The ground moving beneath our feet
The Earth under your feet has gone through some pretty massive movements over its time, and it will continue to do so, as Adam has been hearing from University of Lisbon's Hannah Sophia Davies…
Adam - The earth under our feet is not as solid or as static as we might imagine. The top layer of the earth, the crust is cracked into pieces called plates, and those plates are floating around on top of the layer underneath, which is the mantle. And as old plate sinks back into the mantle new plate is made elsewhere because the earth isn't shrinking. But how does that all work? I spoke to Hannah Sophia Davis from the university of Lisbon about how the earth moves and what the future might be.
Hannah - There's plates being made and destroyed. So where the ocean is being made is at a mid-ocean Ridge. The big mountain range you see in the Atlantic, on maps of the Atlantic, that's where plate is being produced. And then where plate is destroyed, is in the subduction zone. So you see that in the Pacific ring of fire, this big ring of subduction zones where ocean plate sinks back into the earth and destroys it. As the plate sinks into the mantle, it pulls plates along with it. And so essentially the continents float around and they're being pulled and pushed by the ocean plate as it's being made and destroyed. And that's essentially how the plates move.
Adam - But if everything is always moving about, what did things look like hundreds of millions of years ago?
Hannah - The earth used to be in a supercontinent state. And it tends to cycle between super continents and disperse continents. And that's because oceans are always pushing and pulling as the subduction zones are destroying and ridges are creating ocean. And this has happened several times in Earth's history. Pangea formed around 300 million years ago and broke up around 180 million years ago. And when it broke up, it actually formed the Atlantic ocean. And so that's why you can see that kind of jigsaw fit between the Americas and Africa and Europe, because that's still the remnant of the Pangea. You can see where Pangea used to be.
Adam - We used to have one big continent then with everything smooshed together called Pangea. But what does the future hold?
Hannah - Most geologists will tell you the Pacific is due to close and the Atlantic is due to continue opening. It has this very large mid-ocean ridge that is still producing a lot of ocean plate. Logically the whole thing should kind of turn inside out and Pangea should reform over the Pacific ocean. And this new supercontinent is Non Pangea. So a new Pangea.
Adam - That is basically what will happen if everything continues along business as usual for a few hundred million years. There are other options though.
Hannah - Obviously the Atlantic doesn't have to continue opening, and there is evidence that it might not. This could mean that subduction zones start spreading around the edge of the Atlantic. And eventually we have an Atlantic ring of fire that will end up closing the Atlantic too. And so Pangea could end up coming back together. In that situation, we'd just have another Pangea.
Adam - Could it get even stranger? What happened if the Atlantic and the Pacific both closed up?
Hannah - Ocean plate starts to get more dense as it ages. So it really should start sinking into the mantle after around 180 million years. The Atlantic is currently getting to that age and the Pacific is long past that age. We can envisage a scenario where both oceans close, but if you think about the surf, sorry, the earth, obviously you have to retain that surface area. So a new ocean has to form. And the theory is that there is a rift in Asia, which will split to form a new ocean. And that's the Orica scenario. So essentially the Atlantic and the Pacific both close, and we just have a completely new supercontinent, which looks nothing like any of the other supercontinents and a completely new ocean, which is from the breakup of Asia.
Adam - There is one last idea. If you look at a globe, you might notice how compact everything is up around the North pole and how small the Arctic ocean is.
Hannah - There is a theory that supercontinents like to form 90 degrees away from the next supercontinent because Pangea existed for a long time. And it was a very large continental mass. And essentially it kind of left a bit of a scar in the mantle. As super continents - when they form - geophysicists think that the scar will affect where the supercontinent forms. So the fourth scenario that we have kind of out there to propose what the next supercontinent will look like is the Amasia scenario. And that's essentially just that all of the continents will just kind of smush together in the Northern hemisphere.