GEOL 101 - #14 - Sea Floor Spreading

how's it going good morning everybody welcome to ellensburg washington usa we've already got plenty of people in the room jack looking nice this morning jack sitting in his back row there so i welcome you all today let me give you the local time the local time is 9 49 a.m and we will begin our program on seafloor spreading at the top of the hour at 10 o'clock and i want to experiment with one thing before i forget and then i'll say some hi to some folks okay i'm gonna i'm gonna experiment emily watching this can anybody guess what i'm trying to experiment it could be anything nobody will guess it oh all right let me make cracking myself up on a monday morning let me say hi to a few folks and i'll tell you what i wanted to experiment with there are we doing okay uh actually let me check the camera setting quick he pops out the camera setting like a wide screen and the auto stuff is off okay uh yeah some good mornings uh hello missouri and uh david uh d.c metro hello catherine says five by five so it looks like things are functional here laurie says it's seven by seven it's that good well that's great uh virginia tech no what's vt too fast to see corvallis oregon edmonds washington cincinnati ohio hello john good morning emily too did you drive down from clea alum today yeah how were the roads you take the old road or the or the freeway not a girl okay great aberdeen scotland good morning spokane washington toronto that's adam and uh adam another adam is in sigued hungary good morning good afternoon for you uh germany hello bavaria that sounds delightful norsh feinstein jim in visalia california vermont the students in the room are are filing in oh we got hunter we've got uh hope all people named h i guess they're coming in alphabetically now so before i forget let me tell you my little experiment i don't know if you've noticed but if you watch one of these in replay and you find the show there's my little chalkboard thumbnail thing you know my little black chalkboard where i write out the name of the program but i don't know do you have to like get your cursor over that or something and then suddenly it gives you just a couple of little uh motion shots from the show and uh it's always the weirdest stuff like i i noticed it really kind of for the first time because i did my camouflage thing last time and that's the part that kind of showed up you just hover over it and it kind of went to so i i just wanted to i don't know if it's motion or or what it is that kind of that's what youtube decides to grab but i thought i'd give it a try so yes this is related to today's topic but i'm curious if that will be the thing that automatically shows up what else do you have to say and then i'm going to go visit with the students for a couple minutes um you know i'm forcing it now i'm inter introducing people to each other and they're like i i don't want to talk to that person please don't don't make me turn around talk to that person some of it's happening organically which is wonderful both eve and tawny came in together they've got a class is it math do you guys have beforehand yeah so they're they're already warmed up coming from a math class and we got um one emily coming from cleoelum another from from across campus i guess and uh pedro's here a little early today i'd love to just have you visit with each of these students but can't do that okay couple more finland good morning myra nice shirt thank you this episode of nick from the classroom brought to you by land's end that's the only shirt that i have found that fits me well and feels good so land's end you've got to love it i think it's land's end yeah i think it's landsat uh canterbury uk victoria bc wilmington north carolina portland oregon houston says hello or howdy hope yeah there's somebody from portland right right in there are you from portland i didn't know that are you paying out-of-state tuition not to be too personal no you're getting the wooie you're paying mostly in-state tuition-ish still highway robbery but that's that's better yeah good good what part of portland do you live in okay what's your street address that i can repeat what's your social security number i'll repeat it just kidding i'm glad you're here i didn't know you're from portland uh debbie's husband likes eddie bauer uh all right jeremy's from port uh north carolina tim is from the netherlands gnarly continues to be locked down really miss her shows um okay let me let me get out of the way uh for everybody i've been standing in the way of the outline and we will begin in five minutes thank you for joining us all right kade i'm coming to you today i'm coming i'm coming your way this is going to be casual banter with an older gentleman you got to get your get your head right now k-a-d-e you know i just saw him what's that [Music] oh yeah that's that's him all right it just one of those things that randomly showed up as like a recommendation for you to watch after watching oh oh you watched fridays because you weren't here on friday i got my eye on you okay well that's good you watched pedro barely made it you kind of rolled in a little late didn't you yeah but you did but yeah and then i was like eating my breakfast so fast and i was like watching the thing and then you mentioned like oh you support now [Laughter] that's good so you had the live stream going at home yeah on your phone and then i said what i didn't catch what you see i said did i was i calling you out i'm like oh this is really important oh yeah yeah [Laughter] well i'll remember that next time you're not here i'm gonna say i'm gonna look right into the camera pedro get your ass into this classroom please i know you don't want to come but i'm not going to ask you if you're glad you came but there is a right answer to that question and you're drinking a mulchiado cold brew yeah yeah just a straight up cold brew guy okay good all right kade that was painless you got off the hook because you you said you watched a video about how wonderful i am so we're all is right with the world okay do you have a music recommendation for me today i have not tried skillet yet i don't think i don't i'm a little afraid to try skillet okay so what's your favorite artist band right now i know it changes everybody has menus that keep changing des rocks like french like d-e-s and then rocks r-o-c-s des rocks what genre are we talking about modern modern like indie kind of alt kind of stuff or like what do you know about them they group from a certain area of the country new york all right uh okay i'm gonna give them a try is there a song that i should try to start with no i'm pushing it okay all right never heard of it thank you good tip jordan good morning how are you what hope's got a des rock song she's from portland she's hip hop that sounds like a cool man boy where have i been and then i recognized the cover art and one of them was like i think that's on my villain playlist it's used to the darkness yes it's good are you a music fan jordan so do i a lot that's my favorite just i like to feel sad you like to feel sad you've come to the right place i know what you mean yeah it's it's powerful it's it's sometimes you know the wrong kind of powerful but it's powerful so what's a favorite artist r b artist lately god dang i gotta write this stuff down jasmine sullivan okay no that's good jasmine sullivan and des rock brooks rocks they're not french what's with the name huh the rocks very cool okay this is us today huh oh god no mason again oh boy i wonder what's going on there okay uh it's ten o'clock we're starting okay uh thank you everybody uh i really like this group we've got a a good thing going and this is a big week for us it's not only a big week uh intellectually but it's a it's a big week to kind of push ourselves forward by next week at this time we'll be talking about the details of volcanoes and different kinds of volcanoes around the world different kinds of earthquakes around the world but we need some of this basic plate tectonic information to make that sing to make that work so these are dense lectures i enjoyed the last couple of lectures but this is number three of a set of four lectures and i'm going to quiz you sooner than later because i don't want things to slip away so you saw in your outline that a quiz is coming on thursday and i'm going to do the same thing here and just remind you that this coming thursday i'm going to jump in with another quiz just to make sure we don't let things slip away because this is a a sensitive kind of critical part of our class as i've mentioned before i've taught this many many times and this is kind of the point where we start to lose people and we never really get them back so you're here you're engaged uh you're my favorites just in case you want to know what my scorecard is i'll show you my spreadsheet i'll show you what i got in the office i got everybody's name and it's it's on a big peg board okay and you're all up on the top level right now what the heck all right so quiz number two will be identical to quiz 1 in format single piece of paper first 10 minutes of thursday four multiple choice couple of short answers you'll draw a little bit that's the only twist you'll draw a little bit for that short answer at the bottom of the page maybe you can guess what you might be drawing i don't know and it's going to cover four lectures worth of material starting with crustal deformation in the big hunk candy bar that was thursday friday was last time right talking about the earth interior and pangaea today is seafloor spreading tomorrow is plate boundaries of the world so we're covering a lot of stuff and i will be quizzing you on it on thursday any questions about thursday counties like we did before we'll do i'll show you a little slideshow while you're waiting for these guys to take the quiz on thursday and then we'll do a lecture on thursday so it's just the first 10 minutes that will be weird pedro you got something no okay how's the cold brew thumbs up okay all right uh also just programming note we still have two yellow books that have not been grabbed yet they're free so if you've lost your yellow book or you want i don't know if you need a yellow book we still have them here courtesy of whoever that was i forget that bought those do you still have a syllabus you have a list of the lectures are you flying blind or do you know what's happening three weeks from now et cetera i'm i'm sticking to the plan i'm swiss german so that's not changing so there's that for you as well uh i just checked with zach he was in there this morning in the intro lab room waiting for drop in tutoring nobody showed up okay it's early it's monday whatever but you have opportunities right after class you can get some one on one to get ready for the quiz or thursday morning right before the quiz come in a little bit early visit with zach he's a smart guy they're both very smart guys and they are doing nothing in there they're just listening to music like desrock or jasmine stole stumble out and that's great stuff i can't get over that music okay good are we ready to go hot damn let's do it uh plenty of yellow book today a quick reminder of where we were last time page 17 and 18 was kind of late last time page 17 and 18 was kind of late last time and we decided that page 17 was a look at the earth interior by silica composition no talk of movement and i don't think i hit this point hard enough last time we still don't know very much about the interior of the earth i think that's a safe statement to make i'm particularly weak on geophysics and the earth interior when i was done with you on friday we did a little live q a with the home audience and i wasn't answering any questions because i didn't know how to answer their questions but even that means that we really don't know much about the detail but what we do know is substantial as far as these boundaries are concerned especially the moho which is the sharp boundary between the crust and the mantle more silica in the crust than the mantle we know that because of seismic wave velocities quick call right off the bat the seismic waves travel faster through the mantle of the crust come on now mantle eight kilometers per second through the mantle six kilometers per second through the crust there is no gradual ramp up it is a sharp contrast between the two but that didn't help us with plate tectonics notice that our outline today the first thing we're doing is trying to decide what the difference is between a continent and a plate that's a big question and one of the ways we answered the question was realizing on the next page page 18 it's the same planet and yes we could superimpose the depth of the crust and the moho and the mantle and everything else this is the same planet but on page 18 we're ignoring the crest mantle core and instead we're focusing on rigid cold blocks of lithosphere called tectonic plates separated by these red lines which we're going to realize tomorrow are plate boundaries and then a big point before we quit is that the asthenosphere is solid also but it is movable it is flowable it is plastic it is ductal and so if we have this magic asthenosphere layer that allows movement then we can break these blocks of lithosphere free make tectonic plates and the tectonic plates can have minds of their own they can move in different direction that's exactly what we've got okay energy's good for monday morning keep it up brand new stuff page 19. i have an assignment for you are you going to turn it in no but it's an assignment for you page 20. is that what this is no no i'm 19. i just said 19. page 19. this is a plate map of the world and we need to learn it we need to learn about the major tectonic plates of our planet because we care deeply now from this point forward about the size the direction of these tectonic plates and we care much less about continents so continents and plates are completely different from each other totally different concept and we're trying to make the fig make that work what's your assignment we got six major plates the two american plates the eurasian plate the african plate the australian plate and the pacific plate ignore antarctica ignore the tectonic plates that i have more struggle today with the document camera ignore the unlabeled plates that i have for you but you can see those black lines michaela get off the phone those black lines are plate boundaries again tomorrow is going from black line to black line to black line and making sure we know what's going on at those black lines i'll give it to you right now almost all earthquakes and almost all volcanic eruptions happen at plate boundaries almost all earthquakes in almost all volcanic eruptions happen at these plate edges at these black lines they don't happen generally in the middle of the tectonic plates actually the new madrid no we're not doing that we're talking about global patterns we're not talking about the exceptions so we care about these plate boundaries so for the six major plates please commit to memory the direction that they're moving you have arrows what's the direction that they're moving i'm giving you an assignment three things for each major plate direction they're moving percentage of ocean crushed versus continental crust and some geographic examples for the edges of the plates that's wordy so let me give it to you one more time i think if you do this little verbal assignment you will be sitting pretty for the next week and a half for each of these major plates what's the direction how much ocean versus continent and can we find ourselves when we're at the edge of one of these plates let me give you an example the north american plate moves west that's our plate the north american plate moves west in a couple weeks we'll realize that's kind of a lie it's not exactly straight west but for right now that's fine okay we have a north south moving west just eyeballing the north american plate hopefully your geography is strong enough where you can see where the continent of north america is versus the ocean of the atlantic ocean i'd say north america's plate is about 60 percent continent and 40 percent ocean i'm just eyeballing that's all i want you to do too you're just eyeballing continent versus ocean for each of the six major plates the pacific plate which kind of goes you know it's kind of split by the edge of the map here the pacific plate is our largest tectonic plate and it's 99 ocean plate but there's a little bit of continental crust on it there's a little bit of continental crust on the pacific plate los angeles california for instance is on the pacific plate but it's continental crust and an example for the third thing the geographic boundaries or whatever i just said uh san francisco california you could pick a city you could pick a mountain range so san francisco california is on the western edge of the north american plate so keep your eyes and ears peeled for little examples like that today and next time that you can add to it are we clear on what i'm expecting you to do for that it will pay off big time on thursday and also in the midterm coming down the road so i want to do some drawings just too static right now i want to do some drawing with you on the other chalkboard and i want to draw a big sketch for you to very clearly illustrate not only the difference between a plate and a continent but it will also get us into today's topic called seafloor spreading are we good feeling okay again thank you the energy i don't it may seem weird to you that i keep saying the energy is good or the energy is terrible i've been doing this a long time i can feel when we're connecting and when we're not i don't know how to describe it scientifically but i can just feel it and i can feel it right now so let's thank you for that okay you got marie's name you got the the layout today i'm not going to pause anymore okay so give yourself plenty of room big sketch do a lot with it it will correspond i'm going to go quickly now i want to just kind of keep building on the pace that you have with me all right you know this business of using the chalkboard is a nice throwback to the days i used to only have chalkboards so it feels like it's i'm 20 years younger i wish let's put a boat in here huge person okay uh so again if there's a big sketch that i say give yourself plenty of room it's always a good idea to jot down a title or at least a statement like why what's the purpose of this sketch in this case we're trying to elaborate on the difference between a tectonic plate and a continent so we're in the first of the three parts of our lecture today okay i told you i was going to go quick here we go here's new york city here's san francisco california so this must be the north american continent here and it is you can it's about 3 000 miles to drive from sea to shining sea this land is your land this land is my land etc okay san francisco to new york city north america's continent now we can do the same thing with the eurasian continent uh tokyo japan a city called lisbon what country is that in thank you portugal hope is that you good so this is the north american continent between these two cities this is the eurasian continent between lisbon and tokyo and this is of course the atlantic ocean a body of water between new york city and lisbon portugal i don't need to label it do i the atlantic ocean but notice i also have a cross section here so i have a look underground and we're applying page 17 and 18. some of you are ahead of me great this is a depth of zero kilometers depth it's a surface this is a depth of 100 kilometers again some of you are ahead of me i'm off the document camera so what did we learn on page whatever it was page 18 a lithosphere is 100 kilometers thick correct around the world is it page 18 yeah so this is showing the depth to the base of the lithosphere and this white line this white line and this white line are those pink things that i drew last time you can see it now can't you so i emphasized last time that if we can somehow break the lithosphere into blocks we can have a tectonic plate that's what i'm doing so graphically i'm showing you the difference between the north american continent and the north american plate here's the north american plate it goes from this white line to that white line that's one continuous block of lithosphere what's the depth 100 kilometers depth what's below it a stenosphere and this is the eurasian plate that's not the same thing as the eurasian continent so it's time for you how would you put into words the difference between a plate and a continent try not to overthink it how would you put into words they're not the same so how would you put it into words the difference between a continent and a plate anybody come on we can do it uh emily too beautiful there's plenty of ways to answer it but that's the most basic and beautiful way at the moment emily nice job what is the north american continent really it's a portion of the north american plate that's above sea level continents are portions of larger things called tectonic plates a continent is just a portion of a plate and it's the portion that you can build houses on so yes this is the north american continent but this is the north american plate stretching all the way from san francisco past new york city and out to the middle of the atlantic ocean yes there is a mountain range underneath the waters of the atlantic ocean do you want to crane your neck and look at oh tim's not here either you can see that world map that tim was showing us last time can you um cade you're on can you pop up come on kate where's the atlantic ocean cade correct uh do we see what's in the middle of the atlantic ocean okay can you drag your finger down the middle of the atlantic ocean and look at yes that thing right there do you see that that's a mountain range you can see that the the whatever color that is it's a little bit lighter in color going down through the middle i'll show you some professional maps in just a second uh created by marie tharp that's why her name is on the outline today thank you that's the mid-atlantic ridge you have it on your outline i'm not going to write it out the mid-atlantic ridge a perfectly named mountain range it's a mountain range it's a ridge that's almost completely underwater and guess what it runs right down the middle of the atlantic ocean so in the case of your little assignment for page 19 the north american plate has this san francisco on the west edge and the mid-atlantic ridge on the east edge let me give you more does somebody want to guess what the name of this white line is if it's right beneath san francisco come on oh no what's the name of that white line it's a crack that's underneath san francisco california i'm shocked nobody has it the pacific plate would be on the other side of it i'm asking for a what i thought was a pretty easy question about the name we have some michaela very close okay so now i'm realizing okay we haven't had a big earthquake on the san andreas fault for a long time the san andreas fault and i think that's part of the reason that didn't obviously come to your mind we we haven't had a tragedy in a while of course we'll talk about earthquakes and tragedies are coming but you're young enough to not remember the last big earthquake 1994 northridge is probably the last significant one that we all remember but there there's been many so um i didn't mean to belabor that but here's another way to say it the north american plate is between the san andreas fault you're like i'm not even sure i've heard of that well here it is we'll have a whole lecture or a portion of a lecture on the san andreas fault coming next week i guess it is san andreas fault that was meant to be an easy question and then let's try another one i don't know if this is going to go any better is there a place where you can live on the mid-atlantic ridge it's mostly underwater but the answer is yes there is a place you can live and develop a drinking problem and live on the mid-atlantic ridge what's the country thank you hope iceland which we will talk about a fair amount today is a rare time or rare place where the mid-atlantic ridge is tall enough to get its neck up above sea level so we can also say the north american plate the north american plate runs from the san andreas fault out to iceland or san francisco out to the mid-atlantic ridge or any combo of those do you see now the difference if you didn't before the difference between a continent and a plate okay now let's get what i consider to be the most interesting part of today how is it possible no uh last time what was pangaea supercontinent last time when did pangaea start to break apart how many years ago pedro 200 million years ago pangaea started to break apart which two cities were suburbs of each other you know what i mean they weren't around 200 million years ago right which two cities were suburbs of each other 200 million years ago on this cross section pedro new york city and lisbon portugal were suburbs of each other 200 million years ago some of you are nodding furiously you get it others are like uh what uh and that either either reaction is great but you remember last time don't you there was no atlantic ocean during pangaea as quote unquote recently as 200 million years ago there was no atlantic ocean and i'm not just saying there wasn't this is getting interesting now i hope i'm not just saying there wasn't any water i'm saying all of this crust all of this lithosphere no i don't want to i don't want to screw it up all this stuff here all this stuff here was not there significant parts of tectonic plates were not there during pangaea so and again i want to do more with this so i'm not going to mark it all up but this new york this lisbon we're together and so the cool thought is what the hell has been going on sorry patrick what the hell has been going on in the last 200 million years you bring some water in okay whatever i guess but you're actually creating all this crust as well you're actually making lithosphere yes well tell me more about that you say well it's a little process we called seafloor spreading and it's the title of today's meeting do you want to ask anything right now before we get into the details of it all right somehow yeah please uh christina right yes yes i'm not only saying that part of the ocean floor was not there i'm saying that i'll rephrase for christina and probably everybody thank you for that the north american plate was smaller 200 million years ago the north the eurasian plate was smaller why not that was the eastern edge new york city was the eastern edge of the north american plate 200 million years ago lisbon was the western edge of the eurasian plate 200 million years ago and somehow through some sort of process and we need evidence for the process by the way it can't just be an idea we need good evidence as well somehow we're going to create all of this plate material and it's not going to be overnight to add to the size of these plates thank you christina okay um freelancing here a little bit uh we're gonna do more with that but let's try a couple of images to get us there so there's a story that has used to be kind of a fringe story and now is more of a mainstream story because because of a lot of things but marie tharp is the subject of the story you have her name on the outline and she would have been a hundred this year she's no longer with us but she was a very important scientist a very important geologist post-world war ii but she was a woman and her ideas in her work was honest to god discarded as quote unquote girl talk i'm not making this up unfortunately she was not allowed to go on these research ships to contribute to making maps of the atlantic ocean floor but the work speaks for itself and thankfully we've made some progress not enough that we've made progress on including any smart people we can get our hands on wrong phrase there we're inclusive now we weren't inclusive 50 60 70 years ago okay so you have this map we're coming back to it but about the time that marie was plotting some of the data to actually make for the first time a map of the atlantic ocean floor a colleague of hers at columbia university in new york noticed that when you plot earthquakes on a world map they're not randomly occurring most earthquakes are happening in these weird lines and most interesting for us right here i'm not flipping you off right here is the middle of the atlantic ocean and these earthquakes keep happening right down the middle of the atlantic ocean it's like what is going on out there so marie took all this sonar data uh let's not get hung up on it but it's basically a new way to make maps of the oceanfront remember i was talking about post-world war ii and we had all this technology sonar is the actual word so you're you're you're you're um again look i could spend 20 minutes on that i don't want to there was new data coming in about what the bottom of the ocean looks like in the atlantic and marie was the first even though she wasn't allowed on research ships she was compiling and drafting and drawing beautiful maps of the ocean floor and for the first time she showed that this mid-atlantic ridge was a thing and this is her famous that eventually became a worldwide map so this is her famous map her main contribution uh to our understanding of planet earth she made a bathymetric map have you heard that phrase before bathymetric you all learned how to read topographic maps in the lab the last couple weeks this is this is like a topographic map for the underwater and we still know hardly anything about the ocean floor by the way so this looks like a finished product it's not it's just based on the evidence we have thus far but please note that coming right down the middle of the atlantic ocean is this incredible mid-atlantic ridge and there's another one of these incredible underwater mostly uh ridges or mountain ranges called the east pacific rise so you have them both on your on your pro on your outline and let me give you a couple things to write down it's the mid-atlantic ridge and the east pacific rise where this seafloor spreading is happening and i don't want to screw around much more i always want to give you a bunch of statements it's not the most creative way to teach but i'll be back to freelancing here in a second i just want to make sure we've got some some statements we can hang our hat on so seafloor spreading is happening at these two mid-ocean ridges we call them we call the mid-atlantic ridge in the east pacific rise mid-ocean ridges sometimes we call them seafloor spreading centers you get the idea and you can connect a few dots here with what we've done already we're actually going to be creating plate material at these two mountain ranges yeah there's other spreading ridges as well we don't care about them in this class we care about the mid-atlantic ridge in the atlantic ocean and the east pacific rise in the pacific ocean thanks to marie tharp's work we know about those two mountain ranges we didn't know anything about them before what kind of rock is being created at these two spreading centers do you have a guess what rock name it's igneous um maybe i haven't said it yet it's basalt you remember the basalt lava that was the brown stuff that we saw exposed the pre-cut and ready to be hauled off by the ice age flood stuff all of the ocean floors of the world are made out of one kind of rock it's an igneous rock called basalt you know what it looks like when hawaii volcanoes erupt it's orange and middle of the night and it's hot and steamy and everything you got your hawaiian shirt super dorky that's basalt and that's what's going on all over the world in a true oceanic setting so these mountain ranges these spreading centers these mid-ocean ridges are made out of basalt and i'm coming to you in just a bit so if two-thirds of the earth's surface is ocean and that's true then two-thirds of the earth's surface geology-wise is basalt and that's true basalt is by far the most common of all the rocks on planet earth so we're creating ocean crust in these oceans and we're creating it by a process called seafloor spreading and you're like i don't know did i did did the guy talk about seafloor spreading it he keeps saying that i don't know what it is we haven't gotten there yet i'm just trying to lay things out for you so now you can see you know alfred wegener remember the guy last time talking about continental drift and the and the capital letter s on the coastlines of the americas in europe and africa he would have been absolutely hysterical with happiness what if he had the information about there's an actual s-shaped mountain range under water that matches his s-shaped coastlines and so by making these discoveries on the ocean floor marie tharp and a few other dudes somebody said well wait a minute let's go back and read that work by that that german dude alfred wegener everybody said the guy was a joke but i don't know we're finding this stuff on the ocean floors and it's kind of it's kind of sounded pretty familiar from what this alfred guy was talking about at least with this coastline jazz all right so i'm coming to you now i've got a couple maps i gave you a sneak peek of but i want to come back here and i want to involve you now hunter hunter asked what happened to the ridges when pangaea forms that's an excellent question i'm going to give you a partial answer because we're not totally ready for it yet we don't know yet in this class about subduction that's next time some of you might know about subduction but let's hold off on that but thank you for the question hunters like wasn't there a time before 300 million years ago when last time we were putting pangaea together and the answer is yes so i have to answer it kind of the answer is we're going to destroy all this old ocean crust so ocean crust is made by seafloor spreading in a process you'll see in just a second tomorrow we'll see how we can destroy or get rid of ocean crust the basalt so hang on till tomorrow to totally see how that works great question thank you keep them coming okay i'm involving you more than hunter's question based on what i've told you so far what kind of rock is all this stuff that's a softball what kind of rock basalt before marie's work and others work in the 1950s and 60s everyone assumed that the ocean floor was flat that the ocean floor was basalt and that the ocean floor was all the same age like original crest of the earth kind of stuff now based on what i've given you so far what's your prediction for the age of the basalt on the atlantic ocean floor is it all the same age number one no it's not so even though you're not totally sure what seafloor spreading is do you have a hunch if we start go collecting pieces of basalt on this atlantic ocean floor do you have a hunch what kind of pattern we might find if it's not all old what is what would you want to think is the scene for the age of the basalty of the atlantic ocean floor anybody know where i'm headed with this hope we're heading to we're heading to this we're heading to thumbs so the idea of seafloor spreading is a visual that was created in people's minds after they found the data the data is not all this basalt is the same and hope is correct the basalt is youngest out in the middle of the ocean here it is finally you're all here you're all with us i'm giving you data now from what we learned about the ocean floor the basalt has an age pattern the basalt of the atlantic ocean floor has an age pattern i'll do it this way north america this is a map now uh africa you're looking down from heaven it's a map here is the mid-atlantic ridge and i'm dashing it because we're looking down through the water of the atlantic ocean and i'm going to put one island that's truly an island it's above sea level that's iceland iceland is a portion of the mid-atlantic ridge that you can live upon there's a few others as well what is the age pattern that's a zero the basalt at the crest of the mid-atlantic ridge is zero million years old meaning it's it's being formed this morning we can go to the crest of the mid-atlantic ridge from iceland all the way down to antarctica and we could observe hawaiian-like basaltic lavas coming out of the ground and chilling and forming basalt today this morning but if we go x number of miles to the west and the same number of miles to the east i'm just going to pick some numbers here we can find some basalt on the atlantic ocean floor that's 50 million years old and the same distance away from the mid-atlantic ridge on the other side 50 million years i'm just picking numbers now i think you see what i'm doing the basalt on the atlantic ocean floor amazingly and very excitedly in the 1950s when this work was being done we realized there was a pattern and in words the pattern is the basalt on the atlantic ocean floor gets older in both directions away from the mid-atlantic ridge there's a it's like the butterflies wings it's a perfect mirror image the the two wings of the butterfly so the body of the butterflies right down this the spreading ridge and we have matching wings if we're talking about the age we're just talking about the age i mean it's just all brown lava rock you can't look at it and say that's old and young but if you collect samples pull them back up to the ship get into the lab do some absolute age dating you can get this pattern and this goes all the way back for our purposes let's use 200 to be nice and simple right off the coast of new york i'll put new york city on here if you want let's put lisbon and we'll put eurasia and africa we'll put lisbon portugal right here we'll put new york city here and so just off the coast of new york city there's 200 million year old basalt and there's a matching 200 million year old basalt just off the east coast of europe you've got it now and so what do you do with that data how do you come up with an explanation for why the ocean crust is getting progressively older as you get farther and farther away from the interior or the middle of the atlantic ocean you come up with this process called seafloor spreading do you have one significant piece of evidence for seafloor spreading i just gave it to you an age progression of basalt getting older and older in opposite directions away from the mid-atlantic ridge by the way same pattern for away from the east pacific rise in the pacific ocean same idea it's brand new basalt that the east pacific rise and it gets older and older and older in both directions away from it we could spend a whole course talking about all the data that we have on the atlantic ocean floor but i just want to give you one more do you remember from midterm one what evidence do we have there were 33 advances in 33 retreats of the ice worldwide we went to the deep sea sediment do you remember the little skeletons falling to the bottom and looking at the percentage of the amount of o16 in each layer of shells uh what nah i don't have time i don't know if this is even gonna work if you think about it this should make sense what i'm trying to show is deep sea sediment made out of a constant snowing of dead shells onto the ocean floor and i'm trying to show in a kind of a half-assed way that the thickness of that deep sea sediment increases as you go away from the mid-atlantic ridge if you really think about this this should work let me give you the statement again and terrible the thickness of the deep sea sediment increases or the the deep sea sediment gets thicker on the floor of the atlantic ocean in both directions why is this well the older the ocean floor the more time we've had the shells falling to the bottom it's like i don't know what's the driveway look like it's been snowing for a day okay been snowing for a year okay constant snowing that's the idea here too so let's find some of those professional images to back up what i was trying to do in a pretty half-assed way on the chalkboard and then we'll uh put this all together good you can see it pretty well and so can the home viewers so there's a world map including you can see that faint blue there's the east pacific rise and there's the mid-atlantic ridge oh damn oh god that's that's nice that's about as that's about as sexy as i get with transitions let's do that again ready one two three oh damn okay so this is a pretty famous map and the colors correspond to age of the basalt so the red is young basalt and as we get to green and then eventually blue we get into older and older basalt is that what you kind of had in mind from the chalkboard work i hope so by the way still haven't showed you what seafloor spreading is but i hope you can see that the color patterns are different in the atlantic than the pacific how are the color patterns different just think like a first grader now how's how these colors different in the atlantic versus the pacific this is the pacific that's the atlantic how are the colors different yeah that's true there's there's there's all i'm all and thank you for participating the only thing i'm going for is that the bands of these colors are wider in the pacific than the atlantic and before we quit i want to ask you why that is but we need to see what seafloor spreading actually is here's a cartoon showing the can be the mid-atlantic ridge if you want and this does that look like orange to you that orange is the thickness of the deep sea sediment so there's that's what i was trying to draw the deep sea sediment is getting thicker as you get away because the the basalt beneath the deep sea sediment is older okay here we go no sound on these but here is the process then of seafloor spreading that we have in mind the concept is you're constantly sending asthenosphere to the surface at the mid-ocean ridge and it's a constant process of creating crust making basalt but then this process continues so you split that new batch of basalt into two halves you crack it you move it away and then you send more young material into the middle why didn't i put that on a loop let's try it again do you have questions this is your first look at our idea of what's going on at both the mid-atlantic ridge and east pacific rise this model explains all the data that we have from the ocean floors of the world most famously the basalt getting older and older in opposite directions away from the crest you want to see another one there's narrations and sexy jazz and everything but we're i'm i'm robbing you of that experience is this one going yeah usually there's a ton of questions right now do you not have any don't mean to shame you but it's been a good session we only have a couple minutes left so when you go to ice michaela uh yes they're just trying to show lava coming up and extruding out of vents or cracks let me take your question and go a different direction with it what kind of faults must we have in iceland that's a significant question what kind of faults do we find in iceland there's only one answer so the first question is do we remember what kind of faults we have uh oh now we're doing what i promised we were going to do i was going to take stuff from previous lectures and use it that's what we're doing right now this is two days ago you got the question written down what kind of faults in iceland okay so let me help you remember what what are the two kinds of faults normal and reverse is this a normal or reverse fault it's a reverse hope why correct we know it's a reverse fault because the hanging wall is going up with respect to the foot wall these are rules we committed to memory a couple days ago and hope remembers that we have reverse faults when we compress the crust so do we have reverse faults in iceland no we don't because look what's going on come on loop yourself brother what am i doing i'm looping we have nothing but two plates diverging or going away from each other and so the answer to the question is normal false galore in iceland so i'm doing something that we'll be doing for much of the rest of the quarter we'll be taking faults which are smaller scale features and connecting them to larger things like moving tectonic plates so if i'm losing you and you've run out of gas we've got two minutes left give me two more minutes i'm saying that because the crust is being extended in in iceland we have earthquakes in iceland regularly and those earthquakes are when we have hanging walls drop with respect to foot walls therefore we have normal faults the answer is normal nothing but normal faults in iceland nothing but normal faults all along the crest of the mid-atlantic ridge in fact along the crest of the mid-atlantic ridge there are valleys the size of the grand canyon the rift valleys the the the mountain range continues to get pulled apart and so blocks of the summit of the mid-atlantic ridge structure continue to drop now before i lose my time with you oh boy what uh i had unfinished business what was it was that it maybe that was it i guess that was it i think i wanted to do that so i think that was what i had as unfinished business with you uh i'm i'm still waiting for a couple of questions that usually pop up but since they're not coming i will ask myself questions in the one minute that i have does this mean that iceland is getting bigger and bigger and bigger that this island will get taller and taller and taller because i think what you're saying ned zenger is that as we continue to pull these two plates apart we're allowing asthenosphere to flow to the surface and that is true seafloor spreading is this process of taking this tectonic plate and this tectonic plate and pulling them apart from each other and allowing this asthenosphere because it's flowable surged to the surface however the way we view seafloor spreading the answer is no iceland is not getting taller and taller and taller this isn't 200 million years of building iceland because why because with those animations i hope you saw that we continue to pull the crushed apart horizontally and so if you look at iceland it never really totally gets bigger and bigger and bigger i mean yes it's tall enough to get above sea level but we don't view iceland as getting taller and taller and taller because we keep cracking iceland and pulling it apart and sending new material in its place and by the time you move the ocean plate off of this active plate boundary you lose heat and if you lose heat you could use you shrink or you condense the crust so the view is and this is a more advanced thought all of these places on the atlantic ocean floor originally were at a higher elevation at the mid-atlantic ridge but they have been cooled sunk onto the ocean floor and by looking at the amount of time we're talking about with forming the atlantic ocean floor we know about the timing of breaking apart pangaea it works beautifully together oh i you get i'm already two minutes late sorry the thing i did want to circle back on i don't want to take the time why were those color bands wider in the pacific than the atlantic does anybody have the answer why are the cut we can do this why is why are the color bands showing age wider in the pacific than the atlantic both have brand new material at the summit so that's not quite the answer aiden correct the sea floor spreading in the pacific is moving faster than the sea floor spreading in the atlantic these color bands are wider in the pacific than they are in the atlantic because the rate of spreading it's spreading fat the specific rise is spreading faster than the mid-atlantic ridge and you're like why like don't know and then a more interesting question is why is the atlantic ocean getting wider if it's spreading slower than the east pacific rise and for that answer you're going to have to come tomorrow go to the exits now thank you thank you thank you for coming thank you for spreading away from your desk and going and subducting into your dorm room what appreciate you coming today i hope you're feeling the payoff for coming to these lectures as opposed to staying home in your jammies and watching it on youtube or playing video games and not getting a damn okay i'll be with you in a second thank you for joining us as well anybody need a yellow book you've got a refund i hope uh no because i had already written in it like from the online classes oh really yeah i didn't want to try to return it when i had already written it you know but i mean i don't mind it was only eight bucks i just liked it well yeah casey thank you um look at your account it's not a return thing it's just them crediting the people that that that bought it so so i i think you were credited the nine dollars or whatever it was but but you let me know if you look that up and it's not there yeah okay good thank you you bet young lady thank you for participating today what's your name karen the first time we heard you in class second well keep it going keep it going that was a good ad there today thank you karen okay townies i'm coming okay room is empty it's just you and me let's do a little live q a i might have some answers for a change uh uppercase if you don't mind we're still working barcelona back from the hospital how far north does the east pacific rise extend well north america is the answer and that is a major part of our discussion uh in a couple of weeks so the east pacific rise heads right for baja california and and looks like it goes right beneath nevada and uh so that's the answer i don't want to get too far ahead of our class here but that's my answer there okay you know how i operate when i see a bunch of uppercase i just start scrolling between live and back and i try to answer as many as i can in a relatively brisk manner papagino if ocean ridges are spreading on both sides of south america where is it subducting well maybe a lot of these will be out you'll have to wait but i i feel like i don't want to do that to all the questions yes they're spreading here and they're spreading here but as we'll discuss tomorrow in class there is a subduction zone off the west coast of south america and subduction is where we destroy ocean crust so this is a sneak peak to how we'll start tomorrow even though the east pacific rise is spreading faster it's also getting its crust destroyed all around the margin of the pacific ocean something called the ring of fire everybody loves that concept of ring of fire or some people say rim of fire so because we're not subducting the atlantic ocean crust that's why we're moving north south america west thank you has this uh worm a hand has the spreading been the same speed the whole time um to answer that which is work that's been done you look at a bunch of things but you also look at the width of these color bands and if you have wider color bands like look at green here green is is wider than orange for instance and i think well i'm not even sure now not wrong so i thought maybe the color bands were laid out perfectly by time but they're not so i guess the simplest way to answer it is generally yes but i think there are ways to document when a spreading ridge accelerates or decelerates but now that i say that i'm not even sure that's true good question so iceland jackie so iceland will eventually have an ocean in the middle of it i wouldn't think of that either so you heard my message that quite uh again there's there's such a fraction of the normal room there's usually 100 students in here so i'm used to the same every quarter i mean the faces and the names change but you could just almost like plan on when somebody's going to ask a certain question in some of these lectures but we've just got so many it's a great group but it's small so they're just not anyway so usually people say you know iceland is are we going to get a hole the common question is are we going to get a are we going to get if we continue to spread on the mid-atlantic ridge this is a common question are we going to get a like a ridge like a whole place where people can build new cities and stuff you know like this whole thing emerging out of the water and and then i talk about this rifting and this pulling away and this this sinking but you're going the other direction where you're visualizing a big ocean forming in the middle of iceland i wouldn't think of that either because we continue to have this new basaltic material creating so i'd visualize a continual it's kind of a weird concept isn't it i'd visualize a continual ridge for both the east pacific rise and the and the mid-atlantic ridge but i would visualize a recycling of material but keep the knuckle like this but recycle material through it larry is lava always a stenosphere material rather than mantle kind of the same difference larry so that's where we get hung up between terms so the asthenosphere is mantle material again the mantle is a chemical term and we've have low silica magmas coming out when that is a cenos for material so it's the same stuff the stenosphere coming up is mantle material coming up uh sabre did the spreading ridge start on land in pangaea yes so some of you know that nevada in the western united states is rifting right now that's called the basin and range province and we're stretching that continental crust and we're forming normal faults from the stretching and then if you go the next stage of that is developing something like a rift valley like a big rift valley like in eastern africa so you take nevada and then you stretch it more it becomes uh eastern africa and then if you keep stretching eastern africa then you eventually get a spreading ridge and some basalt ocean floor and then you do the whole thing so what i'm saying is when new york and lisbon used to be together it was nothing but content you could walk from from new york city to lisbon portugal and then you go through these stages of nevada basin and range then east african rift and then you finally have something like the red sea or something um peter what's the difference between fault and fissure faults produce earthquakes faults produce earthquakes by having blocks of crust slip suddenly and fissures quite often are cracks that are not producing earthquakes and fissures are also quite often extensional where they literally are opening the crust and allowing basaltic magma to come up we'll talk about fissures quite a bit when we get to the columbia river basalts so it's an important distinction dog knee why is why is it a rise in the pacific in a ridge in the atlantic yeah i don't know i wish they were called the same uh um no significance they're identical structures just a naming thing joe is the antarctic plate considered static i guess i don't really know that much about the antarctic plate and for our purposes with geology 101 it's just convenient to ignore that antarctic plate when they're spreading ridges it's just too hard i don't know it's too hard for me to visualize and therefore too hard for the students i think i think it's safe to say although somebody can correct me that the plates are not moving as fast at the poles than they are at the equator is that right i'm not sure death mall why is hot magmas strong enough to push an entire plate worth of cold dense crust i i failed to mention that i usually get to that point thank you i'll try to remember to start tomorrow with that you remember my message that i'm not sure we understand why plates move and it's a common mistake for people to say that magma coming up at the mid-atlantic ridge is pushing the plates apart i don't think that makes any physical sense so i take your i take your question to heart i don't see how a little bit of asthenosphere leaking to the surface is going to push a tectonic plate but i'm no mathematician so yeah i want to downplay that concept if people are connecting the dots on their own and assuming that sea floor spreading is pushing the plates that doesn't make any sense to me something bigger something stronger something more profound is driving these plates and i visualized these two plates being driven away from each other and then the seafloor spreading is this is just a stenosphere or mantle coming to the surface and taking advantage of that opening run to daylight jerry cramer jay is the san andreas fault moving into nevada yeah it's it's leapfrogging its way from the current position to the walker lane and the eastern california shear zone and then eventually going to nevada but that's beyond our 101 class will california landslide away slowly over time like what happened this past week portions falling into the ocean let's wait until that san andreas lecture talk about an urban legend that will not die let's hold off on that one david can you so you can have a north american plate frame of reference or a pacific plate frame of reference yeah i don't know david um elaine newton's third law for every action spreading there's an equal and opposite reaction plate motion you know charlie says ivan ivana told me plates are mostly pulled down not pushed out well that's that's that's a leading idea these days tomorrow we'll talk about subduction and the concept that just like you have a tablecloth on the edge of a table as soon as you have a lot of that tablecloth hanging over let's say you have more of the tablecloth hanging over the edge of the table then you do have tablecloths still left on the table you're eventually just going to have the momentum of that tablecloth falling pulling the rest of that tablecloth off the table but my question is is that quantitatively backed up i'm not sure it is and if we look at the history of science and we look at the history of geology and we keep looking at all the data that we have all you have to do is just look at the last 70 years about ideas of why global observations how to explain that data i'm just not sure slab pull is is where we stay for the next 150 years that's all i'm saying i'm just saying the final frontier one of the major final frontiers is the earth interior i think they're going to look back on us in 2021 and laugh their asses off whatever the version of youtube is 70 years from now they'll somebody will find this lecture and go what a joke what's with the scarf kent asking about lake superior see what i mean there's there's certain things that just people are fascinated by and uh i don't have much to say s bishop any current new research being done on how plates move i just tried to describe that i don't know about new motion see this is this is um you know that i stay in the pacific northwest physically and also with the stuff that i teach it's it's rare that i do stuff globally obviously i'm doing global stuff with these students because we're trying to introduce plate tectonics but it won't be much further in this class it won't be much longer in this class before we we stay in washington for good and i say that because i'm kind of proud of the fact that i've done a lot of different kinds of programs for washington geology like i feel semi-fluent between geochemistry and geomorphology and seismology and volcanology and all sorts of things and i feel like that's rare quite often people just stay in their sub discipline with geology and you know they go to the grocery store and says hey you're a geologist let me ask you about uh turbidites and they're like i'm a i think about turbidites i'm a groundwater you know chemist so within geology the the tendency is to to stick to your own to stick to that narrow region this is a long-winded answer to say i have a hard time keeping up with geophysics and there must be all sorts of people around the world doing very interesting stuff with seismic tomography only a portion of that work is intersected with my world because of the history of subducted plates here in the pacific northwest and i'm talking about stuff that i did before christmas at home with the live stream series and exotic terrains but i have only so many years left and i want to keep building on washington and what i know and what i continue to learn but of course there's lifetimes worth of work that could be read and dissected and delivered but i'm just one guy i'm down here to live now i'll try a couple more if you want to re-type your question if i haven't gotten to it yet sabab is seafloor spreading speed equal to subduction speeds in general yes again we'll talk about subduction tomorrow the way i'll present it is yes and i don't know how to present it otherwise so i think my answer is yes why is basalt the rock that's formed rather than some other type of igneous rock thank you chris well that's a little sneak peek into our discussion of magma types and different kinds of volcanoes and the difference between oceanic crust and continental crust so that's there's more of a planetary geology approach which i don't have for you but the short answer is if you get mantle up to the surface the mantle has low silica compared to the crust and so if you're making volcanic lavas out of mantle material it's going to be basalt three more sharon are there convection currents in the mantle i'd put that in the cut i guess the answer is yes i really i really don't know enough geophysics to really understand the data to to prove that that's a thing i think you're asking because a lot of people have been taught or maybe they teach or maybe they just assume it's common knowledge that what's the what's the story radioactive decay in the mantle provides the heat to therefore have convecting cells within the mantle and then blocks of the lithosphere are above these boiling it's like boiling water and you've got these convecting cells in the pot of boiling water and then you throw in some tea leaves or something and the tea leaves are okay but is that an idea that it's been around for 50 years is that is that is that still is that backed up by our latest geophysics i don't know but i wonder not a denier i'm not just uh and as i was just saying i i don't read geophysics papers about mantle dynamics in my spare time ed is iceland potentially developing into a celezia type terrain a large igneous province i don't think so ed it's an interesting thought we will after the quiz on thursday we will have a discussion of hot spots and my limited knowledge ties large igneous province to hot spots so i don't visualize large igneous provinces being created at a spreading ridge because we don't have obvious fragments of large igneous provinces all through the floor of the atlantic ocean for instance but again we barely have any of the atlantic ocean or the pacific ocean floor mapped talk about another final frontier i guess they're not final front talk about another frontier i think most of the ocean floors of the world have yet to be mapped accurately i thought we were the apex of civilization i thought it's all downhill from here i thought well no it's not the way to view it right these are the stone ages for a lot of things earth interior and bathymetric maps included okay a toast to you here's to your health here's to the health of your parents and your grandparents nick i i uh i need to remind you there are children watching it take this very seriously you are a professional representing the community so i uh admonish you for your behavior or i i would uh like to see a little bit more maturity out of you here's to all the hard-working people dealing with the global situation that we have continue to have we're hoping we're hoping here's to hope plate boundaries of the world that's coming tomorrow subduction and all sorts of other stuff and i'm a little worried we have more no-shows than than normal and if that continues to be the case i'm just going to put all my energy into the less than 20 people that we have in the room that's all i can do but you're still here that's a good thing thank you for tuning in have a good monday slash tuesday and we'll see you tomorrow morning at 10 o'clock goodbye i love you and goodbye and i love you and goodbye and furthermore i love you uh

Channel: Nick Zentner

Views: 16,071

Rating: 4.983211 out of 5

Keywords: Nick Zentner, sea floor spreading, Mid Atlantic Ridge, East Pacific Rise

Id: 7P41BfEwdTY

Length: 88min 39sec (5319 seconds)

Published: Mon Feb 01 2021