Earth’s Layers Paragraph
It might seem like the Earth is made up of one giant solid piece of rock but actually, that’s not true.
In fact some layers of the Earth are actually moving! After many years of studying the earth and realizing
that the layers are moving, scientists have also realized that the Earth is made up of three main layers.
Before we can study the layers though we need to understand how scientists have come to understand what
the Earth is made up of.
Scientists have been performing two types of experiments for many years in order to discover what
the Earth is made up of. First, scientists have what is called direct evidence. This type of evidence is
evidence that scientists can directly see. Scientists collect direct evidence by researching landscapes,
caves and drilling rock samples. There are scientists whose job is just to collect direct evidence. Knowing
that, how far do you think scientists have been able to reach? 100 miles, 300 miles, 1,00 miles beneath
Earth’s surface? Guess again. While direct evidence has been collected for many years, scientists have
only been able to reach depth up to 12 km or 7.4 miles. Second, scientists have what is called indirect
evidence. This type of research is done with data collected from seismic waves, or vibrations that travel
through the Earth that carry the energy released from an Earthquake.
Seismic waves are important
because the speed of seismic waves lets scientists know if they are moving through a liquid or a solid. We’ll
be able to better understand how seismic waves travel through liquids and solids after our earthquake unit.
Besides performing experiments where they collect direct and indirect evidence, scientists also
know a lot about the temperature of the Earth. As you travel towards the center of the Earth the
temperature increases, meaning it gets much hotter. Scientists have been able to determine that this heat
is leftover from when the Earth formed and also comes radioactive elements that are decaying, or breaking
down.
Not only does the temperature increase as you travel towards the center of the Earth but the
pressure also increases as well. That means that as you travel towards the center of the Earth there is
more pressure. You’ve experienced something similar to this if you’ve ever swam to the bottom of a
swimming pool or a lake. As you swim towards the bottom of a pool or a lake, you can feel the pressure
change and you can feel it in your ears. Pressure is important in understanding how the Earth works but it’s
also important to understand the different layers of the earth as well. If we were to divide the Earth into
three main layers those layers would be the crust, mantle and the core. These layers actually get further
divided beyond just three main layers.
Let’s start with the crust. This is the layer of the Earth that is made up of solid rock that includes
both dry land and the ocean floor. The crust is anywhere from 6-70 km (or 3-43 miles) thick. When
talking about the thickness scientists have found that in most places the crust in 6-40 km thick, but can be
up to 70 km thick beneath mountains. While thickness is important you probably want to know what you can
find as part of the crust. The crust is where we find rocks, soil and water. There is also something
interesting about the crust: there are actually two types of crust! The first is oceanic and as you might
have guessed, we find this beneath the oceans. It’s made up of basalt which is a very dense rock
(remember what we learned about density?). The other type of crust is continental crust. This crust as
you guessed it, forms the continents and is made up of mainly granite. Granite pretty much has opposite
characteristics of basalt meaning granite has a light color and is less dense.
The second main layer of the Earth is the mantle. The mantle is a layer of solid material found
between the crust and the outer core. This layer of the Earth has a thickness of 2,900 km (1,801 miles).
The mantle is actually divided into two parts as well. The first layer is the lithosphere. This is the upper
most part of the mantle and also includes part of the crust making it about 100 km (about 62 miles) thick.
The thickness does not give the lithosphere its name the name actually comes from the word ‘litho’ which
means stone. It makes sense for this layer to be named after stone because that explains the rigid rock of
the lithosphere. When scientists explain the lithosphere as rigid, it means that it’s not flexible and can’t
move.
Below the lithosphere is the asthenosphere. This is part of the upper mantel is softer and can bend
and move very slowly which gives it something scientists call ‘plasticity.’ The asthenosphere is solid, but has
that plasticity we just talked about. Let’s explain what plasticity is. Have you ever taken your foot and
pushed on blacktop on a hot summer day? Good, you have done this experiment with black top which means
you’ll understand plasticity perfectly. If you were to kick that blacktop, you would stub your toe. If you
slowly take your foot and apply pressure to that blacktop you can get it to move on a very hot summer day.
The asthenosphere acts the same way, with enough pressure, heat (and we already know pressure and
temperature increase as you go towards the center of the Earth) and time, the asthenosphere moves but
very slowly.
The last part of the mantle is the lower mantle. This section is located below the asthenosphere.
Besides being located below the asthenosphere the only other characteristic of it is that it extends to the
core.
Well we’ve made it to the last layer of the Earth, the core. As you might have guessed the core is
also further divided but it is only divided into two layers. The first layer is the outer core which is a layer
of molten metal. Molten metal, what’s that? This is metal that is liquefied by heat (remember we’re
getting hotter as we move towards the center of the Earth). That’s right, it’s so hot in this layer that it’s
actually liquid and has a thickness of 2,300 km (1,429 miles). These liquid metals are iron and nickel. Next,
we have the inner core. This layer is solid. Wait, this layer is solid even though it’s so hot? Yes,
temperature increases but remember pressure increases too. So because there is so much pressure this
layer is actually solid, even though it is the hottest. Although we know this is the hottest layer, scientists
aren’t quite sure what it’s made up of but they’re pretty sure it’s made up of iron and nickel. After learning
all this information about the inner core the last thing we need to know is the thickness of the inner core.
It’s 1,200 km thick which is equal to 745 miles.
Wow, we’ve learned a lot today about the layers of the Earth! Maybe you learned that the Earth
isn’t actually made up of solid rock and that it isn’t just one layer in fact, there are many layers. Those
layers are important for understanding how the Earth works and why we see formations like mountains,
volcanoes and experience earthquakes. All of the research that was completed by scientists has brought us
to the information we now know today as they continue their research who knows how much more we’ll learn
about the Earth and its layers.