What do you think would happen if you started digging straight down into the Earth?
How deep do you think you could go? Would it be possible to dig all the way to the other side?
Well, some scientists in the Kola peninsula of Russia set out to answer that question.
They spent 20 years digging the Kola Superdeep Borehole and reached 40,230 feet deep into the
Earth. That's close to eight miles below the surface, and here's the thing. They only made
it 0.2 percent of the way through the planet. So why didn't they go deeper? To find out, we'll need
to explore the inside of the incredible planet beneath our feet. By the end of this lesson,
you'll be able to identify and describe the four main layers of the earth and explain the
factors that make exploring the Earth's inner layers such a challenge. Let's get started.
The Kola Superdeep Borehole only made it into the first layer of the Earth called the crust. This
is the layer we call home. The crust is made of a mixture of different kinds of solid rocks and
minerals. It's also the thinnest of Earth's layers by far. The continental crust, or the parts of the
crust beneath land masses, varies from about 25 to 50 miles thick. But the oceanic crust under
the oceans is as thin as three miles. Our planet's crust isn't just the layer we live on. It's also
the only layer we've actually explored at all. The Kola Superdeep Borehole made it less than halfway
through this layer. If it had kept digging deeper, the next layer it hit would have been the mantle.
The mantle is the layer that lies beneath Earth's crust. At a whopping 1,800 miles thick,
it's by far the thickest of our planet's layers. The mantle is made of rocks that are denser and
heavier than the rocks in the crust. Although these rocks are in the solid state of matter,
they actually flow like a very thick, slow-moving liquid. This movement is caused by the currents of
intense heat in the mantle. The outermost edges of the mantle are over 1,000 degrees Fahrenheit,
and the deeper you go, the hotter it gets. The innermost parts of the mantle are over
7,000 degrees, but that's not nearly as hot as our next layer, the outer core. The outer core
is about 1,400 miles thick, and it's mostly made of the metals iron and nickel. Now remember, the
deeper into the Earth we go, the hotter it gets. The outer core reaches temperatures as high as
9,000 degrees Fahrenheit. So how do you think these high temperatures impact the metals that
make up the outer core? Pause the video here and record your thoughts in your guided notes.
The scorching temperatures of the outer core are well
past the melting points of the metals found here.
As a result, the outer core isn't solid rock like the mantle and crust. Instead, it's made of molten
liquid metal. And there's one last layer that's even deeper: the inner core. The inner core is a
dense ball of iron about 750 miles across. It's close to 10,000 degrees Fahrenheit, making it as
hot as the surface of the sun. But despite being even hotter than the molten outer core, the inner
core isn't liquid. It's completely solid. What do you think is keeping the metal here from melting?
Remember, the inner core has an entire planet
pressing in on it. Even though it's definitely hot enough to melt iron,
the inner core stays solid because of the incredible amount of pressure it's under.
Our best efforts
to explore Earth's layers have barely scratched the surface of our planet. We've made it less than
halfway through the crust, and it doesn't look like we'll be getting much deeper anytime soon.
So what do you think it is that makes exploring the planet's inner layers
so challenging? Pause the video here and record your thoughts in your guided notes.
Firstly, reaching our planet's inner layers entails drilling through several thousand
miles of solid rock. But even if we can get through the rock, there's the problem of the
high temperatures. In fact, this is why the Kola Superdeep Borehole stopped at around 40,000 feet
down. The temperatures even a mere eight miles below the Earth's surface were just too much for
the drilling equipment to take. Plus, designing a drill that could withstand the incredible pressure
from all the rocks above pushing down was no easy task either. And remember, that's all
only halfway through the crust. Just imagine what trying to dig through the mantle would be like.
So with all of these challenges, how do earth scientists study our planet's inner layers?
Instead of digging down through thousands of miles of rock, earth scientists can use data from
earthquakes, rock formations, and even high-tech computer simulations to study the planet's layers.
That way, we can keep learning about the processes shaping the Earth's interior without needing to
plan for 10,000 degree temperatures. So let's recap what we learned today.
Now you know that the Earth's four main layers are the crust, the mantle, the outer core,
and the inner core, and that factors like extreme heat and pressure make it challenging
to explore the inner layers of our planet. Be sure to check out the practice questions
and extension activities that go with this lesson to learn even more about the layers
of our planet. And always remember, in earth science as in life, you rock. See you next time.
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