into our first lecture which is the um discovering the layers of the earth um i've heard many different analogies for what the earth is like so one example is i've heard that the earth is kind of like a jawbreaker what i mean by that is that it has different layers that have different um characteristics and at least when i was a kid when i would have a drawbreaker in my mouth flavors would change the colors would change i've heard the earth is like an onion i don't like that analogy as well because each layer is different has a different composition it has different properties whereas onions are going to be the same as you go with throughout another um analogy that i've heard that's pretty good is it's kind of like a peanut or like one of those crispy m ms um because you have like the outer candy shell which is like our crust and you have the chocolate which is like the mantle and then you have the inner center um the only problem with that is that the cru the inner center of the earth actually has two different properties um so if we're thinking about the earth as like a jaw breaker each layer has its own characteristics the only part of the earth that we've actually been able to interact with is the crust we've never actually been able to directly contact the mantle the liquid outer core or the solid intercourse but as we're going to learn in this portion of the lecture there are several different ways that we can um investigate that um but you can see here the crust is that very thin which is why kind of like the m m analogy is that very thin outer crust then we have the mantle which is actually the largest volume and we have a liquid outer core and a solid inner core many of you have probably seen a map that looks something like this um this map has the cottons in it which are either have green or that kind of brown can color um some have ice like on the himalayas and um antarctica and greenland um darker brown as the mountain areas lighter browns the desert areas and then we have the blue parts which are water so the earth is divided into continental crust and oceanic bases um the differences in competition in the in the composition um do heavily impact how the earth changes through time so the crust um this is the earth's surface the portion of the earth that we have access to and that we're familiar with um most of the surface is dominated by either water land and percentage-wise there's actually more ocean than there is land water is part of what we call the hydrosphere this includes groundwater ice and surface water surface water can be lakes rivers um or ocean um land is part of the lithosphere and the crust of the outer shell so we have oceanic crust and continental crust these have distinctly different properties that we're going to learn about more later this portion of the lecture now i want you to see what the percentages are um for these um i would never ask you to know that the earth is 35 iron i might ask a question like what are the four major elements iron oxygen silicon and magnesium you wouldn't have to list them in order you wouldn't have to give me the percentages but just know that most of the earth if we're looking at the earth as a whole is iron oxygen magnesium and silicon um so and then the rest of the 88 naturally occurring elements are about 10 of the earth's composition we're going to see when we break down the earth's crust versus the earth's mantle that these iron oxygen silicon and magnesium are going to keep coming up but the percentages may differ depending on where you are on the earth so what is the earth made of this may be something that you've thought of before or something that you've never really thought of before it might have just been something that never occurred to you as what the earth is made out of um so the elements that combine to make the earth um there's minerals on the earth these are inorganic meaning that they are not made by an organism um solid um they're crystalline which means that they do not flow have a set structure to them so think of them as kind of like being um tinker toys put together instead of slime and they combine to make rocks therefore most of the earth in contrast to these crystalline violence there are glasses which are non-crystalline which means that they don't have a set so think of slime if you've ever been in an old um building and tried to look out the window and you look at when out the window at different angles and you see that kind of waviness um what's actually happening is glass is what we call an amorphous solid what that means is it naturally flows so that's why when you're in an old building um the house i grew up in was is a little bit over 100 years old so um and our windows are original so when i'm sitting in the living room in the house that i grew up in if i look out at certain angles i see that the window is not flat i could see this kind of movement through time well there's natural glasses on earth too some of you have may have heard of obsidian obsidian is a gemstone for some it's used a lot in glory specifically like um like um snowflake obsidian um obsidian was used in arrowheads historically tools and it used to be used as scalpels too um because it has a little scarring because of its ability to get very sharp um rocks are there's three main types of rocks on the planet only three categories and then the rocks are sub-categorized within those major categories of those three categories we have igneous rocks means we're going to think volcanoes these are cooled from liquid we have metamorphic rocks these are formed from heat and pressure and we have sedimentary rocks these are basically the recycled rocks these are rocks that are formed from um some type of weathering if it's physical weathering it can actually be broken into smaller pieces and then glued back together if it's chemical weathering they can be actually dissolved and then re-precipitated so think about like the white footprints that we get along we get everywhere in the wintertime where that salt has been dissolved in our boots our shoes tracked in on a floor and then evaporated to leave behind the salt crystals um the earth also has natural organic components that contain carbon um these are mostly evidence and left behind by formerly um living creatures so we're thinking wood we're thinking coal we're thinking oil these are geologically rare think about if you cut an avocado or if you cut an apple and put it out on the counter if you don't put lemon juice on it or for the avocado if you're making avocado or guacamole for like a party you don't put it back in it it's gonna turn brown pretty quickly that's because oxygen is reacting with those organic materials in that food so that's why we don't have a lot of preserved wood coal and oil because oxygen will readily decompose these materials the earths are made of metals these are solid and these are made out of metallic elements in this class yes we will be handling chemistry particularly when we start to talk about rocks and minerals but i'm going to try to make it as basic as i can um there might be parts where i go a little bit more than i might want you to know on a test but i i'm adding that information because i think it might help you understand a concept later on um i understand some students might be a little bit hesitant with chemistry that could be a scary topic um don't again i'm going to go back to that idea don't hesitate to reach out to me just because i explain things in one way in this video does not mean that i can't explain it a different way so please if you're starting to feel a little bit lost or overwhelmed put those questions in your discussion board maybe your classmate has a way of looking at it that can be helpful to you if um and again when we're doing the discussion boards don't hesitate to reach out if your classmates have an answer and your question and you think you have an answer type it out if you're not quite right that's okay it's better to learn that you're not quite right and have it have me say well good job thank you for trying but let's just look at it from this perspective um i'm here to help you learn and we learn by making mistakes let's be honest um i'm challenging you to kind of go to that place that you might not be comfortable and i know that's uncle i know that's well that's uncomfortable but i know that that's not a pleasant feeling um but by going there and by kind of expanding and sitting there for a little bit um that's how we grow and learn and i'm not here to criticize you so just kind of keep that in mind i'm here to help you so if you do go out at a limb and you happen to make a mistake that's okay it's better that i catch it and i and you make that mental note now then you make that mistake on a test um we also have melts or liquid rock um in the crust that's where those that's why we have volcanic eruptions um so these are rocks that have actually been melted um into a liquid um if it's beneath the surface we call it magma if it's on the surface we call it lava and when we talk about igneous rocks we're going to learn how that happens we also have volatiles so volatiles is a perfect example of why geology sometimes might sound like a foreign language because all volatiles really mean our guess it's a scientific term for the word guess so these are materials that turn into gas at the surface so um water vapor um carbon dioxide sulfur dioxide um that's what we mean by volatiles these are these are important in many aspects but in particular we're gonna kind of return to this idea when it comes to volcanic eruption so beginning of this lecture one of the first things i said was that we don't know what's beneath the crust because we've never actually been able to go there there have been scientific expeditions that have tried but the temperatures and the pressures are too high so if i'm telling you we have the crust then we have the mantle then we have the liquid outer core in the solid inner core how could i possibly know that what clues are there that help me kind of come to that conclusion um well we have um earthquakes to help us so when there is an earthquake there's movement along the fault line energy is released that energy is going to travel through different materials at different rates so for example if it's less dense it's going to travel more slowly if it's more dense it's going to travel more quickly if it's solid um both types of waves that are produced both s waves and p waves can travel if it's liquid only p waves can travel through it so after an earthquake we get lots of data and so that's been able to help us build almost like a cat scan of the earth to see what's happening beneath what i'm going to be posting um along with this and i highly encourage you to watch them i'm going to be posting some video supplements these are going to be um giving you additional information about how waves actually impact our understanding of what's happening beneath the earth so they're going to talk about our p waves and s wave shadow zones which we're going to talk about in a minute they're going to talk about the cat skin so these are going to be separate little videos that were actually produced by an institute for seismology in the us but i encourage you to watch them because they'll they'll give you visuals and they'll give you additional information to kind of see what's happening help you understand this concept those will be posted along with this lecture on the same page but i'm encouraging you to watch this so here we have um material here that's undisturbed now we have um material here where we have our directional movement and then our waves moving up and down so what we're looking at here is the difference between key waves and s waves if we think about like a bolt of light oftentimes we'll know that a bowl of lightning has happened because we've heard thunder well thunder and lightning are essentially the same thing um thunder is created by like thunder is the sound waves whereas lightning is the light waves from the same event so when we have an earthquake we have p waves and s waves so p waves and s waves are produced from the same event they just move slightly differently just like we don't see thunder we hear it but we don't hear but we don't the lightning is visual but we hear the lightning through the thunder so p waves are compressional which means they inch their way through a material whereas s waves they move up and down and like in like a sine wave motion up and down we use this data um because of the different motions because this p wave if i had a slinky here i could go inch by inch like an inch form through the material um whereas the s wave is actually moving up and down um the p wave because it's moving like an inchworm it actually travels through solids whereas that s wave because it's moving up and down cannot move through liquids um so after an earthquake so for example in 1995 we have this earthquake in kobe japan we have these materials that um the waves travel outwards the s waves will actually reflect around whereas the p waves will actually refract which means bend so if you've ever put a straw in a glass with water and notice that the straw doesn't look straight anymore or if you've ever been swimming and you've noticed that things above water and below water look different that's what refraction is reflection means that it actually kind of bounces around because it can't go through it and so as a result we get a whole region of the earth where we don't get direct space because of that reflection excuse me where we have that reflection we get a shadow zone for the p waves meaning we don't get the e waves after but because of the way that these waves behaved that's how we were able to determine the density and the state well solid or liquid for the mantle the outer core and the inner core um so this was first really studied by a danish um seismologist um ingrid lemon um she was really the first person to put together in the 1936. um since then we've gotten a lot more data and so that's kind of helped solidify this idea but we have this region here of a p wave shadow zone and then we have the s wave shadow zone and all of this is formed by the different ways that the waves travel through the mantle and the core materials and so this gives us that kind of cat scan version of what's happening on the earth and i'm going to be posting those additional videos i highly suggest you watch them because they do a really good job of visualizing and explaining this material from a different perspective for the s wave shadow zone um that's an area where we don't get the s the direct s waves um so that's how we figured out that there was a liquid outer core because s waves were reflected instead of refracted like looking here um at a cross-section of the earth and now i'm going to kind of take us there by layer through the earth itself um we have the thin ocean crust here and then we have thicker continental crusts and then below that we have something called moho right now we're just focusing on the crust and i want you to see here that how this was drawn the crust is not a consistent thickness there are areas where the continental crust goes further down into the mantle and whereas the oceanic crust is pretty much of evening thickness so the earth has three primary layers the crust which is the outer layer of here think of it as like a candy shell um mantle which is like a silly putty solid um this is the largest volume and it's kind of the pressures and temperatures are so high there compared to the surface of the earth and it's unearthed like in terms of materials that we can think of and relate to on the surface closest materials that we can really think of it as is kind of being like a jello or being like a silly putty it's a salad that flows the salad that moves and then we have the core which is the outer part is liquid and the inner part is solid um continental crust is less dense than oceanic crust and when we start to think about the tectonics and how they move that's going to be critical to understanding how the earth's process so if we think about just the crust itself it's the outermost skin of the earth um with the variable thicknesses so it's going to be thickness it's going to be the thicker underneath mountain ranges and it's going to be thinner underneath oceanic crusts so let's give you an idea of what we're talking about here just to so you can kind of have a perspective so mountain ranges could be like 40 miles thick whereas the oceanic crust is going to be probably about two miles thick um there is an area um that we've been able to use seismic waves to detect where we have crust here we have that oceanic crust here and that layer that transition between continental cross to the mantle we call that the mojo or the mojorovic discontinuity um as you can see in this diagram moho is what we label it as this is marked by a change in the velocity of the p wave so there is an actual physical change in properties but the moho is not a consistent layer all around the globe going to be shallower under oceanic crust and deeper underneath the continental cross because that continental crust is going to be kind of like a hand pushing into memory foam it's going to force that moho deeper so um as i mentioned before there are two types of crust we have oceanic crust and pendancy crust um continental crust has an average rock density of about 2.7 um grams per cubic centimeter and it has an average thickness of about 35 to 40 kilometers on average it has what something called a granite composition so when we talk about igneous rocks we're going to find out what a granulate is but um notice that the density is about 2.7 so granite is a lower density than a rock that the oceanic crust is made out of which is called basalt from celtic composition which has an average density of about 3.0 grams um the average thickness of the oceanic crust is about um seven to ten kilometers um notice that i am using grams kilometers um the metric units because that is what we use in science um the difference intensity is what controls the position so when i say float um i don't really mean floating it's not like it's sitting on top but it floats a little bit higher it's less dense and whereas the oceanic gens floats a little lower so in other words the continental crust is a little bit higher on the mantle material whereas the oceanic crust floats a little bit lower on it um the oceanic cross actually is formed from the mantle itself so it's closer to the manhole composition um we are not forming new continental crust but we are forming new oceanic crust each year um when oceanic crust and continental crust collide the a crust because of its density will actually go underneath it and we call that as production zone so what that would look like i'm going to draw here on the screen if this is our continental cross here and we have the edge of a oceanic crust moving towards it what's going to actually happen is eventually i'm going to switch colors here that oceanic crust is going to actually when it hits it it's going to actually say okay i'm more dense i'm not going to fight you and it's actually going to go down into the mantle and that's what we call a subject um we'll return to this idea when we start to think about ignatius um there are two parts of the crust um and mantle that are distinctive enough in terms of their physical properties that they are given a name the lithosphere is the outermost 150 kilometers of the earth this behaves as a non-flowing rigid material this material is what moves the plates around and it is consistent of the crust and the upper mantle so the moho is also part of this lithospheric portion now the asthenosphere is the upper mantle that's below the lithosphere so the mantle is not homogeneous meaning it's not the same throughout it changes its um composition as you go deeper so the asthenosphere is below the of stereo so the lithosphere does include part of the mantle and the moho the upper mantle that's below the mystic chair is called the asthenosphere um this is shallower um under the oceanic and deeper under the continental this may seem like a familiar idea because we talked about this with the mojo that these that these materials are not the same um throughout the lithosphere is very rigid it's what the plates are made out of it can break very easily whereas the asthenosphere is this that soft flowing solid so we're thinking like a silly putty type picture um so now that we're talking about like the upper mantle well now we've entered new materials so now we're thinking about the mantle over the crust and this is solid rock but it is flowing solid rock which i understand is kind of a weird concept to think about sometimes um this is the layer between the crust and the core it is about two thousand five hundred for two thousand eight hundred and eighty five kilometers thick and it's eighty-two percent volume of the air so this is the largest volume portion of the earth because it is so hot because it is flowing we actually have heat coming off of the outer core that rises up through the material and it creates this kind of movement so if you've ever watched a lava lamp how that lava when it starts to heat starts to rise and then it starts to fall well we have this rising and falling that creates almost spinning in the mantle as a result um it has a composition that's called ultramafic um we're going to talk about this when we talk about envious rocks but that means that it's comprised of iron and magnesium silicates when we talk about um minerals those terms will be more familiar with to you um so this flowing is going to be very important when we start to think about plate tectonics later this term um that flowing and that kind of rotating we call that connection and that happens just like when you have that hot and cold sinking hot rising cold sinking um so if you've ever been in a house in summertime and maybe you don't have central air so or the air conditioning is not working for whatever reason would you rather sleep higher or would you rather sleep on the floor um would you rather sleep in the if it's a multiple multiple story building would you rather be on third floor or would you rather be on the first floor or would you rather be in the basement um cold air sinks which is why basements are often cooler um than say the attic because hot air rises um there are three layers in the mantle i'm not going to really test you on this but i want you to just kind of be introduced to these ideas they're called the upper mantle the transitional mandible and lower so that brings us to the core the core has two layers um the outer core is liquid this is where our magnetic field is actually created and it's primarily made out of nickel and sulfur whereas the inner core is made out of iron and nickel um there's actually an interesting relationship between the flow and the outer core that's generating the magnetic field um and the magnetic field is invisible we don't necessarily see it although i've actually recently read some papers that say birth can see it but that's what creates like a cocoon it creates like a like a almost like a donut around the earth to protect us from the solar rays um so if we didn't have that liquid movement with the electrical fields we wouldn't necessarily have the magnetic fields forming um so we use the seismic waves like the p waves and the s waves to figure out that we had a liquid outer core um we've how do we figure out what materials are down well the change in the refraction does give us an idea we've also used like diamond anvil cells and there are some experimentations that we can use to get high enough temperatures and pressures on a small scale to kind of investigate what might be down there so through these experiments um we've determined that the liquid outer core is most likely um iron nickel and sulfur um it has it's a practically two thousand two hundred fifty five um kilometers think however um think about this the core is cooling down it's losing heat so gradually the inner core which is solid is actually growing and the outer core is shrinking a little bit but not by significant amounts each year um the inner core is solid nickel um iron nickel alloy there are possible other other elements in there for example um there might be some sulfur or oxygen in there um that has a density of 13. where am i getting these numbers from 12 and 13 and 10. um there's a couple different things we do have the experiments we do have the seismic data but we also have um iron meteorites that we've used to determine the composition and that gives us the average density of the earth is about 5.5 well if we remember the oceanic crust is about um three the continental crust is about two um the state is right here so um you don't have to flip back and then the mantle based on the minerals in it it's about 3.5 to 5.7 well if you took just those numbers and averaged them we would not get an average of 5.5 and we know that the earth when it was first forming was forming from those meteorite materials so based on all of the data that we've collected that's helped us determine the density of the core um so the earth's magnetic fields um flow from the outer core and generates it so we have that outer core it's liquid there's actually um electrical fields in there and that movement of the middle helps create that magnetic field this extends out into space so it actually goes around the earth and it helps deflect solar wind this creates our northern and southern lights but it also protects us so if you've ever heard of the news that there's a solar flare there might be some electronical issues um on a certain day or a certain week um that's when the solar wind gets so strong that it actually penetrates our magnetic field if we didn't have a mending field the earth would be in trouble there's a documentary called i can't see what that's called but it talks about the earth's magnetic field and compares it to mars so there's been nasa um nasa sent out um satellites to survey mars and on mars service they saw that the rocks did um record quite a bit of the magnetic field in the rocks but there were two areas where uh meteorites or comets or some kind of hit happens um asteroids where you had two craters one was called helles and one was called our dire when you have a meteorite hit or degenerated so the crust is is momentarily melted then it has to pull again when magma or lot rocks are forming or cooling in a magnetic field gonna record that in a magnetic field it's actually how we track our magnetic storms in the moon video how we track our magnetic fields even here on earth um so when we think about this magnetosphere or this region of this keeping up the solar wind and we think that mars had these areas where they were no longer recording a magnetic field what we think happened was mars because it's smaller than earth lost its magnetic fields earlier than the earth has and so those solar winds actually took away most of the water and most of the atmosphere and that's why it's the red planet and it's not similar to earth whereas our magnetic field helps protect us from those solar winds so we don't lose our water and we don't lose our app um and so that's just um a little bit of the importance of our magnetic field i'm gonna um [Music] share this video with you about the magnetic field our sun is constantly blasting huge amounts of hot plasma out into space all those charged particles have a big effect on everything in their path so what's protecting earth from the solar wind and solar storms earth's thick atmosphere provides some defense scattering and absorbing solar particles before they reach the surface but our planet also has a secret weapon a strong magnetic field that projects into space mostly generated by molten iron alloys moving in earth's outer core the area of space where the magnetic field interacts with the solar wind is called earth's magnetosphere its shape constantly changes as it's bombarded by solar particles as positively charged protons and negatively charged electrons enter the magnetosphere most of them are deflected around earth long before they reach the atmosphere the magnetosphere really gets tested when big solar storms carrying more plasma and traveling at higher speeds are on a collision course with earth while most of the plasma is deflected some of it gets trapped in the magnetosphere and funnels back toward earth along field lines emanating from the poles as charged particles from the sun collide with nitrogen and oxygen molecules in our atmosphere they create the cosmic light shows known as auroras the bigger the storm the further from the poles auroras can be seen some storms are so big they interfere with satellites cause planes to alter their roots and can create other problems [Music] the vast majority of the time these inconveniences are pretty minor but the next time the solar version of a perfect storm overwhelms earth's magnetic shield we might not be so lucky so i hope that video that visualization kind of helps you see the importance of our magnetic shield when some of those ions get around those van allen belts or those um kind of fields if you will the ions will actually interact with our atmosphere and that's what creates the aurora borealis australia the northern and southern lights i've had the opportunity to see faint ones actually when i was in nebraska on geology field trip years ago recently there have been some sightings in parts of michigan and that's just because um sometimes uh um the kind of areas where the belts are closing is rotating a little bit because the earth is constantly rotating um and the earth is tilted um so that's why the aurora flow um so we're going to pick up minerals that's going to be our next topic next week um so i just wanted to preview that for you but i didn't want to start the material yet please let me know if you have any questions remember i am here to help um good luck and i look forward to reading your summaries