Journey to the Center of the Earth: Reading Comprehension

We all call the Earth home, but did you ever think about what our home is actually made
of? The planet is approximately 6,400 km from surface to center, but what makes up those
kilometers of Earth? If we could travel through the layers of the Earth, what would our trip
be like? In order to make this trip, we would need a special vehicle that could travel
through both liquid and solid rock and that could withstand intense temperature and
pressure changes! The deeper into the center of the Earth the hotter and it is and the more
pressure we will face.

In 1961 scientists drilled a hole 200 m into the oceanic crust. They hoped to reach the
Moho Discontinuity. Unfortunately, the project was canceled after Phase I. At this time, we
still do not have the technology needed to make it through the entire rocky layer of Earth,
let alone into deeper layers.

So how do scientists study Earth’s interior if we can’t get to through it? Seismologists are
geologists who study seismic waves to learn about Earth. Studying the behavior of
earthquake waves to gather data about Earth’s interior is similar to using sound waves to see
inside the human body. Observing seismic waves allows scientist to infer images of Earth’s
interior. Data has shown that seismic waves bend when they encounter sharp changes in
density. There are different kinds of seismic waves, known as P- waves (which can travel
through liquids and solids) and S-waves (which can only travel through solids).
Studying these waves help seismologists theorize the composition, thickness, density,
and phase of the four layers of the Earth.

Let’s start our journey to the center of the Earth! In order to make it through, we have to
start with the part of the Earth that we live on, the outermost rocky layer called the crust.
This layer can range from 5 to 40 kilometers thick, the thickest sections occurring at
mountain ranges and the thinnest sections part of the ocean floor. The crust is separated into
two parts- Oceanic crust (ocean floor) which consists mostly of dense rock such as basalt
and Continental Crust (dry land) which consists mostly of lighter and less dense rock such
as granite.

The continental crust is mainly made up of silicon, oxygen, aluminum, calcium, sodium, and
potassium. The thickness of the continental crust is mostly 35-40 kilometers. Continental
crust, found under land masses, is made of less dense rocks such as granite. The oceanic
crust is around 7-10 kilometers thick which its average thickness is 8 kilometers. It is found
under the ocean floor and is made of dense rocks such as basalt. The oceanic crust is heavier
than the continental crust.

We come to a boundary. Above this boundary the rocks of the crust, below a layer of the hot
rocks of the mantle. Together these form a rigid, rocky layer of Earth known as the
Lithosphere, which averages about 100 km thick. We continue into the mantle, where our
vehicle encounters a hotter, softer material that is under increasing pressure. This must be the
Asthenosphere- the soft, hot, plastic-like layer of the Earth that is constantly flowing slowly
 by convection currents. Pieces of the lithosphere float on top of the asthenosphere and another
solid layer of material lies below, making the mantle nearly 3,000 km thick. Its temperature is
about 300 –
800oC. The upper 150 kilometers of the asthenosphere has a temperature enough to facilitate a
small amount of melting, and make it capable to flow. This property of the asthenosphere
facilitates the movement of the lithospheric plates. The lithosphere, with the continents on top
of it, is being carried by the flowing asthenosphere

The attempt to study the Earth’s mantle extended as far as studying the rocks from volcanoes,
simply because they were formed in the mantle. Scientists also studied rocks from the ocean
floor. They have determined that the mantle is mostly made of the elements silicon, oxygen,
iron and magnesium. The lower part of the mantle consists of more iron than the upper part.
This explains that the lower mantle is denser than the upper portion. The temperature and the
pressure increase with depth. The high temperature and pressure in the mantle allows the solid
rock to flow slowly.

Finally, we’ve made it to the core! Phew, it’s SO hot down here! The core is subdivided into
two layers: the inner and the outer core. The outer core is 2900 kilometers below the Earth’s
surface. It is 2250 kilometers thick and is made up of iron and nickel. The temperature in the
outer core reaches up to 2000oC at this very high temperature, iron and nickel melt. The thick
core- a liquid outer core and a solid inner core. The iron and nickel material in both layers of
the core make up about 1/3 of Earth’s mass, but only about 15% of its volume. The core is just
slightly smaller than the moon. The molten metal outer core flows like a thick liquid, but there
is so much pressure on the atoms of the inner core that they are pressed together into a dense
ball of solid metal.
The outer core is mainly made up of iron and nickel moving around the solid inner core,
creating Earth’s magnetism. The inner core is made up of solid iron and nickel and has a radius
of 1300 kilometers. Its temperature reaches to about 5000oC. The extreme temperature could
have molten the iron and nickel but it is believed to have solidifed as a result of pressure
freezing, which is common to liquids subjected under tremendous pressure. We should
probably get out of here, before the enormous pressure and 5,000°C temperature turn our
vehicle into a solid ball too!

Questions:
1. Complete the chart below based on the information from “Journey
to the Center of the Earth.”

Crust Mantle Outer Core Inner Core

Thickness/Depth
State of Matter (S, L, G)

2. What happens to the temperature as we traveled closer to the center of the Earth?

3. What happens to the pressure as we traveled down?

4. What rocks make up most of the Earth’s crust?

b. Continental-

5. Why do you think the ocean crust contains rocks that are more dense than the rocks found on
land?

6. What makes up the lithosphere?

7. The plates of the lithosphere move slowly because they float on top of the asthenosphere.
Describe how the molten material in the mantle causes this movement of the lithospheric
plates.

8. What is so special about the outer core? Inner core?

9. Make a concept map on the interior of the Earth.