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6.10A: Layers of Earth
Earth and Space
The Layers of Earth
Lexile 660L
1 Earth's surface is covered with water and land. Have you
ever wondered what is deep inside our planet? Earth is full
of surprises. You could cut a section out of the planet. It
would show three distinct layers: the crust, mantle, and core.
2 The first layer is called the crust. This is the surface we live
on. The continents and the ocean basins make up the crust.
It is Earth's thinnest layer. It is 35-70 km thick under the
continents. The crust is only 5-10 km thick under the oceans.
3 Earth's outer layers are the crust and the mantle that lies below it. These are less dense than
the core. Both the crust and the mantle are made mostly of silicates. Silicates are minerals rich
in the elements oxygen and silicon. The core contains the dense elements iron and nickel.
Earth's layers formed as the planet cooled and became solid. As Earth cooled, the less dense
elements rose to the surface. They separated into the crust and mantle layers around the inner,
dense core.
4 Going down through Earth's layers, temperature and pressure increase. This is due to the
mass of the layers of rock. The mantle is the second of Earth's layers. Most of the upper
portion of the mantle is made of solid rock like the crust. Some of the upper mantle is semimolten. It is able to flow. It is like thick, gooey syrup. This allows the rigid, crustal plates
resting on the upper mantle to float. Even though we can't feel it, the plates are slowly moving
all of the time. The mantle stretches down into Earth for 2,900 km. The lower mantle is solid
because of the great pressure placed on it.
5 In the center of Earth is the core, divided into two parts: the inner and outer core. These are
made of iron and nickel. The entire core is very hot. It is not surprising that the outer core is in
a molten state. However, the inner core is solid. This seems impossible, but the inner core is
kept solid by the intense pressure of all the layers above it. It has a diameter of 2,400 km. It is
surrounded by the outer core, which is about 2,300 kilometers thick. The inner core plays an
important role in the process that generates Earth's magnetic field.
6 Earth's three layers make our planet unique in the solar system. The crust, mantle, and core
are all distinct. They vary in composition, temperature, pressure, and state of matter. The solid
metal center is surrounded by a liquid core. These are covered by a sea of soft putty-like rock
mantle. They are topped with a solid, rock crust. There is no planet like Earth in the entire
solar system.
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6.10A: Layers of Earth
Earth and Space
1
2
3
What is the correct order of the layers of Earth, starting deep in the
center?
A
Inner core, outer core, mantle, crust
B
Crust, mantle, outer core, inner core
C
Mantle, outer core, crust, inner core
D
Outer core, inner core, crust, mantle
Which statement best describes the crust?
A
The crust is divided into sections and made of some of the densest
rocks found in Earth.
B
It is the outermost layer of Earth, composed of solid rock, and divided
into sections called plates.
C
The crust is made out of solid nickel and iron.
D
The crust is made of molten rock that flows like a thick, gooey syrup.
The core of Earth is made out of iron and nickel. The outer core's
temperature is so hot that it melts the metal. The inner core is solid metal.
What causes these differences?
A
The outer core is 2,300 km thick.
B
The inner core is kept solid by the intense pressure of all of the layers
above it.
C
The inner core has a cooler temperature allowing the metal to remain
solid.
D
The inner core is made of a different metal.
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6.10A: Layers of Earth
Earth and Space
4
This layer of Earth is divided into two sections, both of which primarily
contain silicate minerals. Part of one of the sections is able to flow like a
thick fluid. What is this layer known as?
A
Outer core
B
Mantle
C
Inner core
D Crust
5
Complete the following analogy:
Earth's inner core:_____ as Earth's outer core:mantle
A
magnetic
B
atmospheric
C
solid
D
thermal
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