Introduction to plate tectonics | Middle school Earth and space science | Khan Academy

Summary

This script explores the concept of plate tectonics, explaining how Earth's lithosphere is divided into tectonics plates that move over the asthenosphere. It describes the slow movement of these plates, which has reshaped Earth's continents from a single supercontinent, Pangea, to their current configuration. Evidence such as matching coastlines and shared fossils supports this theory. The script also details the three types of plate boundaries—convergent, divergent, and transform—and illustrates how these interactions shape geological features and cause earthquakes. The driving force behind plate movement is attributed to gravity acting on the denser plates over the more pliable asthenosphere.

Takeaways

• 🌏 The Earth's lithosphere, which includes the crust and upper mantle, is divided into tectonic plates that move over the asthenosphere.
• 🏁 Tectonic plates move at a very slow pace, only a few centimeters per year, similar to the growth rate of human fingernails.
• 🌌 The continents were once part of a supercontinent called Pangea, which broke apart over 200 million years ago to form the continents we know today.
• 🧩 Evidence for plate tectonics includes the jigsaw puzzle-like fit of continents' coastlines, such as the east coast of South America and the west coast of Africa.
• 🦕 Fossils of the same species found on different continents suggest that these land organisms lived when the continents were connected.
• 🚫 Tectonic plates move in various directions and interact at their edges in three main ways: convergent, divergent, or transform boundaries.
• 🏞️ Convergent boundaries, like the collision of the Indian and Eurasian plates, can create mountain ranges, such as the Himalayas.
• 🌋 Divergent boundaries occur where two plates move apart, potentially forming rift valleys and mid-ocean ridges.
• 🌀 Transform boundaries involve plates sliding past each other, leading to friction, pressure buildup, and earthquakes.
• 🌡️ The movement of tectonic plates is influenced by gravity, with the denser plates sinking into the asthenosphere at convergent boundaries.
• 🏔️ The Himalayan mountains continue to grow due to the ongoing collision of the Indian and Eurasian plates, adding over a centimeter each year.

Q & A

What is the Earth's lithosphere and what is its composition?

The Earth's lithosphere is the rigid outermost layer of the Earth, composed of the crust and the upper part of the mantle. It is broken up into tectonic plates that move on the asthenosphere.

How fast do tectonic plates move relative to each other?

Tectonic plates typically move only a few centimeters per year, which is comparable to the rate at which human fingernails grow.

What was the supercontinent that existed before the continents drifted apart to form the current layout of Earth?

The supercontinent that existed before the continents drifted apart is called Pangea.

What evidence supports the idea that continents were once connected as part of a supercontinent?

Evidence such as matching coastlines, fossils of the same species found on different continents, and the fit of the continents on a map like a jigsaw puzzle support the idea of continental drift and the existence of Pangea.

How do scientists categorize the interactions between tectonic plates at their edges?

Scientists categorize the interactions between tectonic plates as convergent, divergent, or transform boundaries based on how the plates move relative to each other.

What is a convergent boundary and how does it affect the Earth's surface?

A convergent boundary is where two plates come together, often resulting in the formation of mountain ranges, such as the Himalayas, due to the compression and uplift of the crust.

What is the significance of the Himalayan mountains in the context of plate tectonics?

The Himalayan mountains are significant because they are formed by the collision of the Indian tectonic plate with the Eurasian plate, demonstrating the ongoing process of plate tectonics.

What are divergent boundaries and what landforms can they create?

Divergent boundaries occur where two tectonic plates move apart, and they can create landforms such as rift valleys and mid-ocean ridges.

What is a transform boundary and how does it relate to earthquakes?

A transform boundary is where two plates slide past each other, causing friction and pressure buildup that, when released, can result in earthquakes.

What role does gravity play in the movement of tectonic plates?

Gravity plays a key role in the movement of tectonic plates, particularly at convergent boundaries where the edges of the plates can sink into the asthenosphere due to gravity.

How do the interactions of tectonic plates contribute to the changing landscape of Earth over millions of years?

The interactions of tectonic plates, through convergent, divergent, and transform boundaries, contribute to the formation and shifting of landforms, mountain ranges, and oceanic features, shaping the Earth's landscape over geological time.

Outlines

00:00

🌏 Earth's Dynamic Plate Tectonics

This paragraph introduces the concept of plate tectonics, explaining how the Earth's lithosphere, consisting of the crust and upper mantle, is divided into tectonic plates that move over the asthenosphere. It highlights the slow movement of these plates, which is comparable to the growth rate of human fingernails, yet significant over geological timescales. The paragraph also discusses the historical supercontinent of Pangea and how continents have drifted apart to form the current world map. Evidence supporting plate tectonics includes the fitting coastlines of continents and the presence of similar fossils across different continents, indicating a connected landmass in the past. The movement of plates is categorized into convergent, divergent, and transform boundaries, with examples provided for each type.

Keywords

💡Earth's lithosphere

The Earth's lithosphere is the rigid outer layer of the Earth, consisting of the crust and the uppermost part of the mantle. It is fundamental to understanding the video's theme as it is the layer where tectonic plates exist and move. The script mentions that the lithosphere is broken into tectonic plates that move on the asthenosphere, illustrating the concept of plate tectonics.

💡Tectonic plates

Tectonic plates are the pieces into which the lithosphere is divided. They are central to the video's theme as they are the primary agents of the Earth's surface movement. The script describes how these plates move slowly over the asthenosphere, causing the shifting of continents and the formation of various geological features.

💡Asthenosphere

The asthenosphere is a part of the Earth's mantle located just below the lithosphere. It is semi-solid and partially molten, allowing tectonic plates to move over it. The script explains that the asthenosphere's semi-fluid nature facilitates the movement of tectonic plates, which is key to understanding the dynamics of plate tectonics.

💡Pangea

Pangea refers to the supercontinent that existed during the late Paleozoic and early Mesozoic eras, where all of the Earth's continents were connected. The video uses Pangea as an example to illustrate the concept of continental drift, showing how the continents were once joined and have since separated into their current configurations.

💡Plate tectonics

Plate tectonics is the theory that describes the movement of Earth's lithosphere. It is the overarching theme of the video, explaining how the Earth's surface is in constant motion due to the shifting of tectonic plates. The script provides evidence and examples of how this theory is supported by the Earth's geological features.

💡Convergent boundaries

Convergent boundaries are areas where two tectonic plates move towards each other and collide. The script uses the collision of the Indian and Eurasian plates as an example, resulting in the formation of the Himalayan mountains, which demonstrates the significance of convergent boundaries in shaping the Earth's landscape.

💡Divergent boundaries

Divergent boundaries occur where two tectonic plates move away from each other. The video mentions that these boundaries can create rift valleys and mid-ocean ridges, showing how they contribute to the formation of new crust and the expansion of the Earth's surface.

💡Transform boundaries

Transform boundaries, also known as transform faults, are where two plates slide past each other horizontally. The script describes how this movement can cause earthquakes due to the friction and pressure buildup between the plates, highlighting the dynamic nature of the Earth's crust.

💡Fossils

Fossils are the preserved remains or traces of animals, plants, and other organisms from the past. The video uses the presence of the same species' fossils on different continents as evidence supporting plate tectonics, suggesting that these continents were once connected.

💡Coastlines

Matching coastlines between continents serve as evidence for the theory of plate tectonics. The script points out that the east coast of South America and the west coast of Africa have complementary shapes, implying that they were once part of the same landmass before the continents drifted apart.

💡Gravity

Gravity plays a key role in the movement of tectonic plates, particularly at convergent boundaries. The script explains that the denser crust of the subducting plate is pulled down by gravity into the asthenosphere, contributing to the formation of mountain ranges like the Himalayas.

Highlights

The Earth's lithosphere, including the crust and upper mantle, is broken into tectonic plates that move slowly over the asthenosphere.

Tectonic plates move only a few centimeters per year, similar to the growth rate of human fingernails.

Over millions of years, the movement of tectonic plates has significantly altered the Earth's continents, once all connected as the supercontinent Pangea.

The concept of Pangea suggests a time when one could travel from Africa to Antarctica or South America to Europe without crossing an ocean.

Scientists use evidence such as matching coastlines and shared fossils to support the theory of plate tectonics and continental drift.

The east coast of South America and the west coast of Africa have complementary coastlines, indicating they were once connected.

Fossils of the same species found on different continents suggest the landmasses were once joined before the plates drifted apart.

Tectonic plates interact through convergent, divergent, and transform boundaries, shaping the Earth's geological features.

Convergent boundaries, where plates come together, can create mountain ranges like the Himalayas, which continue to grow.

The Indian plate's collision with the Eurasian plate is an example of a convergent boundary, with the Himalayas growing over a centimeter each year.

Divergent boundaries occur when plates move apart, potentially forming rift valleys and mid-ocean ridges.

Transform boundaries or faults happen when plates slide past each other, causing friction and periodic earthquakes.

The movement of tectonic plates is influenced by gravity, with denser plates sinking into the asthenosphere at convergent boundaries.

While tectonic plates move slowly, their movement over geological time scales has a profound impact on Earth's landscape.

The Earth's internal heat may play a role in plate movement, but gravity is considered the key driving force.

Tectonic plates' solid and dense nature allows them to rest on the asthenosphere, which behaves like clay under the influence of gravity.

Transcripts

- [Narrator] What if I told you

that the earth below you is moving?

You'd probably say, "Of course it's moving.

We're standing on a planet

that's spinning on its axis

while revolving around the Sun

at about 107,000 kilometers per hour.

And on top of that,

our whole solar system is circling the center

of the Milky Way galaxy."

But there's another kind of movement that happens slowly

in the rock beneath your feet.

Earth's lithosphere, which is made up of the crust

and the upper part of the mantle,

is broken up into pieces called tectonic plates.

These plates move around on top of the asthenosphere,

which is the section of the mantle

just below the lithosphere.

Don't bother racing a tectonic plate,

because your victory would be guaranteed.

Tectonic plates typically only move

a few centimeters in a year,

which is about as fast as your fingernails grow.

However, after millions of years, those distances add up.

This means that the Earth hasn't always

looked the way it does now.

Scientists believe that the continents were once

all connected in one big supercontinent called Pangea.

Just imagine if the continents were still connected today.

You could drive from Africa to Antarctica

or even take a train from South America to Europe.

Over 200 million years, Pangea broke apart,

and the pieces drifted into the continents we know today.

So if the plates move so slowly,

how do we know that they move at all?

Scientists have documented evidence

from various features on Earth

that support the theory of plate tectonics.

If you cut out the continents on a map, you could see

that they almost fit together like a jigsaw puzzle.

For example, the east coast of South America looks

like it could fit into the west coast of Africa.

Matching or complementary coastlines

is one piece of evidence

that continents were once in different locations.

Another piece of evidence

is that scientists have found fossils

from the same species on different continents.

There's no way those land organisms

could've traveled across the ocean.

This suggests that the animals lived

when the continents were connected.

And the plates are still moving,

slowly but surely, to this day.

But they aren't all moving in the same direction.

A plate can collide with one plate,

move away from a different plate, and slide past another.

We categorize the ways plates interact at their edges

as having convergent, divergent, or transform boundaries.

Con is a Latin prefix meaning together,

so convergent plate boundaries are places

where two plates come together.

Let's take a look at an example of a convergent boundary

where the Indian tectonic plate collides

with the Eurasian plate.

The crust of the plate becomes compressed,

and the Indian tectonic plate gradually moves

under the Eurasian plate.

However, the lower density of the crust

keeps the Indian plate from sinking back

into the asthenosphere all the way.

This lifts up the Eurasian plate

and creates the Himalayan mountains.

These mountains are some of the highest in the world,

and they include Mount Everest,

which is the tallest mountain above sea level.

And the two plates are still colliding.

This causes the Himalayas to grow

by more than one centimeter each year.

Another kind of plate movement

is called a divergent boundary.

The di in divergent comes

from a Latin prefix meaning apart,

so divergent boundaries happen

where two tectonic plates move apart.

Divergent boundaries can create different kinds

of land forms, like rift valleys and mid-ocean ridges.

The third kind of plate boundary

is called a transform boundary or transform fault,

and it happens when two plates slide past each other.

Okay, maybe slide isn't the best word for it,

because the plates don't move in one continuous motion.

You can imagine when two incredibly large,

bulky, rocky things move past each other,

there's a lot of friction.

Pressure builds up between the plates,

and once it gets to be too much,

the plates slip and release the pressure.

This motion causes earthquakes.

And you might be wondering, what causes plates to move?

Well, scientists are always learning about the Earth,

since the Earth is so complex.

Although Earth's internal heat may play a small role,

more evidence shows that gravity is key.

Tectonic plates are solid,

and they're denser and cooler than the asthenosphere.

Because the asthenosphere is also pretty solid,

the plates rest on top of it.

However, the asthenosphere is so hot

that it can behave a bit like clay.

This means that at convergent boundaries,

the edges of the plates can sink into the asthenosphere,

a process that is driven by gravity.

So even though you'd win in a race against a tectonic plate,

the plate will still keep on moving millions of years

after you've declared yourself to be the winner.