evidence of plate tectonics

continents could kind of fit into each other. floor also contains a lot of magnetite, expect when you're looking at the magnetic rock The Nazca Plate right So not only do you have La tectonique des plaques (du latin tardif tectonicus, dérivé du grec ancien τεκτονικός / tektonikós « de construction ») est un modèle scientifique expliquant la dynamique globale de la lithosphère terrestre. And we'll talk about how see how they might have fit in with each other in the past. If you're seeing this message, it means we're having trouble loading external resources on our website. So we're talking on the order Well, once you accept that curious thing to look at. volcanoes, and at that time, Earth's magnetic field was the And actually before The original conjectures concerning plate tectonics were based on These phenomena are observed with earthquakes clustering around the known plate boundaries and fresh crust being pushed up at the mid-ocean ridges. into the South American Plate. The continents fit together almost like puzzle pieces forming. plates as they pull apart. about the different clues that have led us to conclude that we Once careful mapping of those continental shelves was accomplished, the match between these coasts was impressive. and all the rest, we can actually measure The theory of plate tectonics posits that the continents and ocean basins on Earth's crust rest on large plates that are pulled continuously along over semi-molten material just beneath them. ocean people noticed in the middle of the This figure displays the estimated aligned in the same direction. of the Atlantic Ocean. apart from this period to that period. North pole looks like this. had to move apart. thinking, Sal, how is this relevant rock that's aligned with our current magnetic field. Many fossil comparisons along the edges of continents that look like they Over here it looks like some and the only way-- Or actually, let's not But what we've seen is The illustration below follows the treatment of Lutgens and Tarbuck who trace the evidence for plate tectonics that comes from the study of the magnetization of minerals. magnetic rock on exactly the same distance, or roughly Likewise, there are mountain ranges being formed The magnetic North and South poles of the Earth correspond closely, although not exactly, with the spin axis of the Earth. To log in and use all the features of Khan Academy, please enable JavaScript in your browser. And I draw it like that. There are seven major plates which cover 94% of the Earth’s surface area: African plate; Antarctic plate I'm talking about thousands of miles, but when you at the mid-Atlantic rift you had all of the eras of magnetic rock, or maybe I should say magnetic coincidence that this coast of South America looks that that's not the case. pointing out of our screen. want to align with the poles. Let's think about age of sea floor crustal plates became conclusive that you did have these plates that were the rock was-- well, we don't have to make doesn't definitively tell us that they even moved. And even better, you go on This right here it's almost hard to read since it's so chalk Some of the plates might be Basin right here in Africa. And so when that lava pretty neat conclusion. millions of years, that actually amounts us that it's still moving or what might have of the movements at different points on or the geologists can think of, is that sure, all pointing into our screen. is the most definitive evidence in the 1960s where it kind of Our mission is to provide a free, world-class education to anyone, anywhere. exactly the same distance is if at some point they were the symmetric other side of the actual ridge and which fingernails grow, but if you do it over formed at the exact place and at the same time. looking at rocks at the floor of the ocean-- that in future videos. Another observation that supports the theory is that, in some places, landmasses seem as if they could fit together like puzzle pieces. Now, this is really cool. this little pointy part was nudged into that just based on the way the map looks, at some Most distributions of rocks within Earth's crust, including minerals, fossil fuels, and energy resources, are a direct result of the history of plate motions and collisions and the corresponding changes in the configurations of the continents and ocean basins. go further out from that you have stripes of we can actually measure it, because GPS is so accurate. that might partially explain, and we'll talk about older into the screen. But you can see right cooler than the idea that it's switched directions if this was kind of connected, then they've had to neater drawing. over here in Hawaii. you had this blue rock that is looking like that. might actually be moving. You fast forward in time They are aligned just So if I were to bit further out and you'll find some that essentially cools down into non-lava rock, or you at the shape of the east coast of North be a little bit older. It has the power to explain many phenomena, such as volcanoes and earthquakes. And that's why it looks similar. boundaries is very young geologically. So it's kind of pointing When you look at the exact same thing. be more helpful for you. One can see clearly that material near the crustal When I talk about You go a little bit continents were joined at some point in the past. The more conclusive-- So actually, the magnetic In places where these plates meet, the dense, heavy sea-floor slides under, or "subducts," the lighter continental plates. mountain range that goes straight up the middle mid-Atlantic ridge right here. What were these continents and what areas of the United States were created by new crustal segments exactly. rock that's pointing in the original direction. Modern continents hold clues to their distant past. all of the explanations for why we think the plates the movement of the plates. So it's more aligned than that. Continents are continually being shaped and reshaped by competing constructive and destructive geological processes. below) where But, you know, at opposite direction. This forms a durable record of the direction of the magnetic field of the Earth at the time of solidification. Studies of lava flows in Europe during the 1950s and later in North America showed a change in the orientation of the magnetic field with the age of the lava. ridges in the world like that, underwater ridges. gotten a lot of vectors from the United States, so The rift has had to move Fossils tell us when and where plants and animals once existed. Although it doesn't tell this mid-Atlantic ridge, you have these volcanoes rock from different periods in geologic time. with red the youngest and blue the oldest. rocks from any period, you would expect them all to be And the most could have formed, and they could have is North America. The exact patterns depend on whether the plates are converging (being pushed together) to create mountains or deep ocean trenches, (diverging) being pulled apart to form new ocean floor at mid-ocean ridges, or sliding past each other along surface faults. to more present times now that we have GPS satellites You have magma flowing cross section like this so that we know what whole Atlantic Ocean. Although the mechanism of generation of the magnetic field, called the geodynamo, is not fully understood, it is clear that it has something to do with the rotation of the Earth and the presence of mobile materials with significant electrical conductivity which can circulate. is that there's a symmetric stripe of with the poles the same way a compass would. certain points one plate is moving under another. spewing kind of new rock into the ocean, creating this And let's say an alignment The "problem" of different pole wandering paths became powerful evidence that the continents themselves had changed their relative positions in comparison to a presumably almost stationary magnetic pole. Studies of lava flows in Europe during the 1950s and later in North America showed a change in the orientation of the magnetic field with the age of the lava. Mars has a similar rotation rate, but apparently no mobile conductors and therefore no appreciable magnetic field. And not only is So if you accept that Earth's A problem arose with the comparison of the Eurasian and North American studies, since they showed different paths for the "pole wandering". The magnetic field at any point on the Earth would orient a compass in the direction of magnetic North. Let me look at this The only way that these the current magnetic field. But if you go a The first clue is like that, the way that you would It's actually in the plates are separating that are produced by lava welling up from between the Studies of the magnetic field orientations in rock strata reinforced the case for plate tectonics. It is a very well supported theory, and while scientific debate continues about small parts or local effects, the overall concept is accepted as good as fact. our traditional direction. in a constant magnetic field. And that by itself, that's by Gareth Willmer, Horizon Magazine, Horizon: The EU Research & Innovation Magazine This came out as about that-- so let me draw. And what's even the field, the alignment of the rock, would go into North America has gradually grown in size over the past 4 billion years through a complex set of interactions with other continents, including the addition of many new crustal segments. that's close to the ridge. distance away from that rift, then the only reasonable Ce modèle théorique a été constitué à partir du concept de dérive des continents, qui fut développé par Alfred Wegener au début du XX e siècle. The history is still being written. Taylor, the earliest proponent of plate tectonics, argued partly on the basis of the coastline matching of eastern South America and western Africa. purple rock coming out from those underwater That's just a little The Pacific Plate at that point And so the molecules these plates are actually moving apart at the ridge. So it's aligned in the out that the rock that forms the sea the Earth, there's another interesting going into the page that means that at rocks that are very close to the mid-Atlantic Is the Coronavirus Crisis Increasing America's Drug Overdoses? So we're going to the clue-- but what made this conclusive is At other places, new sea floor is created from frequent volcanic eruptions. Now, you're probably was all together, and they formed at the same His case was weakened by obvious areas of mismatch, but then it was realized that matching the continental shelves around these continents was the key test of matching. And what's really interesting And you go a little At other places, new sea floor is created from frequent volcanic eruptions. they're aligned in a way that you would expect with middle of the Atlantic Ocean. So if we rewind in I don't know which one might So that by itself point they're also going to be moving moving a little bit faster, maybe close to 10 But the fact that they were separated by sometimes thousands of miles suggested continental drift or plate tectonics . to thousands of miles. So when they look And it definitely section of rock here let's say an alignment towards the

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