hello geographers welcome back we are talking about what's inside the earth so in our last lecture we talked about geologic time and how we break down the earth's history and how we know what we know about the earth's history now we're going to take a look inside the earth and as we look inside the earth we're going to break down the inside of the earth by chemical composition and by basically if it's solid or if it's liquid and something that's interesting about inside the earth is that we know not so much about inside the earth so we know more about the universe than we know about what's going on inside the earth we know more about what's happening way out there than we know about what's happening right in here isn't that life you all isn't that just uh what life is where we know everybody else's business but uh when it comes to us we just don't quite know what's going on it's that and it's also that it's really hard to get in here analogy works both ways um it's hard to get in here it is dense and it is hot so we don't know that much about what's going on inside the earth what we know about what's going on inside the earth is what's happening right up here on the surface so in the asthenosphere and the lithosphere that word i keep saying so the lithosphere also called the rock sphere that's what's right underneath us so we know about the part of the inside of the earth that affects us most once again analogy works again and again that we know more about what affects us than what else is going on in the world okay i'll stop with that analogy all right so i have a well actually i won't stop without analogy because i even did a quote for it open your eyes and look within are you satisfied with the life you're living okay so let's look at the earth let's look at plate tectonics black plate tectonics let's look at the three different types of plate boundaries there's three different types but one of them has like a column a and a column b and uh yeah so here's our earth once again we know this isn't the earth because remember the earth is thicker in the middle uh but for the purpose of this diagram we'll have this nice perfect sphere right here and inside we have the core so we have the core so first i'm going to go through the chemical composition and then i'm going to talk about what state it's in if it's solid or if it's liquid so our core is iron now it's iron because iron is heavier once the further inside the earth you go the more gravitational pull you get so basically what's heaviest is going to get sucked into the middle and then we have the mantle that's iron again heavy and then some magnesium silicates not so heavy and then we have the crust and that's where we're going to see our lightest silicates and the crust is broken up into two different uh layers the asthenosphere and the lithosphere so we could break down the core to the inner core and the outer core because while the core the chemical composition of it is iron the uh um state of it is solid and liquid so the inner core is solid because again the gravitational pull is so intense that like all the iron is just sucked right in we are learning right now that the inner inner core the inner inner core has been hidden away from us but through you know a lot of therapy the earth has discovered that the inner inner core is actually liquid again because it's so hot once you get in there it's just like molten iron just imagine that okay so we have our inner core solid our outer core liquid and then our mantle is broken up into the lower mantle and that's a hard solid in the lower mantle and then we get into the upper mantle and the upper mantle is broken into these two pieces the asthenosphere and the lithosphere and those are very important to us so i like to there's lots of different analogies most of them are food analogies for the asthenosphere and lithosphere but i like to relate it to pie so if the asthenosphere is like a peach pie or like let's say we have a pie let's say we have a peach pie okay so the asthenosphere is like the pie filling you know what i'm talking about like the nice warm uh squishy that's a scientific term squishy um so it's a nice like firm ish but very easy to cut through very easy to kind of fall apart that's the asthenosphere it's like the it's like the filling of a fruit pie it's you know it's dense it's solid but it's a soft solid and then we have the pie crust on top and that pie crust is solid it's hard but it's really thin it's really brittle it's easy to break uh you know it's easy to cut if you like if you kind of like i don't know how you do this but if you like bend your pie um that crust on top is gonna kind of easily like break into itself and you're gonna have little piles of pieces of crust um and if you have like pieces of the crust kind of slide by each other also you're gonna have little crumbs again those are mountains in this whole analogy okay so our stenosphere some people like to relate it to butter like butter um meaning that asthenosphere is like the butter that you leave out on the counter and the lithosphere is like the butter that is in the refrigerator when you're talking about like hardness okay so our lithosphere rigid outer asthenosphere warmer plastic lower mantle solid outer core liquid inner core solid so oops so uh pause this get all of that down make sure you know it and we could relate this to a cookie if you think about the lithosphere as the top of an oreo cookie and the creamy filling as the asthenosphere so once again imagine those consistencies so let's take our different types of plate boundaries now if you imagine again that creamy filling is the asthenosphere and this cookie is the lithosphere and the lithosphere is sliding over the asthenosphere and that's that's happening for a couple of different reasons let me go back here real fast so think about it um think about how this is warm really i'm not warm and this is freaking hot right uh this is really really really hot and so what happens to heat it rises so this heat is gonna rise rise all through the mantle and then when it gets to the buttery peach pie asthenosphere what we're going to see is we're going to see the asthenosphere rise up it's going to hit the crust of the lithosphere when it hits the crust of the lithosphere it's going to make its way over here gravity is going to pull it back down and what do we have what is that so if the heat is rising and the sphere kind of bubbles up and hits the top of the lithosphere and then it grab moves to the side gravity pulls it back down it heats up again it goes up if you said that is a convection cell that's exactly right that's a convection cell so our lithosphere our plates are moving over the lithosphere most likely because of that convection cell there's some new evidence that maybe what's moving our plates is a gravitational pull more than the heat of the lithosphere but that's all very new information just like the inner inner core is new information okay so if our plate if our lithosphere is sliding over the asthenosphere what happens when it breaks because imagine that we have the asthenosphere all over the surface of the earth but it's cracked like an egg and it's moving because of the because of the convection cell and the asthenosphere or maybe because of gravity and so sometimes it's going to crash together sometimes it's going to pull apart sometimes it's going to slide next to itself next to each other whatever okay so our first plate boundary is our divergent plate boundary divergent so they move away from each other um moving away from each other now if you think about this being the lithosphere and this white being the asthenosphere and think about how there is a convection cell in that asthenosphere what's going to happen if you have this divergent boundary the asthenosphere the magma basically what's inside the earth instead of hitting the top of the lithosphere like it normally does and then getting pulled back down and circulating in our convection cell it's going to just keep on going straight up right so you have this divergent plate boundary now there's a break and here comes the magma and instead of hitting the lithosphere it just kind of comes up and just imagine like it oozes out um it is the most when we're talking about mountain building it's the most mellow of mounting building it's the most kind of like uh chill mountain building it is not a vesuvius it is not mount saint helens will mount st helens i think the ant the 50th anniversary of mount st helens was the other day that was this huge strata volcano that erupted in washington state that doesn't happen on a divergent plate boundary divergent plate boundary leads to seafloor spreading it leads to like really gradual gradual building of the earth's surface the convergent plate boundary so the convergent plate boundary is the opposite of the divergent plate boundary in so many different ways so instead of spreading apart they are crashing together they're crashing together and this is gonna be your like mount vesuvius stratovolcano uh mountain building that's to happen on your convergent plate boundary and remember how i said for our three plate boundaries there was one that had like a column a and a column b this one has the a and the b basically so convergent plate boundary when you have two different plates of equal mass so if they have equal mass and they run into each other they're just going to kind of go like that right and so if we have different types of plates we have oceanic plates and we have continental plates around the earth if you have a continental continental plate colliding like we do right here in asia so south asia india is colliding converging into the rest of asia and so those two equal masses are hitting each other and what are they creating right here the himalayas but most of our convergent plate boundaries are oceanic continental so like over here in south america we have the south america plate and we have the nazca plate which is a piece of the piece of basically the pacific ocean out here so the nazca plate and the south america plate are converging into each other and they're converging they're not equal mass so because they're not equal mass the oceanic plate is diving under the continental plate so the oceanic plate the nazca plate is diving under the continental plate and it is creating the andes the andes mountain range with its incredible steep strata volcanoes and its violent eruptions and it's just massive mountains so our um our convergent plate boundary that is not equal mass is a convergent subducting plate boundary and i'm going to have a slide on that that says that out in just a minute but so we have our convergent equal mass and our unequal mass oceanic and continental which leads to a convergent subducting the subduction is the plate is getting pushed under the other plate and that leads to a lot of things it leads through the recycling of the lithosphere especially for example so i'll get into that in just a minute okay our transform plate boundary that's when instead of diverging instead of converging they're just kind of sliding next to each other that's what's happening right here in california so with the north america plate in the pacific plate the pacific parade is making its way up north and the north america plate is making its way on down south and they're basically just sliding by each other but they're not sliding by each other like two ships in the night they're like sliding by each other like a car side swiping another car they're just they're like right and so that builds mountains but it doesn't build the andes mountains it builds like the coastal mountains that we see in california not the um you know seventeen thousand foot mountains but the three thousand foot mountains that we see along here there's a lot of different things happening here in california that's building all of our different mountains we have the sierra nevada mountain range uh sierra nevada mountain range are not old mountains you should be able to tell that just from like the sheer steepness of their slopes um they were created from a convergent subducting plate the fairlawn plate dove under california and completely subducted under california and then the north america plate and the pacific plate have been transforming sliding by each other when they do that they create the coastal mountains but then also you have like baja california that's being pulled with the pacific plate and it's like pushing up into california creating the transverse mountain ranges so don't worry you won't have to remember all of this but this is just some idea of how california is a great example of so many different things and one is all the different types of mountains that can be built the sierra nevada the coastal ranges the transverse ranges there's all different processes that are creating those mountains california also has all three deserts if you remember okay so once again here we go our crust our mantle lithosphere is hard status you're softer lower mantle is hard and here is our cracked egg shell there was the nazca plate i was talking about diving under the south america plates here you've got the cocos plate just a little plate caribbean plate the north american plate the south american plate these two are converging right into each other plus you have the north america plate moving north so it's diverging you have the south america plate transforming just imagine the caribbean and like the massive massive geologic processes that are happening in the caribbean anyway so yeah take a look at this all our different plates notice the african plate um africa is right in the middle of the african plate same thing with australia over here guess who has the least amount of mountains in the world guess it's africa and australia why would they have virtually no mountains because nothing is converging into them all these other continents with their massive mountain ranges the alps the himalayas the uh rockies the sierra nevada the sierra madre's the andes they're all being created because you have these converging plates but these two continents over here that are just like cruising in the middle of a plate they don't have massive mountain building they do have mountains but they're created from a couple different processes okay so if we look at um our matching geology remember south america fit right into africa and then they drifted apart as we do sometimes on north america africa how do we know all of this watch that that video that i posted on pangaea uh we know it from like i said uniformitarianism from volcanic uh data collection we know it from kind of matching rocks if you imagine that there's there's there's going to be different mineral uh and minerals and then rocks and different processes that are very similar to each other on these two different continents in two very different places that's one of the ways that we match together these besides that they look like they fit into each other we can also see data that tells us about mountain belts that were created in one part of earth's history a crust that was created in different parts of earth's history so now looking so we've been looking at the macro right we've been looking at the macro building of mountains now if we look at other geologic change kind of on the micro scale now it's not micro in the same way that we talked about the climate but if you imagine we're talking about big plates and now we're talking about some of the like more localized processes that happen so we have two things that are happening with landforms or two types of landforms or two two significant impacts to landforms those are endogenic and exogenic forces so endogenic forces what's coming inside the earth what the lithosphere is doing how you have um converging plate boundaries but you don't just have things happening to the earth's surface at the plate boundaries there's also going to be all of these other kind of ripple effects remember if we try to take anything from the universe and pull it out we're going to find that it's connected to everything else so let's go over here to north america again north america is hard to see um here's north america and here's california and california like i said has a lot of different california is a great place to study anything almost anything california has all the different types of mountains like i said all the different types of uh of um deserts we have microclimates here because of all of our mountains because of our cold ocean currents because we have valleys because we have high elevation because we have coastal communities it's a great place to study microclimates it is also the most diverse state in the country it is the biggest gdp in the country california has the fifth biggest economy in the world 13th biggest and or no sorry not 13th biggest um but uh fifth biggest in the world although right now that might not be true anyway california is a great place to to um study i teach a whole class on california geography in fall all right so when we're looking at california or sorry when we're looking at this part of north america we once upon a time like i said had a converging plate boundary the farallon plate subducted completely underneath north america and then now we have the north american plate and the south american the pacific plate and the north american plate going in two different directions and i was saying yeah yeah yeah sorry um i don't know if i said this correctly in a previous slide but so the pacific plate is moving up and the north american plate is moving down did i say that i'm not sure i might have like said something that kind of sounded counter to that when i was talking about the mountain building in california earlier anyway um so they are transforming they're sliding next to each other so you have what's happening along the coast and what's happening along the plate boundary the earthquakes and stuff like that but then you also have inland different exogenic and endogenic processes happening so with this transform boundary if you imagine you have a lot of pressure on the plate and so if this is north america if you imagine there's the stuff that's happening right here as a reaction to the plate boundary but then there's also also stuff that also stuff that's kind of stuff that's gonna happen if you think about like the pressure that might be put on a plate if you have the converging plate boundary there's going to be the pressure right here at the boundary but then that's also going to affect the rest of the plate and you can have what's called compression that compression can lead to tectonic uplift so you can have different uh you can have you can have different exogenic and endogenic processes that lead to mountains or plateaus or different topography away from a plate boundary because of something like compression if you imagine that you have this this plate that has the process happening right here at the border of the plate the boundary of the plate but the rest of the plate is being squeezed and when it's squeezed just imagine there's like a and then and you've got like these processes these endogenic processes that are leading to uplift and so that's what that was it was like mountains there's supposed to be like a plateau popping up here comes the colorado plateau he's really um advanced tactics when i'm teaching okay so endogenic processes those are things that are happening inside the earth and they're not just limited to plate boundaries they can also be things like compression or extension so in the same way you could also have a plate boundary that or sorry a plate that's being stretched it's being extended that's happening and guess what california um and you can have rifting you can have entire so in africa over here you have africa once again remember africa is pretty flat but uh there is a significant mountain range that significant mountain range is runs from lebanon where are you so runs from lebanon all the way through this eastern part of africa all the way down to mozambique so it's called the east african rift so this is the east african rift it's also called the albertine rift but uh albert does that sound what does that sound like that sounds like a colonial name right so the east african rift runs all the way through here and it's leading to the mountain like the significant mountains that you would see in africa so when i say africa is pretty flat people might say something like what about mount kilimanjaro okay yeah now kilimanjaro is a significant mountain it's 19 000 feet over here in tanzania um and then mount kenya just north of it is 17 000 feet so there are significant mountains here and they're happening not because of convergence not because of uh subduction they're happening because of rifting basically basically you've got everybody moved away from africa so africa is getting stretched and if you imagine like stretching out a sweater and stretching out that sweater eventually you're gonna see kind of a rip in it that's what's happening with the mantle right there where you have this rip and it's building mountains it's building mountains all through here you have volcanic you have volcanic activity all through here volcanic soils which are extremely rich so you have these rich iron-rich volcanic soils and remember this is right at the tropics so we're going to have a whole lot of water we're going to have a whole lot of the sun's density sun's density sun's energy so what are we going to have right here a whole lot of life because you have this incredible uh iron rich volcanic soil happening because of the geologic processes and then you have the the atmospheric processes up here the climate that is leading to a lot of water a lot of the sun's energy this is the most fertile part of africa right through here this is the most fertile agricultural part of africa it's also going to be the most densely populated part of africa because once again the best soil means that there's more competition for land more competition for agriculture and yeah africa i've said in earlier um lectures people tend to say like oh there's so many people in africa there's not that many people in africa really africa is a gigantic place and in no way is it too populated overpopulated but where we're going to see the densest population is through here still not the most populated countries the most populated country in africa is nigeria one in five africans in nigeria some information for you general trivial information for you so those are endogenic processes things that are happening inside the earth compression extension plate boundaries all that stuff and then there's what's happening outside the earth exogenic so exogenic forces that is weathering that is basically i've said this before the earth is constantly building itself up there's all these processes happening inside the earth that are leading to mountains leading to plateaus leaning to all of these these uh geomorphic processes that are leading to our topography and then the earth breaks itself back down again you have water you have wind you have freezing and heat that are just breaking down the earth like just built these mountains and then weathering comes along and breaks it apart so we're going to talk about weathering later but weathering are the processes that basically like break down rocks so here's the earth building up a mountain and here comes the weathering processes that just tear it back down again and that's what leads to if you have this compression that could lead to like a nice flat plateau like that and then here comes the ice and the rain and the wind and it tears down and creates all the peaks and the valleys and the ravines and the rills and the gollies and all the different parts of what we usually see in a mountain range okay so here's our different plate boundaries once again the asthenosphere so this is what's happening where we have mountain building so with our divergent plate boundary right here two plates are moving apart the asthenosphere makes its way up through the break in those plates remember that's going to happen because of the convection cell then we have our transform plate boundaries that's not necessarily letting out what's inside the earth but it's going to lead to it's going to lead to a accretion that's going to lead to like basically that if you imagine the crust kind of gets gets uh broken apart and piled up that is a very weak way of explaining that but it's it's not going to lead to like significant mountain building new mountains but it could lead to to new uh it's an exogenic process that could lead to new landforms that's what i'm trying to say and then our convergent and remember this is specifically going to be a convergent subducting plate boundary right here where you have two plates smash into each other and then a hot spot now a hot spot is not a plate boundary a hot spot we do not know very much about first of all and a hot spot is where you have a thin part of the mantle a thin part of the lithosphere so a thin part of the lithosphere and a particularly viscous plume of magma making its way through without any kind of break so there's no plate boundary happening in a hot spot there's just this weird kind of anomaly where you have a thin part of the mantle and you have the asthenosphere you have the magma making its way up through that's how hawaii is a set of islands right in the middle of the pacific ocean right in the middle of the pacific plate the pacific plate borders california over here it borders it runs right through japan it goes the pacific plate is gigantic but um the hawaiian islands are right in the middle of it and they are a result of a hot spot they're a result of a plume of magma that's just bursting its way just like making its way up into the lithosphere and it's one of the ways that we so this is the hawaiian islands are one of the ways one of the things we use as evidence for plate tectonic movement because essentially the hawaiian islands the southernmost island hawaii is still being built it's still over that hot spot and each one of these other islands and they continue all the way past the ones that we know so kawaii is usually the kind of people think of as the last island the most northern island but actually continues like all the way up here those islands are once upon a time if you imagine you have the hot spot and the pacific plate right here and the pacific plate is moving over the hot spot and so as it moves over you got an island and then you got another one that comes up and then that makes sense and it keeps going so you have the hawaiian island chain here's our subduction zone all spread out for you it's a pun um so this is also the seduction zone is really important because it builds like significant mountains like the andes for example but it also recycles lithosphere and i said that earlier let me just explain what that means so imagine we have like solid rock we have solid rock and rock is two or more minerals so rock is a basically a composition of chemicals and that those that rock that solid rock that solid part of the crust gets pushed in the subduction zone under under the continental plate and down into the asthenosphere and what's the asthenosphere like it's like pie right it's like melted butter um so melted butter so once it gets down here the rock melts back down and becomes this part of the asthenosphere again and new magma new rock gets pushed up with the convergent plate boundary and when it gets pushed up you have this new magma that pushes up through the crust and so now you have new rock and old rock has been recycled so that's what i mean by this is the earth is constantly recycling everything the earth doesn't waste anything it recycles water it recycles rock it recycles life it recycles carbon everything just gets like goes around and around and around okay so i'm going to see you next time when i talk about rocks okay rocks you