you trace out the mineralogy and where it matches, it’s like the puzzle pieces fit together and there’s an even cooler underlying picture with the fossils and everything else.
Fraser: So, we’ve got this situation where the puzzle pieces of planet Earth fit together. And you’ve got items on one side of the puzzle – on the east coast of South America – that match up with the items on the west coast of Africa, just hammering home the evidence.
But this is a fairly new theory, right? I mean, when was this developed?
Pamela: This came out in 1912; it was Alfred Wegener who figured it out.
And the thing was, this was that point in time where we were still figuring out, like – How does the sun work? We were still figuring out –
Fraser: Yeah – What’s a galaxy?
Pamela: Exactly. There were a lot of these now-fundamental questions that we just couldn’t make sense of yet. And looking at this, what I find absolutely amazing in retrospect is people grabbed on to the idea that continental drift makes sense before we even knew what drove continental drift, because the puzzle pieces fit together so well and it just seemed to make sense.
Fraser: That’s really cool. And now, sort of the more modern thinking, the more modern understanding – what is going on? How is this continental – What is the mechanism for this continental drift?
Pamela: So, the mechanism we only sorta, kinda understand. And that’s the cool part is this is one of those theories that we’re like: Okay, this clearly is what’s going on. We now have well-mapped earthquakes. We know this is a thing.
But we’re still figuring it out. We know the energy that drives the continents moving is the energy of the Earth cooling off; so it’s driven by heat energy. It’s motivated, in part, by the convection of basically molten earth inside of our planet and this convective slow boil causes the floating continents to slowly bump and grind and duck under one another.
Fraser: I love that idea, right? That you’ve got this sort of lava lamp with like a waxy crust on top of it and the bubbles of convective cells, of – you know, in the lava lamp’s case, of – you know, it’s whatever is the stuff: the oil and the wax. And stuff that’s inside of it are sort of causing the crust to float around, the continents to float about, back and forth, as the – just as the forces churn underneath on the Earth. It’s a really cool idea.
Pamela: It’s a super-cool idea and what’s really neat about the way it works is we have new crust getting formed. And it turns out that it’s just a little bit less dense than the older stuff that’s been around and gotten squished and has increased in density over time.
And so we find that also gravity helps drive continental drift, where you have places where the much older continents are starting to subduct underneath younger bits of land.
And so you have essentially three different processes going on. You have areas with subduction – which is, again, the one piece going under another. You have areas where the plates are diverging apart from one another; we have this in the middle of the Atlantic Ocean. And then you have what are called transform boundaries. These are the boundaries where continents are essentially rubbing up against each other as they pass not-so-gracefully past one another.
Fraser: And so, where are things going? Like, here in North America – on the west coast of North America – I’m, you know – I’m actually on Vancouver Island. I believe I’ve got my own separate plate. I’m on a different plate from what’s going on over on the mainland but – Where is everybody going?
Pamela: So, different – There are the main plates and then there’s crackty bits –
Fraser: Right, yeah.
Pamela: – of the different things that are doing different things.
So, your area of the continent is trying really hard to head towards Japan. You’re making a break straight west; whether you should or not, that’s what you’re doing.
Fraser: I’ve always wanted to go to Japan.
Pamela: Yeah, it’s a beautiful country. I highly recommend it. You’re doin’ it the slow way.
Fraser: I’m – right. That’s fine. I’m cheap.
Pamela: And then you have California, which is doing its best to head straight North and you have different bits moving in different directions.
The African continent is gradually moving north and east as it’s essentially crushing into the Arabian Peninsula. You have Europe moving north and east as well. You have all sorts of different movements which are essentially leading to the Pacific Ocean area; the plate underneath the Pacific Ocean crashing into Japan and Australian areas.
Fraser: And we’ve got some other dramatic examples, right? We’ve got things like India, which is smashing into Asia so hard that it’s causing all of the mountain ranges there. You’ve got the Great Rift Valley in Africa, which is like cracking open. You can see where the Earth is tearing itself apart and one continent – part of the continent’s going one way and the other part of the continent’s going another way.
Like, once this discovery was made, I’m – You know, the geologists – I wonder how hard they fought it, right? Or did the geologists go, “Okay. Yes, this is it. This explains it!”
Pamela: It wasn’t instantaneous. Nothing in science is except for maybe the discovery of dark energy.
There was tens of years lag between Wegener coming forward and saying, “And have you guys noticed?” And people going, “Yeah, that is indeed what we’re seeing.”
And what it took to make the change was plotting out the earthquakes, realizing earthquakes tend to follow these boundaries and tracing out all the boundaries; and how Wegener had worked to put things together and realizing, yeah. It’s the fossils, it’s the minerals, it’s the earthquakes; all of this painting a single picture.
Fraser: Well, so let’s run the clock in two directions here. We can run the clock forward, of course, and we can run the clock backward.
Let’s start with backward because I think this is one that people are most familiar with. What did the continents look like in the past? Because we are the result, after millions and billions of years, of continental drift. So what did it look like in the past?
Pamela: Well, I think the thing that people are most familiar with is, about 300 million years ago, many but not all of the land masses were unified into this Pangaea land mass; this land mass where we saw North America, South America, Asia, Africa, all fitting together along with Antarctica into one giant piece. And this is where that fossil and mineral record that we were just talking about comes from. But there were still a few pieces that were off doin’ their own thing; Siberia and what became the Baltic nations were hangin’ out on another part of the planet. So we had the bulk of the land mass going down towards the South Pole but there were a few other pieces.
And what always has amazed me is we stop at Pangaea, in when we talk about the plates. History doesn’t stop there. That was just a moment in time when all of what are today’s continents were combined into one land mass. Earlier in history, there had been different land masses. There had been different points of everything merging together. And as we keep winding back the clock, we find different points with different sets of continents.
So, 490 million years ago, there was the single continent of Gondwana; that was one of the things that some things go back to.
Pamela: But it was built out of even earlier stages that broke apart and, in the future, we could end up with great supercontinents yet again.
Fraser: I kind of imagine, right – like, all of these continents floating around and they sort of smash up in one area, and then they go the other way around and then smash up in another part. You would sort of imagine that, right? If you could imagine sort of this floating chunks of wax on the surface of that, once they’d piled up to a certain point, they would then flow back.
But there are parts – I mean, are there any parts of the Earth that are left over from the initial formation or has everything been recycled to this point?
Pamela: We keep finding new oldest rocks. There’s been a few found in Canada. There’s been a few found in Africa. But there’s no one part of the planet that you can point at and say, “And this section of the planet is extraordinarily old.” There are just small sections that have rogue rocks, essentially.
Fraser: Right. But still, like, we can’t – Like, if we didn’t have an independent way of knowing the age of the Earth – thanks to the meteorites – we would really have no way to know how old the Earth truly is, because there is no rock that is older than some of the stuff that’s formed just, you know, within a billion years after the formation of the Earth. We just don’t know.
Pamela: And – Well, we keep coming across things that help us get there. So we will find fossils from different periods and it was – In fact, yesterday was the anniversary of the discovery of Carbon 14, which gets used to do a lot of radioisotope dating. And we can go back more than 300 million years with the fossil record. It’s just, how do you date a rock that isn’t embedded in fossils? This is where it gets messy.
And so, trying to figure out – Well, okay. So maybe you have this rock over here that has this set of isotopes that it can get used for aging. It’s – This is where it gets hard unless you’re relying on the radioisotopes within fossils.
Fraser: Right. I mean, they have, like, uranium and they have other elements that can be used to look for – they have longer half?lifes that can be used to look further back.
So this is, of course, Astronomy Cast. And so let’s take this concept of continental drift and look elsewhere, both in our solar system and really in the universe.
Is there any other place in the solar system that has continental drift?
Pamela: Not like we’re used to here on Earth, where we have our set of fairly well-defined continental plates and small plate tectonic events; like your part of Canada trying to head towards Japan.
Fraser: Yeah. See ya later.
Pamela: We’d thought for a long time that Mars didn’t have any plates but some new papers are starting to hint that maybe it has two plates that are just sort of going back and forth, like two things floating on top of a boiling kettle.
What’s cool, though, is Venus seems to have avoided the whole plate tectonics thing altogether and, instead of having these plates – like wax – moving back and forth and diverging and going under one another, it seems to simply have flipped its whole surface now and then. There are hints that instead –
Fraser: Like, it just – It just, like, turned itself inside out.
Pamela: Yeah. “I’m done. I’m just gonna –
Pamela: – give off a whole bunch of heat right now, have massive volcanic eruptions and resurface my entire world all at once.”
Pamela: Yeah. So, there’s different models. And one of the things that I’m really hoping to get to see over time is, for instance: How do you handle something like Io, that’s constantly resurfacing itself? Can we – if we watch it long enough – start to see some of these longer lasting volcanoes –
Fraser: Right, right.
Pamela: – moving relative to one another?
Fraser: I mean, you would think that –
Pamela: So, will we find plates there?
Fraser: I mean, you would think that Io would be a classic candidate for this kind of a thing; that it’s clearly got so much volcanic activity and it’s got these active volcanoes, how long have these things been running? What is going on there?
But here on Earth, I mean, we have really sensitive laser rangefinders that are used to measure distances. We don’t have such a thing on Io.
NASA, take a note: We need some kind of plate tectonic instrument package to be landed on the surface of Io.
Pamela: And then, looking at worlds like Europa – with its ice that is constantly moving – we see the cracks, we see the tears. And do you have masses that, in some ways, act like plates over the ocean waters?
Here, you have a different gravity, you have a different way of thinking about it, but we’re still working to understand the underlying physics in plate tectonics and continental drift. So, can we someday treat some of the ice masses the way we treat land masses here on Earth?
Fraser: Yeah. I mean, the surface of Europa clearly looks like there’s some kind of process that’s going on. You’ve got these amazing cracks and, like, scars and scrapes, but also regions that are very smooth. Like, you don’t see a lot of craters on the surface of Europa and so you know that it’s being resurfaced somehow.
And so, just imagine – This is even a much better analogy, right? Because you’ve really got – You’ve got boiling water. You’ve got frothing, boiling water in Europa because of the tidal forces and then you’ve got this ice on the surface – the shell – that is in contact with space. And so, it’s cold and constantly refreezing and then this – you know, cracks opening up and water welling up and then other areas subducting underneath. Things like that.
But even this idea of cryotectonicism is kind of, you know – It’s thought that this is everywhere, right? But it’s not just Europa, but maybe we’re seeing this on Enceladus; we’re seeing this on Ganymede; we may be seeing this on Pluto. Right? Like, this is perhaps one of the dominant factors that’s going on with these worlds.
Pamela: And it all comes down to: Is the surface being remodeled through a process driven by the energy of heat trapped in the world from its formation and from its tidal events? And is it convective processes and gravitational driving forces that are causing this motion that we’re seeing?
Fraser: Yeah. I mean, just to look at Pluto, for example. I mean, there’s these amazing plains of just very smooth ammonias and ices and methane and things like that. And then you’ve got these mountains of, like, water-ice. And so you can just kind of imagine the same processes that are happening here on Earth, but where it’s rock, are there happening and it’s water, which is – It just – It blows your mind.
So, let’s talk about – Like, let’s go further then. So imagine crazy alien versions of this; places that are tidally locked. Like, we just – you know, we discovered – This new announcement of the TRAPPIST?1 planets; they’re tidally locked, they orbit their planet within a day – 1.4 days is the closest one, out to 20 days at the furthest one. Could we be seeing some kind of continental drift, tidal act – you know, tidal forces – on those sorts of planets?
Pamela: It’s – There are so many different scenarios that you have to worry about: What’s tidal-locked to what, what sorts of synchronicities are there?
To go to a much simpler case – where we’re only looking at two bodies rather than eight with a star and seven worlds – if you have two fairly similar-sized planets that are tidally locked to one another, you can imagine that, over time, the continents will all slowly drift so that one set of land masses is constantly facing the other set of land masses. And that would be disconcerting because, I mean, think about it. The one world has the potential to constantly eclipse the other and vice versa, depending on their size and distance ration, and their sun size and distance ratio.
Imagine if you were cursed, basically – always be eclipsing your star with your other planet’s cities straight overhead.
Pamela: So, the tidal locking could influence how the continents drift and then lock them into a place where they’re just locked facing the other world.
Fraser” What does the future hold for the Earth? Are we going to go on, continental drifting forever? What would stop it? Are we going to become like Mars? What does the future hold?
Pamela: We will eventually cool off. It’s one of those “in the fullness of time” things, where people – It’s every few years, you see a new calculation for: Will the sun consume the Earth or not? And you see a new calculation for: How long is it going to take for the Earth to completely cool off and lose its magnetic field?
In the fullness of time – given we’re not eaten by the sun – the Earth will cool off and the continents will stop drifting. But until then, our world is constantly building new oceans; it’s building new land masses.
What drove me to suggest this show was the realization that New Zealand – which is one of the youngest bodies of land on our world – it doesn’t even have, like, indigenous mammals really, because birds could fly there and, well, not so much for things that weren’t birds.
Pamela: And it’s so young that it hasn’t had big animals get there through other means. There was no bridge, like we had –
Pamela: – from Asia to the Americas. So, this young piece of land, rising up out of the ocean, it’s being realized it’s a new continent and will grow and expand over time and over earthquakes and – Build safely down there, folks.
Fraser: Yeah. That announcement was made just in the last couple of weeks, right? That New Zealand is now brand-new baby, actual continent Zealandia?
Pamela: Yeah, Zealandia.
Fraser: Yeah, congrats everyone in New Zealand. You’re members of the continent club; very auspicious.
Well, thanks Pamela. We’ll talk to you next week.
Pamela: My pleasure.
Male Speaker: Thank you for listening to Astronomy Cast, a non-profit resource provided by Astrosphere New Media Association, Fraser Cain and Dr. Pamela Gay. You can find show notes and transcripts for every episode at astronomycast.com. You can email us at email@example.com. Tweet us @astronomycast. Like us on Facebook or circle us on Google Plus.
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Duration: 27 minutes