Tectonics vs Plate Tectonics: Earth's Evolution Explained

[00:00:00]we've all known for at least a few decades that  Earth undergos something called plate tectonics   but what if I told you that tectonics doesn't  always involve plates that is plate tectonics   is not the only way that a planet or Moon can  undergo tectonic activity and even our own planet   earth has undergone different tectonic regimes  throughout its history it hasn't always undergone   plate tectonic so that is what we'll be talking  about in today's video the evolution of tectonics   on Earth the timeline of it what kinds of tectonic  regimes we think we're going on on early Earth and   all of that before I jump right into the video  this video is a little different than my normal   sit down and talk at you videos it is me sitting  down and talking at you but I have a special   guest because this is not my area of expertise I  invited on a fellow YouTube Creator and science   Communicator step Balman to talk about some of the  processes we think have gone on um tectonically   throughout Earth's history especially on early  Earth especially throughout the Aran 2.5 plus   billion years ago and he has so much more material  that goes so much more in depth on his channel so   at the end of the video I'll kind of shout out  some of the videos you can go check out on his   channel that will take you even deeper but thank  you so much Steve for coming on and talking about   this stuff you are just so brilliant within this  realm so thank you and we'll get started before we   jump right into tectonics and tectonic regimes  on Earth let me just kind of briefly introduce   the basics regarding tectonic plates currently  on Earth and kind of some definitions regarding   the layers of Earth so that you understand the  terminology as we go through the rest of the video   so first things first I do actually have a video  called something like tectonic plates versus crust   or vice versa uh these are not the same thing  as we can see on this picture it is not that   the green Parts the Continental land masses move  about the blue Parts the ocean um the oceans are   part of the plates continental and oceanic crust  make up the tectonic plates that we have on Earth   today why well it has to do with um kind of the  definitions of layers on Earth as I discussed in   that video the lithosphere is what makes up  earth's tectonic plates and the lithosphere   does not equal the crust it contains the crust  but it also contains the uppermost part of the   mantle essentially there are two ways that you  can Define layers of Earth and here's how Steve   puts it to clarify things there's two different  type of layers generally if you will of the earth   we have compositional and mechanical mechanical  layers are what tectonics and structural geology   we all deal with the compositional layers there's  three you basically have the crust the mantle and   the core and then you have two types of crust  continental and oceanic or felsic and maic but   mechanical layers you have the lithosphere now  the lithosphere for anyone who doesn't know is   the upper part of the mantle and on top of that  sits the crust and the crust is also part of the   lithosphere it's one of those annoying definitions  you kind of got to differentiate if you're talking   about like just the mantle part or the crust  part but these behave these are the plates the   lithosphere behaves the same you know the  lithosphere gets subducted with the crust   it's not just the crust going back in the mantle  it's that upper mantle as well the lithosphere   so it's a little thicker than just the crust so  mechanically when I talk about plate tectonics I'm   talking about mechanical I'm not really talking  about composition so this is why some lithospheric   plates contain both continental and oceanic  crust it's because the lithosphere is really that   uppermost part of the mantle and whatever crust  lies on top of that not just the crust therefore   it's broken up differently than the boundaries  of continent to Ocean so now that we know the   lithosphere is the layer of Earth we're talking  about when it comes to plate tectonics what   exactly is plate tectonics well first let's define  tectonics the definition of tectonics I just have   the deformation of a planet's lithosphere  caused by plan Planet losing its internal   heat and that drives every terrestrial planet's  tectonic system it's just how does that body get   rid of its internal heat that's really all it is  but what makes tectonics plate tectonics when do   we call it plate tectonics well Steve says it's  as simple as it must involve plates so what are   tectonic plates how do we Define these well Steve  says and then we have the definition of a plate   physically separated segments of the lithosphere  with well- defined physical boundaries for example   spreading ridges subducting subducting trenches  and transform contacts you know spreading centers   uh convergent margins you know that kind of stuff  you know a lot of people think subduction equals   evidence of subduction equals evidence of PL  tectonics or evidence of crustal recycling   thus for plate tectonics and that's couldn't be  further from the truth to have plate tectonics   you have to have plates you don't have plates  you don't have plate tectonics so essentially   as Steve mentioned tectonic plates have to have  well-defined boundaries boundaries where they're   pushing together causing what we call Convergence  zones on Earth um where you know if it's an ocean   continent Convergence Zone the oceanic plate or  the lithospheric plate containing oceanic crust   subducts underneath the one containing continental  crust crust just because the continental crust   containing lithospheric plate is more buoyant  we'll get to why that is later on um and this   creates what are called subduction zones as he  importantly mentioned subduction zones are not   evidence for plate tectonics because we do have  regimes in Earth's really early history that may   point to subduction without the need for plate  tectonics and I'll get to that later as well and   then also some other well-defined plate boundaries  are things like mid ocean ridges where plates are   pulling apart causing new ocean crust to form or  Continental Rift zones where the same thing is   happening but in a continental crust containing  lithospheric plate um and also the third type or   the third major type of plate boundary is uh  transform plate boundaries where plates slide   against each other so push together pull apart  and slide against each other are the three kinds   of plate boundaries that Define tectonic plates  on Earth Earth so we have tectonics which is how   a planet in this case Earth loses its internal  heat and we know that plates are required for   plate tectonics and we talked about how plates  are physical segments of the lithosphere with   well- defined boundaries so do we have a good  definition of plate tectonics overall well here's   what Steve says plate tectonics is a tectonic  theory that explains the formation of geologic   features caused by how a planet loses its internal  heat and the reason why I have tectonic theory is   because a lot of people think plate tectonics is  just continental drift and it's not continental   drift just says the continents move about the  globe that's really all it says but a lot of   people think the continents sit on the ocean floor  and slide around yeah and that's not it continents   are part of these plates the planet is divided  into rigid plates with well delineated boundaries   he also goes want to point out the lateral nature  or kind of horizontal or side to side nature of   plate tectonics compared to other tectonic  regimes but we'll talk more about this later   and how other tectonic regimes in Earth's history  have been more vertical compared to lateral like   plate tectonics and how these different tectonic  regimes and their more vertical nature affected   the geological features forming at that time but  Steve also made sure to stop before we moved on   to discuss what drives plate tectonics because we  can't have a good Theory without talking about and   understanding the mechanisms behind it so what  does Drive plate tectonics these are the three   dominant mechanisms that we suspect happen slab  pole which is at convergent boundary subduction   zones mantle convection happens in the interior  the Earth and that's the one everyone's familiar   with that's the one you see in National Geographic  and all that stuff of this churning mantle like   it's liquid the mantle is a solid most people  don't realize that it's just uh any solid will   experience three General deformational experiences  elastic which means it pops back to where it was   you ever lift something heavy and it hurts your  arms that's because you're in that elastic limit   you better stop what you're doing plastic which  is a permanent state of deformation once it's in   that stage it can't go back elastic but eventually  you ultimately get to brittle failure and it just   snaps and that's what gives faults the reason why  we don't get earthquakes deep into the mantle is   because the mantle is plastic it's in that state  of plasticity constant and it's plastic regime if   you will is very large compared to any sort of  brittle or elastic deoration we used to think   that was the driving force and even my tectonics  book kind of says that well out in the 1970s there   was a couple of papers that came out about slab  pull and we knew subduction happened then we just   didn't think this was a thing really affecting  plate tectonics well we can well first of all we   can discount Ridge push Ridge push is not powerful  enough those are shallow magmas you can melt rock   not only by heating it but also adding water and  releasing pressure that lowers that melting curve   and that's essentially what's going on at the mid  ocean ridges so that's not powerful enough by any   means to get this system going we know that  we've always known that so it's between man   convection and slab pole we think slab pull like  said is a concept from the 70s that as these ocean   plates get old and less buoyant and thicker that  eventually they experience brittle failure you get   faulting and then gravity takes over gravity  driven system and that starts to subduct that   well inste of place are rigid something's got to  happen somewhere else you can't just so it's going   to experience br that formation somewhere else  we think at slab pole is the number one mantle   convection is number two and ridge push is kind  of just like a side effect of this gravity-driven   system so now we know what plate tectonics is  what the plates are made of how they move and   what drives their movement but play tectonics  is only one tectonic regime as we talked about   at the beginning of the video it turns out that  Earth has not always undergone plate tectonics so   when did plate tectonics begin on Earth and how do  we know that it was not operating on early Earth   2.5 billion years is pretty much the beginning of  when we start to see really good passive margin   sequences and things that are purely signs of  tectonics modern tectonics there seems to be a   transition zone but it breaks down before 2 and  a half billion years you start to see things in   the Rock record geology structures that don't  exist today you see things that aren't part of   the modern tectonic regime and that's one of  the biggest points well was play tectonics in   operation the whole time or not this is the Katon  stable platform North America now but this wasn't   always Katon kraton's gotten larger over time  as as the continent and parts have broken off   and sailed away but this is mostly Mesozoic  tertiary deposits and this looked a lot like   this until the Rockies formed but we're going to  leave that aside we're going to look here you come   here okay Gulf of Mexico for reference Florida  we come up and here you see the Illinois Basin   East interior Basin this is all Paleozoic mostly  and you see how this just looks you don't even   need to know anything about this you just look at  this and you see how these units are arranged on   the map now all fanner Oak just like the stuff to  the left here and we're not going to talk about   the Appalachians because that's a very complex  geologic history we're going to screw up and   now you get to my area the Upper Peninsula here's  Minnesota for you and here's Ontario and you get   up here and looks looks completely different and  then you get back to furoic deposits up in Hudson   Bay Area James Bay Area and you see these pink  Parts which are granitoids and then you see these   green Parts which are kind of greenstones for the  most part and these these are all greenstone belts   they have different names they're all pre camri  and most of them are Kean well pretty much all   of them are I think there's a couple that might  not be there might be a l younger but this regime   yeah it's been deformed yeah there's vaults  but this looks like nothing anywhere else I   mean even if you go to you know the Rockies in  the Appalachians it doesn't look like this and   that's really bizarre because basically what  we had is we have assembl of greenstone belts   which are basically mic lavas with thin set on  top very thin nothing like we even see in the   Paleo or in the protozoic at all so from all  of this Steve says that we know that something   different was going on on early Earth before about  2.5 billion years ago something that wasn't plate   tectonics but what exactly it was is still up for  interpretation but we have some ideas essentially   there is a general sequence of tectonic regimes  we think have evolved over time through Earth's   history and will continue to evolve and we'll  talk about this in a second the first tectonic   regime that we think was occurring you know very  early on Earth just after formation was a magma   ocean regime which is just what it sounds like  essentially you have the mantle and then a magma   ocean at Earth's surface because Earth was so hot  um and this magma ocean was not yet yet Cooling   and forming Hard Solid rigid crust uh like we have  today just yet and then in the late hadian nearing   4ish billion years ago we're not exactly sure on  the timeline of this these are very fuzzy numbers   especially the further we go back in Earth's  history but we think nearing the late hatian   nearing 4 billion years ago moving into the Aran  which went from around 4 to 2.5 billion years ago   we had heat pipe tectonic essentially the type  of tectonic regime we think is currently going   on on iO the volcanic moon of Jupiter and this is  a scenario in which Steve says essentially there's   crust um and then a partial melt of the upper  mantle but no upper manle lithosphere like we   have today so the green you can see in the later  diagrams are representing the lithosphere or at   least the lithospheric mantle the uppermost part  of the mantle we said was part of the lithosphere   as is the crust but in this heat pipe scenario  there is a crust but no manol lithosphere and   then we get into the regime the tectonic regime  where things start to get really interesting and   this is called drips and plumes this is what the  Aran in North America looks like where you just   have a simple ocean crust or crust we'll just say  crust and it's mic and then you get these felsic   bodies intruding these granitoid which actually  deform and push down this ocean floor CU like I   said it has sediments on it but they're very thin  sediments there nothing like today so whatever was   sourcing that sediment was probably little tiny  High areas on the ocean floor but true continents   I don't know like people have postulated super  continents or Continental bodies back into the   deep Aran but those all need to be taken with a  grain of salt but BAS basically what'll happen   is you get this mantle convection and this would  be a mantle driven system so that leads to things   moving and colliding and instead of subduction  what you get is this pull down and this pull   down this drip if you will starts to pull that  maic rock back into the mantle and then since   you still have a hot mantle which at the time is  about 200 degrees C hotter than it is now so even   if we did have plates subducting into the mantle  then they got very deep because the mantle is a   lot hotter they would have been reincorporated  relatively shallow so essentially one really   important distinction between this drip tectonic  regime and the current plant tectonic regime that   Steve emphasizes is that plate tectonics again  is the lateral movement of lithospheric plates   across you know the surface of Earth due to  the mantle convection and slap pull whereas   the drip tectonics was more of a vertical process  of the dripping down of crust back into the mantle   kind of like subduction but vertically instead of  laterally and the plumes of you know kind of like   hot spots today like we have Hawaii Yellowstone  essentially lying over hot parts of the mantle   that drive plumes of you know material to rise  and cause volcanism at the surface just a much   more vertical process than large scale plate  tectonics is today and also seemingly driven   a lot more strongly by mantle convection than  obviously slab pole is today because slab pole   drives the lateral movement of plate tectonics  through gravity and this drip tectonic regime   is thought to have continued on throughout the  Aran Eon and then well we'll talk about the exact   timing of the transition to Modern styop plate  tectonics later but it's thought that around 2.5   billion years ago is when full you know modern  style plate tectonics might have finally been   the global Norm um but this transition was very  slow and not globally instantaneous and we'll   talk later about when we think the transition  occurred and how Earth might have looked like   in the dript plate tectonic transition period  which was a long period and then finally we have   the you know final tectonic regime of Earth which  which is just going to be a terminal stagnant lid   essentially no tectonic activity and that will be  you know far future earth when it has finally lost   all its heat so what did Earth look like during  this pre-plate drip tectonic period in the Aran   from around 2.5 to 4 billion years ago and when  did continental crust differentiate from oceanic   crust so again going back to what we talked about  in the first part of the video there are are two   types of crust on Earth the blue parts and the  green parts and essentially this is ocean and   continental crust and obviously you know from this  view we could just say oh well the ocean is blue   cuz it's covered in water but the crust underlying  the ocean and the crust that makes up continental   crust that makes up land that we live on these two  crusts are very different in composition and they   underw tectonic processes that caused them to  differentiate to become you know either oceanic   crust or continental crust and their compositional  differences lead to behavioral differences there's   a reason that ocean crust always subducts under  continental crust oceanic crust forms at mid ocean   ridges and is mic and thus thinner and denser  than continental crust and so it subducts under   Neath continental crust which is thicker and  more buoyant than oceanic crust and it forms   at subduction zones and is felsic maic and felsic  are just terms relating to the composition of the   crust um mic means it's relatively more silica  poor silicon and oxygen poor uh whereas felsic   contains a lot more silica or silicon and  oxygen essentially you don't really need to   know what that means other than the fact that more  felsic material is more buoyant is is less dense   and more maic material is more dense that's why  oceanic crust can subduct and continental crust   does not subduct but if continental crust forms  at subduction zones does this mean that there   were no continents before plate tectonics well  Steve says there is evidence for the formation   of some early felsic crustal material around 3.8  billion years ago long before plate tectonics was   the global regime moreover many studies suggest  that much of the continental crust potentially a   majority of the continental crust that is around  today formed during the Aran before 2.5 billion   years ago before plate tectonics was the global  regime so how is this the case if continental   crust formation necessitates subduction well  remember that Steve said subduction does not   mean plate tectonic subduction can occur in other  tectonic regimes it's just not exactly the same   thing when we think about the way that plates  subduct which is a very lateral and rigid system   so essentially it is possible that drip tectonics  or some sort of drip to Plate transitional Global   tectonic regime could have led to the formation of  the first very early pods or small land masses of   continental crust before plate tectonics was the  global regime I had previously shown this figure   in that video that I mentioned that was you know  tectonic plates versus crust explaining how early   continental crust differentiated from oceanic  crust during the arcan Eon however as you see   here this is clearly a plate tectonic regime and  I now know and probably the people that made this   figure now know that it was probably more likely a  drip or drip plate transition tectonic regime than   this rigid Global plate tectonic type of system  and it's important to note when we're thinking   about this that the reason subduction drives the  formation of continental crust and also the reason   that we originally thought that it necessitated  plate tectonics is because subduction drives what   we call partial melting which is exactly what it  sounds like of magma which leads to the formation   of more felsic material felsic continent crust why  because if you take a bunch of rock that has both   felsic and maic material in it and you melt it  felsic material melts at lower temperatures than   mic material therefore if you take a lithospheric  plate that contains oceanic crust and you subduct   it into the mantle and it begins to melt the  first thing that's going to melt out of that   crust is the more felsic components and because  these materials melt out they rise they form melts   and hot material in the mantle Rises Rises through  the lithosphere Rises you know up to the crust and   it causes volcanism at these subduction boundaries  and this volcanism is releasing Fick material cuz   that's the stuff that melted out you're never  going to get a melt that melts evenly and all at   once and releases all the material to the surface  it's always going to start with the stuff that   melts at the lowest temperature because that's  what it reaches first the temperature rises as   it sinks through the mantle and it when it hits  the very first temperature that is required for   any of that material to melt that material leaves  the system goes to the surface and leads to the   formation of felsic you know at the time on early  Earth PODS of continental crust not this Big Slab   here obviously this picture of is of modern  Earth but you know you get the picture and so   that's why we originally thought that plate  tectonic specifically subduction zones were   required for the formation of early continental  crust however again like I mentioned earlier we   now know and think that it's possible that some  subduction like processes were occurring during   the drip tectonic regime as well as the dript  plate transition tectonic regime that we think   could have driven the formation of the first  Continental pods or PODS of continental crust   or land so back to our original questions I asked  I don't know how many slides ago what did Earth   look like during the pre-plate drip tectonic  period in the Aran and wind did continental   crust differentiate from oceanic crust well Steve  says it was likely an ocean dominated world with   some maybe Hawaii like Islands here and there that  popped up due to the more Hots spot-like drip and   plume tectonic driven vulcanism going on during  this time time again think more vertical and like   individual isolated spots rather than horizontal  strings of mountain building and whatnot like we   have today and then as things shifted from drip  to plate tectonics more Continental pods began to   form and then finally as plate tectonics became  the more globally continuous regime these pods   began to collide because subduction between them  would you know eventually allow them to meet and   form larger land masses and again that happened  over and over again until they could accrete into   very large land masses that formed early cratons  that we now have you know underneath a lot of our   Continental land masses today so when exactly did  this transition from drip to plate tectonics fully   occur well Steve says that it was probably about  3.2 to 2.5 billion was a transition and then we   got something resembling what we would recognize  today now obviously there was still you know over   time the lithosphere is getting thicker it  didn't just get thicker overnight at 2 and   a half billion and start driving BL tectonics so  again he emphasizes that this transition was not   at all instantaneous it marks a period of about  700 million years so it happened very slowly and   heterogeneously across the globe it wasn't like  one day it was drip and one day it was plate it   was probably drip is in some areas and plish in  some areas but not continuous and he even says   that hot spot volcanism today things like Hawaii  Yellowstone vulcanism driven by hot spots in the   mantle rather than large scale plate tectonics  might be relics of this more drip likee tectonic   regime he even said that hotspots will likely go  extinct in the coming year I mean not soon but   will probably cease to exist in Earth's future  before plate tectonics comes to an end and then   eventually again again like the diagram showed  earlier will come to a stagnant lid tectonic   regime essentially no tectonics once Earth has  lost all its heat so the take home message from   my conversation with Steve which by the way  was like 3 hours long I had to cut it quite   down because it was you know we are geologists  we get to talking um but the Takeo message is   that not all tectonically active bodies have play  tectonics this not only applies to early Earth   but also other planets and moons like for example  Europa IO Enceladus and other moons of Saturn and   Jupiter Europa for example is a moon of Jupiter  that has an ice covered liquid water ocean just   like Enceladus and we think that these moons  well we don't think we know they're tonically   active I mean look at the surface of Europa we  can see tectonic features and we also see plumes   literally jetting out of enceladus's South Pole  constantly so we know there's tectonic activity   obviously they are losing heat in some way we  also see on iO the volcanic moon of Jupiter   the most volcanically active body in our solar  system the obvious loss of heat through vulcanism   going on and so it is also tectonically active  but these moons don't have plate tectonics why   is this an important distinction well we have  to be careful when interpreting their surface   tectonic features because their tectonic regimes  are different than our own modern plate tectonic   regime and typically our first go-to response to  seeing any feature on another planet or moon is   relating it to something we see on Earth which is  a good first goby but obviously cannot be made as   a direct comparison likewise since moons like  Europa IO Enceladus and other moons of Saturn   and Jupiter are heated by tital stretching the  gravitational pole and stretch driven by the h   huge gravity of Jupiter and Saturn rather than  driven by internal heat like Earth this might   heavily affect the way that heat is dissipated  through their bodies and the way that obviously   tectonics operates on these types of bodies and  also with that comes differences in composition   and size and gravity and orbit and so many other  things that are probably affecting their tectonic   regimes and the way that tectonics operates  on them but overall you know that is to say   it's important for us to understand the history  of tectonics on Earth and what that might have   looked like so that we can interpret um these  other worlds and kind of the stage of tectonics   they might be in as well as how it might progress  in the future so I hope you guys enjoyed learning   about the difference between plate tectonics  and tectonics today as well as hearing from our   fellow YouTube geologist Steve Balman thank you so  much for being on again and if you want to see see   more of his stuff I swear he's got like hourlong  amazing lectures where he draws like diagrams and   stuff of the things I was trying to explain but  probably not properly um and so if you want to   check out those go I will link a video up here  I'm sorry if you hear crinkling right now it's   because my cat is licking a plastic bag it's just  something she likes to do I don't know don't worry   she doesn't eat it anyway so check out Steve's  video and I will see you guys in my next one bye