Pratique du Shadowing: The Graveyard at the Center of the Earth - Apprendre l'anglais à l'oral avec YouTube
C2
Without plate tectonics, the Earth would look very different than it does today.
219 phrases
Si les phrases sont trop courtes ou trop longues, cliquez sur Edit pour les ajuster.
1
Without plate tectonics, the Earth would look very different than it does today.
2
Our mountain ranges, oceans, volcanoes,
3
and even entire continents all get their recognizable features from the shifting rock plates on the Earth's mantle.
4
And those features are pretty good evidence that plate tectonics works.
5
But knowing if something works doesn't always mean we know why or how it works.
6
And when it comes to plate tectonics,
7
continents move in complicated ways.
8
Scientists have been trying to solve the mystery of why plate tectonics works the way it does for over a hundred years,
9
and they might have just uncovered a key to cracking it.
10
The answer may be buried in a bizarre mirror world deep inside the Earth,
11
where movement beneath the surface looks a lot like it involves the remains of former crustal rocks.
12
Places of crusts we thought disappeared hundreds of millions of years ago,
13
but now live inside the planet,
14
like a graveyard of ancient plates.
15
When scientists first embraced plate tectonics around the 1960s,
16
the theory explained many observations about the planet.
17
The idea
18
that Earth's surface is made of rocky plates moving over a
19
molten mantle explains why large mountain ranges form in the middle of oceans, for example.
20
as Earth's mantle is creating new plates.
21
And why deep trenches form at the edges of the oceans,
22
where one plate is diving beneath another.
23
Tying together these observations, geologists realize that tectonics works as a system.
24
Plates are created at mid-ocean ridges,
25
then move away from them and finally disappear back into the Earth at subduction zones,
26
creating most volcanoes and many large earthquakes in the process.
27
But even though the theory that recognized the constant cycle by which landforms are created was a breakthrough,
28
it didn't exactly explain how this happens.
29
What force could move massive plates,
30
which can weigh a made-up sounding 5 quintillion tons around like driftwood?
31
Early in the days of plate tectonic theory,
32
geologists and geophysicists assumed plates move because of mantle convection.
33
Currents of hot, molten material rising inside the Earth push the plates,
34
dragging them along the surface the way rising bubbles move foam in a pot of boiling water.
35
Logically, that idea makes sense.
36
But scientists quickly realized that the physics of mantle convection don't totally add up.
37
Now, the mantle definitely does have currents.
38
Since 1971, scientists have known that rising plumes of magma travel from deep inside the Earth to the surface,
39
creating islands like Hawaii and Iceland.
40
But around the same time,
41
researchers also realized something about the mantle's makeup that complicates the effect those currents could possibly have.
42
See, they were looking at how continents move during ice ages,
43
when the weight of massive ice sheets pushed them down into the mantle.
44
And how, when the ice later melted,
45
the same continents began popping back up.
46
So they used data from a satellite to measure the gradual upward movement of the continent relative to the ocean's surface,
47
to see just how fast the now deglaciated continents were popping back up.
48
And even though they couldn't see the mantle below the continents,
49
knowing the rate at which the mantle pushed continents up let scientists calculate its viscosity,
50
that is, how runny it is.
51
They found that the Earth's mantle is much runnier than expected.
52
Later researchers estimated that the mantle is about a billion times runnier than the lithosphere,
53
or crust, that sits on top of it.
54
So those mantle currents simply couldn't be enough to move the plates the way we know they move.
55
There must have been another force helping propel this movement.
56
Even more mysteriously, geophysicists modeling Earth's mantle and continents found the Earth should have what's called a stagnant lid,
57
where the lithosphere sits in place on the surface as mantle currents move underneath.
58
In fact, Earth is the only place we know,
59
for sure, where continents move,
60
crash into each other, rise, and fall.
61
So why does Earth have such unique tectonics?
62
It all comes back to the mantle,
63
which, as scientists noted back in the 1960s,
64
shapes an important feature of tectonic subduction.
65
That's the process where plates slip underneath another,
66
driving back towards the center of the planet.
67
And while it's another process that we can't directly see,
68
it's one scientists inferred must be taking place once they noted some odd features of earthquakes.
69
With the installation of big seismograph networks,
70
geophysicists could suddenly tell exactly where and how deep earthquakes happened.
71
And when they looked at big tremors in places like Alaska,
72
they saw earthquake epicenters were far below the crust.
73
In fact, some earthquakes were happening hundreds of kilometers down inside the mantle.
74
That suggests that the stress of the plate bending deep down is triggering these earthquakes.
75
Researchers realized that these quakes were like a sonar scan,
76
revealing locations of where plates were driving down into the mantle.
77
They were seeing the edge of the subducting plate that had disappeared under another plate long ago.
78
Earth is also the only planet we know where subduction connects the surface to the interior in a major way.
79
And scientists soon figured out that subduction helps explain why tectonics works the way it does.
80
Because as geologists reasoned, if plate edges sank into the mantle,
81
they'd likely pull on the rest of the plate, dragging it along.
82
Initially, this was purely logical speculation.
83
Again, we can't see any of this.
84
But when scientists plugged this new force,
85
called slab-pull, into models, the calculations worked better than mantle convection alone.
86
But even with extra force from slab-pull added into the equation,
87
the models still didn't quite fit Earth's tectonics.
88
Plates still moved faster than the models predicted.
89
There must be other forces helping move the continents.
90
So scientists kept digging.
91
In the mid-1970s, they noted that mid-ocean ridges are usually topographic highs.
92
So as new plate material moves away from the ridges,
93
it travels downward, as if descending from a mountain.
94
This is due to gravity pulling down,
95
adding a little force in the process scientists call ridge push.
96
And scientists found this does help move us closer than the two forces of convection and slab pull alone.
97
But according to the models,
98
the addition of ridge push still wasn't enough to explain how fast our continents move either.
99
There had to be something else,
100
at least one more factor.
101
Scientists then turned to another possible force acting on continents in the 1980s,
102
something they called slab suction.
103
Slab suction happens when the mantle flows around a sinking plate edge,
104
pulling it downward more than just gravity alone.
105
Like in movies, where people swimming away from a sinking ship get sucked underwater as the boat disappears below the surface.
106
So in the early 2000s,
107
scientists added slab suction to their models,
108
and found this matched observed plate movements a lot more than before.
109
So now we have four forces helping move continents.
110
Mantle convection, ridge push, slab pull from the weight of the plate sinking into the Earth,
111
and slab suction pulling even harder as those plates get sucked into the lower mantle.
112
Adding together all these forces,
113
we get a better idea of why Earth's tectonics works.
114
Plates are created at mid-ocean ridges,
115
and get pushed away from those ridges by gravity and mantle currents.
116
Eventually, plates dive back into the mantle,
117
pulling the plates along, with suction then dragging them down even harder.
118
But what makes those pieces subduct and sink back into the mantle?
119
This isn't something we see happening on any other planets in our solar system.
120
This is where the bizarre mirror world comes in.
121
See, seismic studies done in the mid-2010s show two huge zones of something unusual at the base of the mantle,
122
one below the Pacific Ocean and another underneath Africa.
123
When seismic waves hit these zones,
124
they slow down, unlike how they move through the rest of the mantle.
125
Geophysicists call these massive 15,000-kilometer-wide features large, low-velocity provinces, or LLVPs.
126
They can tell from the way LLVPs react seismically that they're probably denser than the surrounding mantle,
127
and possibly made of different material.
128
And the strangest thing is,
129
these LLVPs seem to move around much the same way continents do on the Earth's surface.
130
They collide, assemble, and possibly even break apart, just like continents.
131
In fact, scientists recently uncovered evidence
132
that some of them might actually contain the remains of continents that used to be on the Earth's surface.
133
Continents we thought disappeared hundreds of millions of years ago.
134
The geophysicists running the models to figure out what LLVPs might be made of found
135
that they could be the remains of old surface plates that sunk towards the core of the Earth in a giant pile,
136
like a graveyard.
137
The idea of this slab graveyard could explain a few things we see at the surface.
138
Like how erupting lavas in places like Hawaii are oddly enriched in the isotope helium-3.
139
Or how volcanoes in both the South Pacific and off the West African coast erupt unusually high amounts of uranium.
140
Those are both elements we'd expect to see on Earth's surface,
141
rather than in plumes from the mantle.
142
But helium and uranium makes more sense if remnants of Earth's surface,
143
sunk deep into the mantle, are feeding plume eruptions.
144
So those mirror slabs inside the lower mantle are probably,
145
at least partly, the remains of old plates that got subducted and then sank.
146
And there, invisible to us at the surface,
147
it seems they continue to play a role in plate tectonics.
148
Like, they probably determine mantle currents.
149
When plotting major mantle plumes that have erupted onto Earth's surface,
150
geologists notice that they all seem to burst forth from LLVP zones.
151
And these could also be the reason we have subduction.
152
Although most subduction zones lie well away from these deep earth structures,
153
it might be the case that mantle currents rise above LLVPs,
154
pushing plates off to the sides.
155
Then once the plates are pushed away from the upwelling plumes above LLVPs,
156
they start to sink, subducting.
157
When researchers plug in all the data we have on the mantle and the movements of continents,
158
that scenario is exactly what they see.
159
And it all comes full circle when the sinking plates absorb back into the LLVP graveyard,
160
deep in the mantle, and the cycle continues.
161
Now, not all scientists agree with this theory.
162
For example, there's debate about whether mantle plumes rise from the center of LLVPs or from their edges.
163
Scientists also argue about whether LLVPs stay in one place or migrate around the mantle.
164
Another hypothesis argues that LLVPs are actually the remnants of an ancient planet that crashed into early Earth,
165
which we talk about in our episode When Earth Ate a Planet.
166
Overall, LLVPs are pretty mysterious.
167
Even after decades of research into plate tectonics,
168
and a solid understanding of how it works,
169
the question of why it works has been harder to pin down.
170
But it appears that from deep in the Earth,
171
this ancient mirror world has something to do with driving tectonics,
172
the thing that makes our planet unique,
173
as far as we know.
174
And given that the mirror plates seem as active as the surface continents,
175
the future of tectonics could be as surprising as this bizarre discovery itself.
176
Eons is possible thanks to rad viewers like you,
177
who back us on Patreon.
178
Your support of our videos through Patreon is vital in keeping our educational mission going.
179
Whether it's the research and production of our videos,
180
commissioning accurate paleoart, and of course,
181
paying our wonderful hosts, this all happens thanks to your support.
182
Patrons get access to special videos from our hosts,
183
digital puzzles with our paleoart,
184
and at the Eontologist level, shoutouts in our episodes.
185
To show our thanks, we're declaring Patron Appreciation Month.
186
Become a patron at the Paleozoic level by March 31st,
187
and you will get the very first Eons Trading Card,
188
created by our team of paleo artists and writers.
189
This art is also featured on our new Permian t-shirt, which absolutely rules!
190
Many Eons viewers remember that for a good long time,
191
our videos used to end with a shout out to one of our patrons, Steve.
192
Now you can be Steve,
193
a super terrific, extremely vital Eontologist.
194
Where every month we have 50 members in this new Patreon tier,
195
we'll shout out Steve in our videos.
196
And to celebrate with the entire Eons community this Patron Appreciation Month,
197
there will be a livestream on March 27th, 2025.
198
Thank you for all your support.
199
So we're still figuring out the details of plate tectonics,
200
but we can clearly see the effects on our modern world,
201
if you know where to look.
202
Join Michelle Barbosa-Ramirez and Blake DePastino on a field trip to explore the epic natural history saga of LA in our episode,
203
How Plate Tectonics Transformed Los Angeles.
204
We gotta thank this month's Tectonic Eontologists.
205
Addie, Annie and Eric Higgins,
206
Carl Wolfel, Jackie Scott Ralston,
207
Jake Hart, John Davidson Ng,
208
Juan M, Melanie Lam Carnivale,
209
Nico Robin, and Raphael Hassa.
210
Become an Eonite at patreon.com slash eons and you can get fun perks like access to a monthly digital paleo art puzzle.
211
And as always, thank you for joining me in the Ken Barnes studio.
212
Subscribe at youtube.com slash eons for more adventures and deep time.
213
Continental Drift came out in 1912 and everybody was like,
214
y'all crazy, y'all crazy.
215
And then around the 1960s they were like,
216
eh, maybe you're not as crazy as we thought you were.
217
So it took like 50 years for scientists to be like,
218
nah, this is real.
219
This is, this is it.
Télécharger l'application
Notation IA pour chaque phrase que vous prononcez
TRENDING
Populaires
Context & Background
The video "The Graveyard at the Center of the Earth" delves into the fascinating subject of plate tectonics—how the Earth's structure is shaped by shifting rock plates in its mantle. The speaker discusses how these movements create our mountains, oceans, and geological events like earthquakes and volcanoes. However, the complexity of these tectonic movements has puzzled scientists for over a century, leading them to explore new theories about the forces behind this dynamic system. Understanding these concepts can significantly enhance your vocabulary and comprehension, especially in academic contexts, making it beneficial for learners of English who wish to engage in scientific discussions.
Top 5 Phrases for Daily Communication
- Plate tectonics - A key concept in geology referring to the movement of the Earth's plates.
- Mantle convection - The process by which heat from the Earth's interior causes molten material to rise and fall, influencing plate movement.
- Subduction zone - An area where one plate sinks beneath another, shaping both the ocean's trenches and volcanic activity.
- Crustal rocks - The outermost layer of the Earth that is involved in tectonic movements.
- Viscosity - A measure of a fluid's resistance to flow; understanding this term can help in comprehending geological processes.
Step-by-step Shadowing Guide
To effectively improve your English pronunciation while watching this video, follow this step-by-step shadowing guide:
- Watch Actively: Begin by watching the video without any distractions. Pay close attention to the terminology used and how the speaker articulates their thoughts.
- Segment the Transcript: Divide the transcript into smaller sections. This will make it easier to focus on specific phrases and pronunciations, particularly complex scientific terms.
- Repeat the Phrases: As you listen, pause after each sentence or key phrase to repeat what you hear. This practice of shadowspeak helps to improve English pronunciation by mimicking the rhythm and intonation of the speaker.
- Record Yourself: After practicing, record your voice as you repeat the phrases. Compare your pronunciation with the original speaker to identify areas for improvement.
- Use Context: Try to use the phrases you’ve practiced in your conversations. Whether discussing scientific topics or everyday events, integrating these new terms into your vocabulary will aid retention.
Utilizing a shadowspeak approach while learning with the help of resources like YouTube can dramatically enhance your speaking skills and confidence. Remember to regularly revisit these phrases and concepts to reinforce your learning.
Qu'est-ce que la technique du Shadowing ?
Le Shadowing est une technique d'apprentissage des langues fondée sur la science, développée à l'origine pour la formation des interprètes professionnels. Le principe est simple mais puissant : vous écoutez de l'anglais natif et le répétez immédiatement à voix haute — comme une ombre suivant le locuteur avec un décalage de 1 à 2 secondes. Les recherches montrent une amélioration significative de la précision de la prononciation, de l'intonation, du rythme, des liaisons, de la compréhension orale et de la fluidité.
☕ Offrez-nous un café
ShadowingEnglish reste 100% gratuit grâce à votre soutien. Les coûts des serveurs et de l'IA sont élevés — votre café nous aide à continuer ! 🙏