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Current time:0:00Total duration:6:02

Video transcript

what I want to do in this video is talk a little bit about maybe why the plates are actually moving in the first place and nothing I'm talking about this video has been definitively proved this is just kind of the current thinking the leading thinking on why plates are actually moving although we haven't seen the definitive evidence yet and it's probably a combination of a bunch of things now before we even talk about plates let's just talk about convection and you might already be familiar with the term but just in case you're not let's do a little bit of review of convection so let's say I have a pot over here so that is my pot and it contains some water so I have water in my pot and I let's say I only heat one end of the pot so I put a flame right over at that end of the pot so what's going to happen well the water the water that's right over the flame is going to be warmed up that more than any of the other water so this water is going to get is going to get warm but when it gets warm it also becomes less dense when you have a fluid if you warm it up you're going to the molecules are vibrating more they have more kinetic energy they're going to bounce further distances away from each other they will become less dense and if you have something that's less dense and it's surrounded by things that are more dense and we're dealing in kind of a fluid state right here that warm less dense water is going to move upwards is going to move upwards well when it moves upwards something has to replace it something has to replace it so you're going to have cooler water cooler water from this side of the container kind of replacing where that water was now this water as it rises as this water rises what's going to happen to it what's going to cool down it's going to get further from the flame it's going to mix with maybe some of the other water or some of the other water or transfer some of it's a kinetic energy to the neighboring water so it'll cool down but once it cools down what's it we're going to want to do remember in general the closer you are to the flame so the water closer to the flame in general is going to be warmer so all of this stuff is going to be warmer and all of this stuff up here like the coldest water is always going to be farthest from the flame and so it's going to be the coldest water is going to be over here but remember the coldest water is also the densest water so the dense so this water over here is dense and so it will sink it's denser than the water around it and it also helps replace the water that's going here to get warmed up again and so what you do is you have the cycle here warm water rises moves over to the right down here and then goes back down as it cools down and it's dense and then it gets warmed up again and so this process and this process essentially what it's doing is it's it's transferring the heat it's allowing the heat to be transferred from this one spot throughout the fluid and so we call this process this as this is convection this is convection now the reason why we think the plates are moving is because we think that there are similar types of convection cards in the asthenosphere in the mantle in the more in the more fluid part of the man to remember the mantle most of the mantle is kind of this you can kind of view this mushy spongy not quite liquid but not quite solid state kind of plastic it can kind of kind of mush past it can kind of flow like super super super thick you know I guess you could call them you know like well like super viscous fluid so not quite solid not quite liquid but the same thing could be happening you have certain areas in the mantle that are hotter than others in this particular in the asthenosphere and those areas that's where you're going to have that's where you're going to have the material in the mantle move up because it's hotter it's less dense and it will move up and maybe it'll cause one of these divergent rifts where content where where kind of plate material and crustal material is forming and then as it moves up it cools down it cools down it cools down and eventually sinks and eventually sinks only to get heated up again so it has these kind of circular motion just like we saw with the boiling water and so that process remember this isn't this isn't completely liquid so it is rocky so it's going to it's going to potentially be able to take other things with it it could maybe drag the crust along with it and that would cause that or I should say it could drag the lithosphere along with it not just the crust it could drag all this rigid rock up here along with it causing it to move causing it to move in that general direction so you have the drag there you could also imagine that just kind of a suction effect where if you view it as a fluid you have a bunch of fluid coming down here so it kind of pull the lithosphere down at those points and would kind of push the lithosphere up it would push the lid the sphere up at those points so you have these convection currents you have these convection currents that are essentially that are essentially driving and you know these aren't going to be super fast moving fluid convection currents like you would expect with boiling water or with heated water these would be slow-moving convection currents but they're moving they're moving enough and they're able to kind of put enough drag on the lithosphere to take the lithosphere along with it and so that's kind of at a high level the dominant theory as to why they're moving there's other ones that talk about you know maybe these these these the lithospheric plates there's their cut they're kind of they thicken as they move further away from this these this area where the ridge is forming and if we look at this oceanic crust right over here and so over time there's kind of their denser over here because there's more there's more cooldown material at these points and so and that's it's already a little bit lower because this is where a lot of the land is being created and so there's maybe some gravitational effects but the dominant effect we think is due to this convection in the upper mantle