C'est incroyable d'y penser, mais les continents n'ont pas sombré dans la lave grâce au fonctionnement de la croûte terrestre. La croûte, qui inclut les continents, est comme un gigantesque puzzle de plaques solides flottant sur une couche pâteuse appelée le manteau. Même si le manteau est chaud et partiellement en fusion, il est suffisamment dense pour maintenir la croûte en flottation au lieu de la laisser sombrer. De plus, les continents sont composés de roches plus légères et moins denses comparé aux fonds océaniques plus lourds, donc ils restent naturellement à la surface. Les plaques tectoniques de la Terre peuvent se déplacer et entrer en collision, mais elles sont étonnamment résistantes sur des millions d'années. Ainsi, bien qu'il y ait beaucoup de roches en fusion sous nos pieds, les continents ne risquent pas de sombrer de si tôt ! Animation créée par Sympa.
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FunTranscript
00:00At first glance, it seems that we live on a giant raft called continent,
00:06which floats on lava in fusion, waiting to hit another continent.
00:11But let's stop for a moment in a high school science class.
00:16Our planet looks like a cake,
00:18with different layers of ingredients stacked on top of each other,
00:22the core, the mantle and the crust of the earth.
00:25Where is the icing?
00:27The cake dough on top represents the crust of the earth,
00:31composed of three types of tasty rocks,
00:33igneous, sedimentary and, say it with me, metamorphic.
00:39These rocks are formed in different ways,
00:42for example from solidified lava or deposits of particles and minerals.
00:47The crust is what we rely on,
00:49it shelters our continents, our oceans and everything we see around us.
00:54Then comes the mantle,
00:56i.e. the layer just below the crust.
00:59Many people think that the mantle is nothing but lava,
01:02but this is not entirely true.
01:04Just as you mix different ingredients in your cake dough,
01:08the mantle is made up of different types of moving rocks
01:11and moves all the time.
01:14Finally, we come to the sweetest part,
01:16the center or, in the case of the earth, the core.
01:20It is made up of two parts,
01:22the external core and the internal core.
01:24The external core is made up of rocks and melting metals
01:28that are incredibly hot,
01:30even hotter than the surface of the sun.
01:33The internal core is solid,
01:35even if the temperatures there are crazy,
01:37it does not become liquid because the pressure there is incredibly strong.
01:41Seeing all this,
01:43we can easily imagine that there are under our feet
01:45kilometers of lava and burning rocks.
01:49So, how do tectonic plates move?
01:53The continents do not float on a sea of melted rocks.
01:56Oceanic and continental crusts actually rest on a mantle.
02:00Certainly, there is a liquid layer of rocks in our planet.
02:04The external core, located about 2,900 km below the surface,
02:09but we are separated by the mantle, which is thick and solid.
02:13The tectonic plates of the earth move
02:16because they rest on a thick layer of solid rocks, the upper mantle.
02:21In fact, this rock is subjected to pressure and incredible heat,
02:26which makes it flow slowly.
02:29It is a bit like the honey or syrup
02:31that you pour on the layers of your cake.
02:33When you move the mold,
02:35the honey or syrup moves and flows.
02:38Similarly, the upper mantle can flow
02:40and drag the parts that are above it,
02:43but much slower than honey.
02:45The rock is both brittle and flexible.
02:48It can crack and break like a biscuit.
02:50I'm starting to get hungry, me.
02:52But it can also stretch and bend like a piece of caramel.
02:56When the plates cling to each other,
02:59they can no longer move,
03:00but when they free themselves,
03:02they begin to drift again,
03:04like puzzle pieces that move
03:06until they encounter a new obstacle.
03:08These are temperatures and extremely high pressure
03:11that are at the origin of this flow.
03:13It's like a big marmite of soup on fire.
03:16When the soup heats up,
03:17it starts to move,
03:19carrying the heat from one place to another.
03:21It's lunchtime.
03:23Speaking of lunch, I mean lava.
03:25It's not just the melting rocks
03:27that rise from the outer core to the volcano.
03:29When the tectonic plates come in contact
03:31and slide from one to the other,
03:33their friction creates a lot of heat and pressure.
03:36It's like when you rub your hands in the cold,
03:39they end up warming up.
03:41Or when you light a fire with stones,
03:43and when the molten rock, or magma,
03:45rises to the surface,
03:47it gives us volcanoes.
03:49A long time ago,
03:50the Earth was not divided into continents
03:52as it is today.
03:54Instead,
03:55there was a giant terrestrial mass
03:57known as Pangea,
03:59which means the whole Earth in Greek.
04:01Imagine that you are stuck
04:03in the middle of a gigantic ocean.
04:06Over time,
04:07this supercontinent slowly disintegrated.
04:09These parts moved away from each other
04:11and formed the separate lands
04:13that we call continents.
04:14This idea appeared for the first time
04:16in the 16th century,
04:17when a cartographer realized
04:19that the coasts of Africa,
04:20America and Europe
04:21seemed to fit together like puzzle pieces.
04:24Later,
04:25researchers realized
04:26that the rocky composition of these coasts
04:28was similar,
04:29which means that they used to be part
04:31of a giant mass,
04:32and they called it
04:33the theory of the drift of continents.
04:35At first,
04:36people were rather skeptical
04:38because they wondered
04:39how such massive lands
04:41could move.
04:42Today,
04:43we would all be able to explain it,
04:45wouldn't we?
04:47The Earth's crust is therefore
04:49divided into some very large plates
04:51and into many other smaller ones.
04:54They are all moving,
04:56even if it is slowed down.
04:58We cannot feel it
05:00and we will not see any particular change
05:02during our life.
05:04It is a process
05:05that lasts hundreds of millions of years.
05:08When the plates move,
05:10they interact with each other
05:12in a fascinating way.
05:14For example,
05:15when two plates collide,
05:17one can be pushed under the other,
05:19which contributes to creating
05:20a subduction zone.
05:22Over time,
05:23this is how we get
05:24interesting things
05:25like volcanic islands,
05:27pits
05:28and even mountain ranges.
05:32The plates apparently
05:33began to move
05:34about 3 to 5 billion years ago.
05:37It took them some time
05:39to regroup
05:40and form the first supercontinent
05:42we know of,
05:43called Ur.
05:46Today,
05:47these remains
05:48are parts of Madagascar,
05:49India
05:50and Australia.
05:52The Pangea was born
05:54335 million years ago,
05:57but it will probably not be
05:58the last supercontinent to form.
06:02Thus,
06:03in the distant future,
06:04new generations
06:05will be able to live
06:06on what is called
06:07the next Pangea.
06:11When the oceanic crust
06:12of the Atlantic
06:13will slowly take its place
06:14under the continental crust,
06:17the oceanic basin
06:18of the Atlantic will close,
06:19which explains
06:20that the continents
06:21will end up getting closer.
06:24This means
06:25that the Americas
06:26will meet Africa
06:27and that Eurasia
06:28will be overturned on the side.
06:30Men will therefore be able
06:31to live on a giant
06:32continental mass
06:33in the shape of a ring,
06:34grouped around
06:35the interior sea
06:36or at least
06:37what is left of it.
06:39Or the continents
06:40will take another direction
06:41and form another puzzle
06:43called the Massif.
06:46In this scenario,
06:47the Americas will drift
06:48to the West,
06:49merge with Australia
06:50and pivot to Siberia.
06:53And that's not all.
06:55The new Pangea
06:56is the scenario
06:57in which the Americas
06:58will meet
06:59to embrace
07:00Antarctica and Australia.
07:01While Africa
07:02moves away
07:03to the Northwest.
07:04In fact,
07:05all the continents
07:06will meet
07:07to form a giant
07:08continental mass
07:09that extends
07:10from one pole to the other.
07:12Do you want more?
07:14Let's go.
07:16There is also
07:17the Orica hypothesis,
07:18which is similar
07:19to the new Pangea.
07:20Only here,
07:21all the continents
07:22will come together
07:23to form a gigantic land
07:24that concentrates
07:25around the equator.
07:27Hmm,
07:28a nice place to live,
07:29with a permanent sun
07:30and endless days
07:31at the beach.
07:34And who knows
07:35what kind of ditches,
07:36mountains,
07:37islands
07:38and other
07:39magnificent geological
07:40beauties we would get
07:41with this super giant
07:42continent.
07:44The Pangea
07:45dislocated about
07:46175 million years ago.
07:48When the Atlantic
07:49and Indian Oceans
07:50began to expand
07:51to the East,
07:52the belt of fire
07:53formed.
07:55It is a tract
07:56that stretches
07:57the Pacific Ocean,
07:58where earthquakes
07:59are frequent
08:00and active volcanoes.
08:02The Pangea
08:03could not cross
08:04this border
08:05and continue
08:06to move to the West.
08:07Now,
08:08the Pangea
08:09can move laterally
08:10along the belt of fire.
08:12The subduction areas
08:13act in some way
08:14like a barrier
08:15that forces
08:16the tectonic plates
08:17to progress
08:18in different directions.
08:19Thus,
08:20the Pangea
08:21could possibly
08:22collide with the Americas
08:23and form something
08:24similar to the Pangea.
08:26As I would like
08:27to sit comfortably
08:28with popcorn
08:29to witness
08:30this magnificent spectacle,
08:31but this will not happen
08:32before at least
08:3350 million years.
08:35I feel that
08:36I will no longer be there
08:37at this moment.
08:39Different theories
08:40evoke different possibilities
08:41for the next
08:42supercontinent.
08:44But it seems
08:45that it will probably
08:46be somewhere
08:47in the polar zone,
08:48around what we
08:49call today
08:50the Arctic Ocean.
08:52Bear,
08:53this is not my cup of tea,
08:54bring me the sun.
08:56No,
08:57it's more important
08:58that you don't.
08:59I like,
09:00by human means,
09:01your idea.
09:02Tentatively.