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Plate Tectonics Evolution
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0:00
I made a video a while back about how plate tectonics hasn't always involved plates on Earth there were tectonic regimes on Earth that didn't involve plates very very early on multiple billions of years ago but recently there was paper published suggesting that we should reinterpret the evolution of tectonics on Earth this new 20124 paper by Robert Stern has been published in the journal GSA bulletin and it challenged is our understanding of how long PL tectonics
0:33
has been operating on earth now when you hear the word tectonics especially with regards to Earth you probably imagine Earth's crust broken up into a bunch of plates that are shifting and colliding against each other and spreading and all these things that we talk about which is modern plate tectonics this is how tectonics works on Earth today and plate tectonics has shaped Earth's mountains ocean basins and even in large part climate and conditions for life but tectonics
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on Earth hasn't always involved plates like I mentioned earlier I have a video that I posted not too long ago that was actually an interview with Steven Balman a early Earth tectonic scientist we talked about essentially how tectonics hasn't always involved plates in that video and we talked about the evolution of plate tectonics and when it's thought that plate tectonics finally became the global regime on Earth as it is today and we talked about these major stages
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of tectonic regimes throughout Earth's history in that video starting with one the magma ocean stage so essentially very hot molten Earth of when it just formed and it's still solidifying and so it's just an A A magma ocean which is crazy cool but that was 4.5 billion years ago and it had just formed and then heat pipe Earth still very very hot Earth the crust is starting to solidify but
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it's still very volcanically active and hot and the mantle is still very hot and driving a lot of activity at the surface and the lithosphere and crust haven't really begun to become distinguished in the way that they are today I should mention that the lithosphere and the crust are two different things crust is the thinnest most outermost layer of Earth's material and it's very silicate Rich Which is less dense than the layers below it like the mantle and the core
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but the lithosphere includes both the uppermost mantle and the crust why do we designate a word for the lithosphere why don't we just go with crust mantle core it's because the lithosphere is actually what makes up the plates it's not just crust moving around on Earth surface that causes plate tonics it's actually crust as well as the uppermost part of the mantle that moves around and makes up earth's tectonic plates so why do we designate crust as being different than the
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lithosphere why don't we just call the lithosphere the crust because of density differences and compositional differences that I won't get into here but the gist is crust is the thinnest most outermost layer and the lithosphere includes both the uppermost part of the mantle and the crust and then the lithospheric plates the tectonic plates right along the asthenosphere which is more of a plastic part of the mantle that kind of convex and allows these tectonic plates to move around
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on Earth's surface that said at this point 4 billion years ago as we go through Earth time these lithospheric plates have not developed yet then we get to a tectonic regime on Earth around 4 to 2.5 billion years ago in the Aran Eon which we call some people call drip tectonics essentially the lithosphere has started to develop that's the green part here the purple is the crust and the lithosphere is undergoing deformation and tectonics where heat is being released at
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the surface and deforming the surface and stuff is going back into the mantle and recycling similar to how plate tectonics does today but not the same essentially the best way that I've had this explained to me by Steve in that previous video interview video is that plate tonics is more lateral and drip tectonics was likely more vertical so today we have these rigid lithospheric plates moving across our surface subducting and spreading from mid ocean ridges
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in a very lateral way it's laterally continuous with these rigid lithospheric plates whereas on early Earth pre-plate tectonic Earth in the Aran 4 billion to 2.5 billion years ago drift tectonics was driving tectonic activity where essentially the thing analogous to subduction on Earth today was this dripping which was much more vertical than subduction today and then we had upwelling and plumes like hot spot type vulcanism during this time as well but it wasn't necessarily you
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know subduction driven vulcanism that we see in a laterally continuous Regional way today and then finally starting around 2.5 billion years ago is thought to have been kind of the beginning of this transition to Global plate tectonics well I shouldn't say beginning of the transition it's thought that by 2.5 billion years ago so anywhere from 3 something 3.2 is to 2.5 billion years ago there was this transition from drip to plate tectonics and then around 2.5 billion
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years ago there was enough plate tectonics going on on Earth at that point that most geoscientists seem pretty comfortable to call that globally PL tectonics or Global PL tectonic regime which has continued until today and then in the far future future uh we will eventually have what's called stagnant lid tectonics where as Earth so throughout these regimes that we've gone over these past you know four regimes we've gone over of tectonics in Earth history these tectonic
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regime transitions have been caused by Earth cooling over time it was really really hot at the beginning it had magma ocean heat pipe tectonics and then finally crust started to cool lithosphere started to cool and it was drippy and really hot still and then it became more rigid and plate so as Earth has cooled it's led up to plate tectonics which will eventually lead into stagnant lid
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tectonics where essentially Earth is tectonically dead at the surface there's not enough heat from the interior driving surface tectonic activity or Surface heat release and then Earth will continue to cool until you know the sun explodes 5 billion years from now or whenever that's supposed to happen but and this is what we'll talk about in this video the new paper by Dr Stern in 2024 provides A New Perspective on this story I should mention also that this figure showing these
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tectonic transitions is also from a Stern paper he has led a lot of this Research into the tectonic history of Earth and so I believe this one's from originally Stern at all 2020 which I'll link below he also has a 2023 update and then this new 2024 paper which kind of provides A New Perspective a very incredibly interesting new perspective on the last 2.5 billion years so we're still keeping
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with the assumption that this you know this transitional history from 4.5 to 2.5 billion years is around the same as what we have talked about here obviously there's still a lot of research going into this but this is kind of the main hypothesis that we're going with right now and then he then provides a little bit New Perspective um and evidence behind some new ideas regarding the last 2.5 billion years of tectonic history so a little bit more recent essentially instead of
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just okay plate tectonics began 2.5 billion years ago and has been the thing that Earth has been going through the last 2.5 billion years to today Stern suggests that Earth has alternated between plate and lid tectonics over the past 2.5 billion years now when I say lid tectonics I don't mean stagnant lid like tectonically dead or inactive bodies like the moon or Mercury I mean active lid tectonics like what happens on mars or Venus which are both lid tectonics but different types
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of lid tectonics sluggish lid is kind of what he describes as slightly slower or less active mantle convection slightly less activity and and then the Venus scenario the squishy lid scenario is more activity but again lid tectonics meaning One Singular crust crustal you know shell of a planet or Moon you know body rather than a crust or shell broken up into plates so essentially the difference between these two he describes it as picture an eggshell now if you have an egg
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that has a shattered shell and there's different fragments or plates at the surface that's kind of you know where we get plate tectonics the idea of plate tectonics which is simple for us to imagine right CU we have grown up with this idea at least you know my generation has maybe not people older than me which we didn't know what was going on but we now know this is what goes on on Modern
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Earth the shattered eggshell picture but single Le tectonics is this unbroken eggshell that still allows for deformation and vulcanism but with no plates so he kind of shows a little diagram of this here it's similar to the drip tectonic regime kind of this vertically driven tectonic activity that doesn't involve rigid lithospheric plates now this might seem odd or unusual or kind of hard to imagine but it's actually more common than you might think actually plate tectonics is the
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weird child of the planetary family at least in our solar system so what's interesting and what I love about this so I should mention most of these images that I'm showing here are figures or at least parts of figures from his paper so I will link that below and you guys can check it out but essentially I love this figure because he showcases examples of each type of tectonic regime that you know we go through as we go through Earth's evolution of tectonics early on Earth we
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probably had a magma ocean similar to the asteroid Vesta then io's tectonic regime is likely similar to this heat pipe scenario on early hadan Earth four billion years ago when it was still very very hot just beginning to solidify at the surface and then Venus's tectonic scenario is this kind of lid tectonic scenario where you know it's just like what we just talked about one single eggshell unbroken but still able to deform and have activity at the surface upwelling and volcanism
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and downwelling that's more of an oceanic term but anyway down dripping of crestal and lithospheric material down into the mantle for recycling just in a more vertical way than plate tectonics and then I love that he puts this stage of plate tectonics here as optional because this is Earth this is where Earth is currently at in its stage of tectonic regime as it cools and it is kind of optional if we look at all the other planets and moons that are similar in composition that is
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mainly silicates so silicate minerals which you know Earth is a rocky silicate Planet uh as are these other planets and moons if we look at bodies like that we tend not to find plate tectonics we find lid tectonics like on Venus or Mars or you know dead lid tectonics like on the moon or IO we have this pre liid tectonic scenario but it will probably also go into lid tectonics it's very rare that we find that planets go into the plate tectonic regime I mean I say very rare we don't
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know of any other than Earth so at least not to my knowledge comment down below if we have found any maybe exoplanets that like I don't know I don't even think that we could detect that for an EXO Planet but Earth is a very unique scenario is what I'm trying to point out and I actually have a video on my channel where I talk about whether plate tectonics is required for life or vice versa
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which is an interesting concept because we talk about this possible link between plate tectonics and life that has been proposed for Earth and one of the major things that links them together is the necessity for water it turns out that there's a lot of people that think that water is one of the major things that drives plate tectonic motion and the physical capability of the lithos to break
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into plates and subduct and do all the plate tectonic things that it does on Earth is is this liquid water at the surface and this is really interesting because again liquid water being stable at the surface of any planetary body is a unique thing that we don't see very often and so Earth is again very unique for this so it could be that the stability of liquid water at her surface and it's kind of perfect goldilock scenario that it's in maybe gives it this unique ability ility
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to do the optional play tectonic stage before it goes to a slower lid tectonic regime and then to a stagnant lid tectonic regime so anyway Dr Stern is proposing that Earth has alternated between lid and plate tectonics throughout the past 2.5 billion years but before we get into the exact timing of the transitions that he's proposed in this paper you might wonder how exactly do we study ancient tectonic regimes what's the evidence that we can use to support different tectonic
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regimes in Earth's past compared to today well the rock record preserves what we call tectonic fingerprints that Trace tectonic regimes and episodes and transitions throughout our history just to name a few there are certain types of rocks like opoly sequences ultra- highpressure metamorphic rocks or blists that indicate plate tectonics these are rocks that or or sequences of rocks that we know can only form at least our under our current understanding can only form
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due to plate tectonic driven processes and then there are also rocks that we think form under lid tectonic scenarios or processes we think are associated with lid tectonics and you know we of course have ancient Earth to tell us about lid tectonics but also modern other planets that are currently in lid tectonics so you know ancient Earth isn't our only lid tectonic example you know we have Mars we have Venus and we can study we do a lot of studying of their geologic features and
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tectonic features at their surface to understand what ancient Earth might have looked like and what relics from ancient Earth from the rock record tell us about earth's tectonic history so using what are called PL tectonic indicators in rocks and single lid tectonic indicators in rocks Dr Stern was able to kind of put it timeline together of these Transitions and I should mention these
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fancy chemical data graphs that I'm showing at the bottom here aren't you know I'm not going to go through this all you don't have to understand this all I'm just putting it up on the screen because these are some examples of figures Dr Stern used in his paper and from other previous references as well he kind of pulled together a bunch of past literature as well as his findings to paint this
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picture and these are some examples of some of the figures he had showing the geochemistry of the record through time and what that indicates in terms of tectonic transitions so feel free it's going to be again linked down below feel free to dive into these figures further if you're interested so getting to the timeline now he identifies four episodes of tectonic transition from lid to plate and vice versa over the last 2.5 billion years starting with a single lid tectonic
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episode from around 2.4 to 2.2 billion years ago moving to PL tectonics from around 2.1 to 1.8 billion years ago then in the boring billion what we named the boring billion which goes from around 1.8 to8 billion years ago the boring billion we nicknamed it because it seemed like a pretty tectonically stable biologically stable chemically stable climatically stable period in Earth history
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that said I do have a video about it that kind of goes over caveats with regards to that nickname and what we've found since nickname naming it that that might hint at it being not so boring after all so please check out that video I'll link it to the top right if you're interested but anyway during this boring billion period we switched back from plate tectonics to lid tectonics and then
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finally we switched around 800 million years ago or8 billion years ago back to our current plate tectonic regime which has lasted since then note though when we talk about these transitions that there is probably .1 to2 billion years between each one of these that's 100 to 200 million years of time between these transitions so it's not like it was a flip of a switch these transitions took Millions hundreds of millions of years to transition if that makes sense it it's not like
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plate tectonics can go to lid tectonics and vice versa very quickly again tectonics is a very slow thing but it's possible that these transitions could have occurred over very long time scales okay so we have this new paper that says maybe play tectonics hasn't been the global regime for the last 2.5 billion years maybe there's been these transitions between plate and lid tectonics but why does this matter why do we care about this well understanding earth's tectonic history helps
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us decode our mantle processes today and what kind of activity might it drive at Earth surface today and in the future but it also helps us understand why our mantle is hotter than models predict PL tectonics is very efficient at cooling Earth's mantle because it brings down this cold dense oceanic crust and lithosphere from Earth's surface down into the mantle and again as we talked about
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in the timeline Earth has been cooling over time and the more that we cool its interior the closer we get to that stagnant lid tectonically dead body scenario but orus mantle is hotter than models would predict based on our understanding of tech tonic Evolution Through Time currently so maybe these episodes of single lid tectonics throughout the last 2.5 billion years slowed the cooling of
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the mantle enough to cause its current hotter than it should be state that said there are many many many ideas about tectonic Evolution throughout Earth's histories this is just one hypothesis so it's not you know necessarily the the only idea or way that we can get around this or or explain in this so you know that's an idea but another reason why we care about this and my particularly my
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favorite reason is that tectonics is closely tied to life as I talked about I have a video on my channel where I talk about the tie between are one of the major ties between play tectonics and life where I focus in that video on water but there are many other reasons that play tectonics is super important for life on Earth for example it supports biodiversity by creating diverse habitats and cycling nutrients the cyclic nature of plate tectonics Cycles nutrients through Earth's
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interior and transforms them back kind of recycles them back into stuff that life at the surface of Earth can utilize which is really really important it's actually one of the major things we look at for other planets whether they're tectonically active to decide whether they may be habitable because tectonically active bodies mean that that body has some sort of nutrient cycling scenario
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iio and and that can feed life it can literally feed life which is so cool it's thought that play tectonics specifically on Earth may have played a role in the evolution of complex life and it's possible that PL tectonics given its Rarity could help explain why intelligent life seems so elusive in our universe that said I don't want to make it sound like play tectonics is necessary for complex
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life it's not some sort of tectonic activity is really important to sustain life on a body however plate tectonic specifically is not necessarily required for life so yes we should still look for life on bodies that maybe don't have plates so anyway we care it it is very important that we understand the tectonic Evolution through Earth's history however not everyone agrees with this history that I've painted throughout this video and that Dr Stern talks about in his
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paper there are other hypotheses some for example argue that erosion subduction and metamorphism might have erased evidence of earlier PL tectonic activity meaning that PL tectonics may have started earlier than we think based on the Rock record because maybe the record has been erased or altered in some way whereas others think that tectonic Styles like lid and play tectonics might overlap to a certain degree rather than switch entirely so there's a lot
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of ongoing research in this realm of trying to understand tectonic Evolution through Earth's history and our planet's tectonic future if you want to learn more specifically within Dr Stern's paper I will link the full paper down below as well as other references that are primarily by Dr Stern in his lab group and I want to hear what you think about how have tectonics evolved through Earth's time do you think PL tectonics Rarity or apparent Rarity means anything for our
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search for alien life comment down below to let me know your thoughts and or any other papers that maybe I haven't seen on this that might also be interesting to cover on my channel and with that guys thank you so much for watching and I'll see you guys in my next one bye
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