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Course: Middle school Earth and space science > Unit 4
Lesson 3: Plate tectonicsPlate tectonics and the ocean floor
In the ocean, tectonic processes continuously create and destroy oceanic crust. When tectonic plates collide, denser plates dive under less dense ones, creating trenches and mountains. New sea floor is constantly created as plates move apart, keeping Earth from shrinking. Created by Khan Academy.
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- if there was a super continent then couldn't there be another someday(11 votes)
- Yes, scientists predict in the future that the continents will someday come back together but in a different form.(5 votes)
- When plates smash into each other at higher speeds, more of the crust at the collision sites becomes brittle, and that makes the region more prone to large quakes.(6 votes)
- Why would anyone want to go explore the ocean floor? That sounds scary. I hope I never go down there, water or no water. I don't like seeing angler fish or goblin sharks, although I've never seen a goblin shark in real life before, but I saw a goblin shark in a book before and it looked like something out of my nightmares. Is anyone else here scared of goblin sharks, or is it just me?(5 votes)
- to be fair goblin sharks do get a bad wrap.they can get up to 450 years old how did you exspect them to look.plus coming from sience they used to be a normal salt water shark that lived in shallow water until a pregnet shark came down there and...you get the idea.but they did have to adapt to the harsh climate down there wich caused a ton of disfiguretion(1 vote)
- could it be more creatures in our oceanic part?(3 votes)
- yes weve only explored about 6% of the ocean and only 0.2% of the ,marieana trench(2 votes)
- I think that maybe we would find so many new things if we could explore the ocean floor but without water. That does make me woner though, what would we find?(3 votes)
- In2:38, the Narrator says the trench is 11 km deep. How deep is that when converted to miles?(2 votes)
- 6.83508 miles deep(5 votes)
- If the ocean's water disappeared for a day, wouldn't many species go extinct almost immediately?(2 votes)
- If all the oceans disappeared, it would create such a disturbance that the tectonic plates would probably go crazy causing world-wide earthquakes along with other devastating effects...!(4 votes)
- isnt it tectonic plates, not plate tectonics?(3 votes)
- isint the world one big country cuz there all connected by the ocean floor and all the country's just states [ joke question ](3 votes)
- Is there a reason we stopped exploring the ocean? I've heard three different scenarios that I can remember somewhat fully:
The first, being that it's obviously hard to get deeper in the ocean because of the pressure the deeper you get.
The second, being that we explored enough of it to assume what the rest of it would be like.
And lastly, something scary was down there.
Please tell me! I always think of the ocean and wonder why this is!(2 votes)- I'm pretty sure people are afraid of the ocean floor because they do not know enough about it and humans are scared of what they do not know. But also the theories about scary things being at the bottom of the ocean like the Kraken are usually from way back. I'm also pretty sure that the Kraken is really just a giant squid that some sailors saw some centuries ago. it might be kind of a let down for those who really wish that the Kraken and such creatures exist (which i get) but it really isn't all that practical.(2 votes)
Video transcript
- [Instructor] Imagine
that all the Earth's oceans disappeared for a day. And imagine that you being the
excellent Explorer you are, decided to go investigate. You'd travel across the continental shelf, down the continental slope
and across the abyssal plain. You'd see gaping trenches
running deep into the ground, and mountains taller than any
mountain on the continents. And you might wonder, what causes such dramatic
landscapes to be formed? Earth's lithosphere, which
is made up of the crust and the upper part of
the mantle, is broken up into large puzzle piece like
chunks called tectonic plates. These tectonic plates move around slowly over millions of years on
the section of the mantle below the lithosphere, which
we call the asthenosphere. There are two types of tectonic plates, oceanic plates and continental plates. The continental plates,
as you probably guessed, are the ones that make up the continents. The oceanic plates are the ones
that make up the sea floor. The main difference between oceanic plates and continental plates
is the type of crust found on each plate. Oceanic crust and continental crust are made out of different kinds of rock. The continental crust
contains a lot of granite, which is an igneous rock. This means that it was made out of rock that was once molten. The oceanic crust has
a lot of basalt in it, which is another kind of igneous rock. The difference in the kinds of rock that the crusts are made out
of means that the oceanic crust is denser than the continental crust. If you took a cubic centimeter of the rock from the continental crust,
it would be about 2.7 grams. A cubic centimeter from the oceanic crust, on the other hand, would
weigh about three grams. While this difference in density
might not seem like much, it completely changes how
tectonic plates interact. The high density of oceanic crust causes oceanic plates to
sink into the asthenosphere a bit more than continental plates do. When an oceanic plate
collides with another plate at a convergent boundary,
it always follows this rule, the denser plates always dives
beneath the less dense plate. When it's an oceanic plates and a continental plate converging, the denser oceanic plates
is the one that dips down. And when it's two oceanic
plates that are colliding, the older, denser oceanic
plate will move under the newer and less dense oceanic plates. And over time, the denser plate will be recycled into asthenosphere. The place where the plates collide is called a subduction zone. This bending of the denser plates under the other creates a trench. The deepest one is the Mariana Trench, which is located where the Pacific plates dives under the Marianna plates. The trench is about 11 kilometers deep. The plate that sinks into asthenosphere often has some water and
fluids trapped inside of it. These fluids heat up and
bubble to the surface. The hot fluids can cause
sections of mantle rock to melt into magma, which then rises to the surface and creates volcanoes. And you might be wondering,
if the sea floor is constantly being destroyed then what
keeps the earth from shrinking? Well, new sea floor is
constantly being created too. This happens when two
tectonic plates move away from each other at a divergent boundary. When two plates diverge
in the middle of an ocean, it creates a kind of
underwater mountain range called a mid-ocean ridge. As the plates move apart
at mid-ocean ridges, magma moves up, cools and forms
a new younger lithosphere. You can think of this process like a really slow conveyor belt. New ocean sea floor is made at the ridges, and moves away from them
over millions of years. This means that the oceanic crust that is closest to the
ridge is the youngest. And as it moves away from the ridge, the crust gets older and older. As it ages, the crust becomes
cooler and more dense. And eventually it dips back down into the asthenosphere at the trenches. The sea floor is perhaps the most unexplored part of our planet. So if they do drain the
ocean and you go for a walk at the bottom of the sea,
I hope you'll tell us all what it's like down there.