How Scientists Study the Interior of the Earth
We can't see what Earth's interior is made of, but scientists are able to study it in other
ways. In this video lesson you will learn how seismic activity helps us understand and
describe the inner layers of the Earth.
Earth Is Made Of Many Layers
Have you ever thought about digging a hole to China? It seems like a logical
way to get there instead of flying all the way around the globe. While this
sounds like a great idea, it would take you much longer to dig through the Earth
than to travel around it. Even if you could dig down that far, you would have a
difficult time getting through all of the stuff that lies underneath the surface of
the planet.
So if we can't dig that far, how do we know what makes up the interior of the
earth? Scientists are able to understand Earth's interior by studying seismic
waves. These are waves of energy that travel through Earth, and they move
similarly to other types of waves, like sound waves, light waves, and water
waves. Seismic waves are sent through the earth during earthquakes, and
those energy waves are what cause the ground to shake as they travel through
it.
Seismic waves are recorded by a machine called a seismograph, which tells
us about the strength and speed of the seismic waves. These recordings made
by a seismograph are called seismograms. Seismic waves travel at different
speeds when they pass through different types of material, so by studying
seismograms, scientists can learn a lot about Earth's internal structure.
Types Of Seismic Waves
Body waves are seismic waves that travel through Earth's interior, or its
'body.' Surface waves are seismic waves that travel through Earth's surface.
Makes sense, right?
Surface waves are important, but they don't provide much information about
what happens below the surface. For this, we need to study body waves so that
we can see what Earth's 'body' is like.
There are two types of body waves, called P waves and S waves. P stands for
primary waves because these waves travel the fastest and are detected first. S
stands for secondary wave because these are slower than P waves, arriving
second on the seismogram.
Earth's Interior
Since the information recorded on a seismogram tells us how fast body waves
are moving when they travel through Earth, we can tell what type of material
they're traveling through. As body waves travel through the Earth's internal
layers, their speed changes, causing the wave to 'bend.'
This bending is similar to looking at a straw in a half-full glass of water. If you
look at the straw from the side, it appears to 'bend' where it hits the surface of
the water. This is because the light waves are bending and slowing down as
they hit the different material, in this case the water. The same thing happens
to body waves when they travel through the Earth.
We know that the surface of the Earth is solid because we can easily see this.
But we need body waves to tell us what lies below. What they tell us is that
directly below the crust is a layer of rock with a different density. As we learned
in another lesson, this layer is called the mantle, and we know that it's a
different density than the crust because seismic waves 'bend' and suddenly
pick up speed where these two layers meet.
P waves can travel through both liquid and solid material, but S waves can only
travel through solids. Since both P waves and S waves travel through the
mantle, this means that it must be a layer of solid material. The really
interesting part about this 'solid' layer is that even though it is rock, it 'flows' like
a very thick liquid. It's similar to the consistency of silly putty, which if you punch
hard, feels like a solid, but if you stretch slowly, moves like a liquid.
Another pretty significant change occurs at about 1,900 miles down. S waves
suddenly stop as if they have hit a brick wall, and P waves 'bend' and slow
down so much that no waves are detected at the surface of Earth. What this
tells us is that there is another distinct change in density and composition here.
And in fact, this is the place where the mantle and the outer core meet. The
mantle is made of mostly that 'liquid' rock that moves like silly putty, but the
outer core is an area of mostly liquid iron, which is much denser than the rock
in the mantle. Since S waves can't travel through liquid, this is why they run into
a wall and stop. P waves can travel through it, but they do so much more slowly
than through solid material.
http://education-portal.com/academy/lesson/how-scientists-study-earths-interiorstructure.html#transcript
Name:________________________________________
Period:__________________
How Scientists Study the Interior of the Earth
1. How are scientists able to study the interior of the Earth?
2. Seismic waves are similar to ______________________________, ______________________________
and ______________________________ waves.
3. What are seismic waves sent through the Earth during what phenomenon?
4. Seismic waves are measure by an instrument called a ___________________________________
and give us information about the waves’ _______________________________ and
____________________________.
5. What type of waves travel through the Earth’s interior?
6. What type of waves travel through the Earth’s surface?
7. Name and describe the two types of body waves.
8. As body waves travel through the Earth’s layers, the waves ___________________ when
their speed changes, indicating a change in composition.
9. Which type of wave travels only through solids?
10. The outer core is mostly liquid iron. Which type of wave can travel through it?