Tectônica de placa Descobrimos como construir uma bomba atômica antes de percebermos como as montanha

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Tectônica de placa: Descobrimos como construir uma bomba
atômica antes de percebermos como as montanhas se formam
Cerca de 50 anos atrás, os pesquisadores descobriram um vazamento nos oceanos da Terra. A julgar pela química
do vazamento, parecia estar vindo do manto. Essa percepção aparentemente pequena é realmente enorme.
Se o vazamento estivesse ligado ao manto, isso significaria que o fundo do ser do fundo do ser espalhado de
alguma forma, para abrir caminho para o material do manto emergir. Se o fundo do fundo do fundo do fundo do
fundo do fundo está se espalhando em alguns lugares, então ele está empurrando o material – e do outro lado do
planeta, outras partes do solo são esmagadas juntas.
Em termos mais geológicos, se você tiver um limite divergente (onde o solo é empurrado para pedaços), você
também deve ter um limite convergente (onde o solo é empurrado juntos).
Fica ainda mais interessante: uma vez que a propagação do fundo do fundo do fundo do fundo do oceano parece
estar acontecendo em mais de um lugar, então isso significa que existem múltiplos limites, tanto divergentes quanto
convergentes. Se este for o caso, então a superfície da Terra não é uniforme, mas sim dividida em placas diferentes.
Agora chamamos essas placas de “placas tectônicas”, e a teoria por trás de como tudo isso funciona é chamada de
“tectônicas placas”.
A tectônica de placas transformou nossa compreensão das características físicas da Terra e sua evolução. Ele
afirma que o movimento dessas placas é impulsionado pelo calor profundo dentro do manto da Terra, e as placas
deslizam, se afastam e colidem umas com as outras.
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https://www.sciencenews.org/article/earth-oceans-tectonic-plate-mantle
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https://www.zmescience.com/science/seabed-map-23423/
https://www.zmescience.com/science/geology/tectonic-plate-portugal-08052019/
https://pubs.geoscienceworld.org/sepm/books/book/1076/chapter-abstract/10545894/Plate-Tectonics-And-Sedimentation?redirectedFrom=fulltext
https://www.zmescience.com/science/physics/part-of-earths-mantle-is-shown-to-be-conductive-under-high-pressures-and-temperatures/
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Uma renderização do fundo do mar espalhando-se
provocando vazamentos nos oceanos.
O movimento da placa tectônica é lento, mas implacável. Como uma aproximação, as placas se movem
aproximadamente na mesma velocidade que suas unhas crescem. Mas esse movimento lento é responsável por
praticamente todas as características geológicas que vemos hoje – das cadeias montanhosas às fendas do mar
profundo. Antes das placas tectônicas, nos faltava uma boa compreensão de como as montanhas se formam e
terremotos ocorrem.
Antes do nascimento da teoria da tectônica de placas, estudar a geologia era essencialmente um
exercício de coleta (aparentemente díspare) fatos e memorizar informações. A geologia estrutural estava
preocupada com descrições e compreensão da deformação por si só”, escreve o especialista Yong-Fei
Zheng em um artigo descrevendo o quão impactante a tectônica de placas tem sido.
Definição de tectônica de placa
É difícil resumir uma teoria tão complexa em termos simples e acessíveis. Mas aqui vai.
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https://www.zmescience.com/science/ai-deep-sea-research-8072536/
https://academic.oup.com/nsr/article/5/2/119/4913787
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Um modelo das placas tectônicas da Terra. Créditos da imagem: Museu Americano de História Natural / Tom
Magliery.
A camada mais externa da Terra, que se estende até cerca de 160 quilômetros de profundidade, consiste em
aproximadamente 15 placas de rocha rígidas e robustas. Essas placas, semelhantes a blocos de gelo em um rio,
mudam em relação umas às outras. Chamamos essa camada de litosfera.
Abaixo dessas placas encontra-se uma camada de rocha conhecida como astenosfera, que está perto de seu ponto
de fusão e serve como camada deslizante para placas tectônicas. A maior parte da deformação da Terra, juntamente
com a ocorrência de terremotos e vulcões, ocorre nos limites dessas placas.
Esses limites são locais de movimento divergente, como ao longo do Mid-Atlantic Ridge; movimento convergente,
como visto em arcos de ilhas e trincheiras do fundo do mar, como o Japão; ou deslizamento lateral, como observado
ao longo da falha de San Andreas da Califórnia.
O conceito de placas tectônicas não é apenas uma teoria sobre a estrutura da Terra; é uma estrutura unificada para
a compreensão da geologia da Terra. Ele explica a localização de terremotos, vulcões, cadeias de montanhas e
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outros fenômenos geológicos. Ele também fornece uma base para a compreensão do passado da Terra, como a
existência de supercontinentes como Pangeia e o desenvolvimento dos continentes distintos do planeta.
Apenas alguns dos processos tectônicos associados às placas tectônicas. Imagem via Wiki Commons.
Movimento da placa tectônica
Os vazamentos do fundo do mar não foram o momento “eureka” para a tectônica de placas. Na verdade, não houve
um único momento ‘eureka’ com tectônica de placas. A tectônica de placas é uma teoria unificadora, então você
precisa de vários tipos de evidências.
Grande parte dessa evidência é extremamente complexa. Mas algumas delas são muito simples. Tão simples, de
fato, que uma criança poderia fazer uma observação sobre isso. Basicamente, alguns continentes parecem caber
como peças de quebra-cabeça. Mais notavelmente, América do Sul e África.
Continente em forma. Imagem via Wiki Commons.
É verdade que isso pode ser uma coincidência ou explicado talvez por outra coisa. Mas os pesquisadores apoiaram
isso mostrando que fósseis semelhantes foram encontrados no leste da América do Sul e na África Ocidental. Esses
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continentes realmente pareciam ter ficado juntos em algum momento. Chamamos agora essas estruturas antigas,
quando dois ou mais dos continentes de hoje se uniram, “supercontinentes”. Alguns exemplos são Pangaea e
Gondwana.
Mas as aberturas e o ataque dos continentes não foram suficientes para convencer os geólogos.
Terremotos e montanhas como evidência
Todas as placas tectônicas são alimentadas por correntes no manto.
Outra evidência importante veio de terremotos. Para começar, há muitos terremotos (e vulcões) em lugares onde
haveria bordas tectônicas. Há o notável Anel de Fogo, mas outras bordas também.
Earthquakes also carry with them information. Researchers analyze seismic waves that come from earthquakes to
get information about the structure of the Earth. Did you ever wonder how we know so much about the Earth’s mantle
and core, for instance, which are hundreds or thousands of kilometers deep, when the deepest hole we’ve dug is
about 12 km? It’s mostly seismic waves.
Through seismic waves, geophysicists managed to confirm the proposed structure of the Earth, including the
lithosphere and the asthenosphere. They also managed to confirm some of the properties of the mantle (and the
crust) that would enable plate tectonics to function.
The boundaries where tectonics spread and collide also confirmed this theory. If crustal plates spread in areas like
the mid-Atlantic ridge, then the seafloor around these ridges would be very young. Furthermore, it would be youngest
at the center (where matter from the mantle constantly pushes up), and older towards the edges. This is exactly the
case.
https://www.zmescience.com/science/geology/what-is-gondwana/
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https://www.zmescience.com/feature-post/natural-sciences/geology-and-paleontology/planet-earth/what-is-the-ring-of-fire/
https://www.zmescience.com/science/geology/earth-mantle-hotter-06032017/
https://www.zmescience.com/science/geology/the-types-of-seismic-waves/
https://www.zmescience.com/science/news-science/earth-core-solid-19102018/
https://www.zmescience.com/feature-post/natural-sciences/geology-and-paleontology/planet-earth/thickest-layer-earth-mantle/
https://www.sciencedirect.com/science/article/abs/pii/0012821X9390219Y
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An age map from newest (red) to oldest (violet) overlaid over tectonic plates. The youngest areas of seafloor
spread. Image via Wiki Commons.
Then, on the other side, we have plate collision: we see this brilliantly in the case of the Himalayas. The Himalayan
mountain range, the tallest on Earth, formed as the Indian plate smashed into Asia. Imagine pushing two pieces of
paper toward each other: they crumple and push upwards. That’s what’s happening in the Himalayas… except far
more complex.
Plate tectonics wasn’t accepted initially. But after several seminal papers, the position of most geologists started to
change. Nowadays, plate tectonics is almost universally accepted.
Types of tectonic plates
Tectonic plates are the massive pieces of the Earth’s lithosphere that move, interact, and change over time. They’re
kind of like cracked shell pieces moving around on a viscous surface (the mantle).
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Depiction of oceanic and continental crust, overlaid on the mantle.
There are two primary types of tectonic plates: oceanic plates and continental plates.
1. Oceanic Plates: These are tectonic plates located under the ocean. They are primarily composed of basalt, a
dense rock formed from solidified lava. Examples of oceanic plates include the Pacific Plate and the Nazca
Plate.
2. Continental Plates: These are tectonic plates that form the continents. They are primarily composed of
granite, a less dense rock than basalt. Examples of continental plates include the North American Plate and the
Eurasian Plate.
As the name implies, oceanic plates consist of oceanic crust — while continental plates consist of continental crust.
Continental crust is thicker but lighter than the oceanic crust. This is because the rocks in the oceanic plates (basalts)
are denser.
This also helps to explain what happens when tectonic plates collide. When an oceanic plate collides with a
continental plate, the denser oceanic plate tends to slide under and is recycled in the mantle. This process is called
subduction (we’ll get to it in more detail in a moment).
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But when two continental plates collide, they have similar densities, so it’s not easy for one to slide beneath the other.
So what basically happens is that they crumple up. This process is what lead to the formation of some of the tallest
mountain ranges on Earth, like the Himalayas.
Of course, these processes are not simple. In fact, geologists today are still actively researching all these tectonic
processes, trying to figure out exactly what happens. It’s not easy, but we’re getting more and more information, and
our understanding of plate tectonics, while still incomplete, is improving every year.
“Most present-day motions of the earth’s plates are well understood. We have known since the 1960s
that plate motion is very concentrated in the oceans, but more diffuse [elsewhere], especially in Asia. We
still don’t understand that diffuse motion very well. When in the earth’s history plate tectonics started is
still widely debated,” says Lynn Sykes, one of the pioneering seismologists who worked on plate
tectonics.
Tectonic plate map
Among the vast array of geological maps researchers use, the tectonic map is one of the most important.
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There are seven major tectonic plates on Earth:
1. Pacific Plate: The largest tectonic plate, the Pacific Plate, is mostly an oceanic plate covering the Pacific
Ocean. This plate extends from the east coast of Japan to the western coast of North America.
2. North American Plate: This plate includes not only North America but also part of the Atlantic Ocean and the
western part of the Arctic Ocean. It extends eastward to the Mid-Atlantic Ridge and westward to a complex
boundary with the Pacific Plate.
3. Eurasian Plate: Covering most of Europe and Asia, the Eurasian Plate extends from the Mid-Atlantic Ridge in
the west to the Indian Ocean in the east.
4. African Plate: This plate includes the entire continent of Africa as well as the surrounding oceanic crust of the
Atlantic and Indian Oceans.
5. Antarctic Plate: As the name suggests, this plate covers the continent of Antarctica and extends into the
surrounding Southern Ocean.
6. Indo-Australian Plate: This plate is often considered as two separate plates – the Indian Plate and the
Australian Plate – due to the different movement rates. It covers the Indian Ocean, Australia, and part of the
Pacific Ocean.
7. South American Plate: This plate includes the continent of South America and a portion of the Atlantic Ocean
extending to the Mid-Atlantic Ridge.
Thesemajor tectonic plates interact with each other at their boundaries, leading to various geological phenomena
and shaping the Earth’s landscape.
You could say that these plates correspond to the continents on Earth, but that’s only approximately true, and there
are still some that don’t correspond to any continent. But perhaps a better way to put it is that our current,
geographical continents don’t correspond to the real geological continents. When researchers say they’ve found a
new continent, for instance, they’re referring to a new piece of plate tectonics.
In addition to these, there are also several minor tectonic plates and microplates.
Plate boundaries
Just like how plate tectonics are categorized, so too are their boundaries.
Divergent boundaries
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Diagram of a divergent tectonic boundary.
Divergent boundaries, also known as constructive boundaries, are areas where tectonic plates move apart from each
other. This movement is driven by the upwelling of magma from the Earth’s mantle, which creates new crust as it
cools and solidifies. This is where the “constructive” part comes from.
1. Formation and Characteristics: Divergent boundaries are characterized by a process known as seafloor
spreading, where new oceanic crust is formed through volcanic activity and then gradually moves away from
the ridge. This process often results in the formation of mid-ocean ridges, which are underwater mountain
ranges formed by plate divergence. The Mid-Atlantic Ridge is a prime example of this.
2. Geological Features: Divergent boundaries can lead to the formation of various geological features.
Underwater, they create mid-ocean ridges and can lead to the formation of new islands through volcanic
activity. On land, they can create rift valleys, such as the East African Rift, where the continental crust is being
pulled apart.
3. Volcanic and Seismic Activity: Divergent boundaries are typically associated with significant volcanic and
seismic activity. As the plates move apart, magma rises to fill the gap, often leading to volcanic eruptions.
Earthquakes can also occur as the crust fractures and moves.
4. Role in Plate Tectonics: Divergent boundaries play a crucial role in plate tectonics as they facilitate the
creation of new crust. This process contributes to the continuous cycle of crust formation and destruction that
drives the movement of tectonic plates.
5. Examples: Some notable examples of divergent boundaries include the Mid-Atlantic Ridge, the East Pacific
Rise, and the East African Rift. These locations provide valuable opportunities for scientists to study the
processes occurring at divergent boundaries.
Convergent boundaries
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Image of a convergent tectonic boundary (with subduction).
Convergent boundaries, also known as destructive boundaries, are regions where tectonic plates move towards each
other. This movement can lead to various geological phenomena, including the formation of mountain ranges, deep
sea trenches, and volcanic activity. Here are some key details about convergent boundaries:
1. Formation and Characteristics: Convergent boundaries form when two tectonic plates collide. This collision
can involve two oceanic plates, an oceanic and a continental plate, or two continental plates. The nature of the
plates involved determines the specific geological phenomena that occur.
2. Subduction Zones: When an oceanic plate collides with another oceanic plate or a continental plate, the
denser oceanic plate is usually forced under the other in a process known as subduction. This leads to the
formation of a deep sea trench and can cause intense volcanic activity.
3. Mountain Formation: When two continental plates collide, neither plate is dense enough to subduct under the
other. Instead, the crust is pushed upwards, leading to the formation of mountain ranges. The Himalayas, for
example, were formed by the collision of the Indo-Australian and Eurasian plates.
4. Volcanic and Seismic Activity: Convergent boundaries are associated with significant volcanic and seismic
activity. The subduction of one plate under another can lead to the formation of volcanic arcs, while the intense
pressure and friction at these boundaries can trigger powerful earthquakes.
5. Examples: Notable examples of convergent boundaries include the collision between the Eurasian and Indian
plates (forming the Himalayas), the subduction of the Nazca Plate beneath the South American Plate (forming
the Andes), and the subduction of the Pacific Plate beneath the Mariana Plate (forming the Mariana Trench).
Transform boundaries
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Image of a transform boundary.
Transform boundaries, also known as conservative boundaries, are regions where two tectonic plates slide past each
other horizontally. These boundaries are unique in the sense that they neither create nor destroy the lithosphere.
Here are some key details about transform boundaries:
1. Formation and Characteristics: Transform boundaries form when two tectonic plates slide past each other
horizontally. This lateral movement is due to the differential rates of seafloor spreading at divergent boundaries.
The edges of the plates at these boundaries are often jagged, leading to the plates becoming locked together,
causing a build-up of stress.
2. Faults and Earthquakes: The primary geological feature associated with transform boundaries is faults,
specifically strike-slip faults. These faults occur when the movement along the fault line is horizontal. The stress
build-up from the locked plates can eventually be released in the form of an earthquake. Therefore, transform
boundaries are often associated with seismic activity.
3. Notable Examples: The most famous example of a transform boundary is the San Andreas Fault in California,
where the Pacific Plate and the North American Plate slide past each other. Other examples include the North
Anatolian Fault in Turkey and the Dead Sea Transform fault in the Middle East.
4. Role in Plate Tectonics: Transform boundaries play a crucial role in plate tectonics as they accommodate the
movement between other types of boundaries. They often connect segments of diverging or converging
boundaries, forming a complex network of geological activity.
5. Impact on Landscape: Unlike convergent and divergent boundaries, transform boundaries do not result in
significant changes to the Earth’s topography. However, the intense seismic activity can lead to noticeable
surface shifts and damage in populated areas.
Beyond plate tectonics
It hasn’t been long since plate tectonics was accepted as the major unifying geological theory. It’s striking to think that
we developed nukes before we figured out how earthquakes happen — and it’s also pretty humbling. We don’t know
everything about plate tectonics, and we may never understand truly everything, but with each study, we’re getting
one more puzzle piece.
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We know the forces that drive plate motion — or we think we do — but we don’t know many of the details.
Furthermore, no mechanism can be truly tested to explain everything about plate tectonics. But perhaps the biggest
unknown regarding plate tectonics is that no known mechanism can explain all the facets of plate movement. The
currents inside the mantle, the ones that drive all this, are still pretty mysterious.
Could there be yet another, even better theory that comes up eventually? It’s definitely possible. It’s also possible that
our plate tectonics knowledge is still rough and needs finessing.
The fact that tectonic plates exist, that they’ve been moving in the past, and are continuing to move now is
undeniable. The fact that this shapes our planet is also well understood. But the details of why and how they move is
still an area of active research. To make matters even more complex, there could be plate tectonics on other celestial
bodies, which we currently know very little about. No doubt, there’s still plenty of work to do when it comes to these
tectonic plates.
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