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  • Once upon a time,

  • South America lived harmoniously alongside Africa

  • until a crack in the Earth

  • drove the two continents apart.

  • This breakup began about 200 million years ago

  • during the separation of the supercontinent

  • known as Pangaea.

  • Their proximity back then

  • explains why the same plant fossils and reptile fossils,

  • like the Mesosaurus,

  • can be found on the South American east coast

  • and African west coast.

  • However, this evidence does not account forhow the continents moved apart.

  • For that, we'll need to take a close look

  • at the earth below our feet.

  • Though you may not realize it,

  • the ground below you is traveling across the Earth

  • at a rate of about 10 cm/year,

  • or the speed at which your fingernails grow.

  • This is due to plate tectonics,

  • or the large-scale movement of Earth's continents.

  • The motion occurs within the top two layers of the Earth's mantle,

  • the lithosphere and asthenosphere.

  • The lithosphere, which includes the crust and uppermost mantle,

  • comprises the land around you.

  • Beneath the lithosphere

  • is the asthenosphere

  • the highly viscous but solid rock portion of the upper mantle.

  • It's between 80 and 200 km below the Earth's surface.

  • While the asthenosphere wraps around the Earth's core as one connected region,

  • the lithosphere is separated on top into tectonic plates.

  • There are seven primary tectonic plates

  • that compose the shape of the planet we know today.

  • Like the other smaller tectonic plates,

  • the primary plates are about 100 km thick

  • and are composed of one or two layers:

  • continental crust and oceanic crust.

  • Continental crust forms the continents

  • and areas of shallow water close to their shores,

  • whereas oceanic crust forms the ocean basins.

  • The transition from the granitic continental crust

  • to the basaltic oceanic crust

  • occurs beyond the continental shelf,

  • in which the shore suddenly slopes down

  • towards the ocean floor.

  • The South American Plate is an example

  • of a tectonic plate made of two crusts:

  • the continent we know from today's map

  • and a large region of the Atlantic Ocean around it.

  • Collectively comprising the lithosphere,

  • these plates are brittler and stiffer

  • than the heated, malleable layer of the asthenosphere below.

  • Because of this,

  • the tectonic plates float on top of this layer,

  • independently of one another.

  • The speed and direction in which these tectonic plates move

  • depends on the temperature and pressure

  • of the asthenosphere below.

  • Scientists are still trying to nail downthe driving forces behind this movement,

  • with some theories pointing towards mantle convection,

  • while others are examining

  • the influence of the Earth's rotation

  • and gravitational pull.

  • Though the mechanics have not been sorted out,

  • the scientific community agrees

  • that our tectonic plates are moving and have been for billions of years.

  • Because these plates move independently,

  • a fair amount of pushing and pulling

  • between the plates occurs.

  • The first type of interaction

  • is a divergent boundary,

  • in which two plates move away from one another.

  • We see this in the Mid-Atlantic Ridge

  • between South America and Africa.

  • The next interaction is when two plates collide,

  • known as a convergent boundary.

  • In this instance, the land is pushed upward

  • to form large mountain ranges,

  • like the Himalayas.

  • In fact, the Indian Plate is still colliding

  • with the Eurasian Plate,

  • which is why Mount Everest

  • grows one cm/year.

  • Finally, there's the transform boundaries,

  • where two plates scrape past one another.

  • The grinding of the transform boundary

  • leads to many earthquakes,

  • which is what happens

  • in the 810 mile-long San Andreas Fault.

  • The moving Earth is unstoppable,

  • and, while a shift of 10 cm/year may not seem like a lot,

  • over millions of years our planet will continue

  • to dramatically change.

  • Mountains will rise,

  • shorelines will recede,

  • islands will pop up.

  • In fact, one projected map shows

  • the cities of Los Angeles and San Francisco

  • on top of each other.

  • Maybe South America and Africa

  • will come together again, too.

  • Only time will tell.

Once upon a time,

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B2 H-INT US TED-Ed tectonic crust earth mantle continental

【TED-Ed】The Pangaea Pop-up - Michael Molina

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    Kevin Tan posted on 2014/08/14
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