Name:
Objective: I can explain Earth’s three chemical
layers.
Date:
Homeroom:
Handout #: 1.1
DO NOW
Answer in complete sentences.
1. Why is science important?
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2. Based on this weekend’s homework assignment, what are the layers of Earth?
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3. What is the thinnest layer?
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4. What do you think is the deepest layer humans have drilled into?
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Objective: I can explain Earth’s three chemical layers.
Inside the Earth
If you tried to dig to the center of the Earth, what do you think you would find? Would
Earth be solid or hollow? Would it be made of the same material throughout?
The Composition of the Earth
Billions of years ago, the Earth started out as a hot, gooey ball of rock. The heaviest
material, mostly iron and nickel, sank to the center of the Earth and became the core.
The surface of the Earth slowly cooled off and hardened. These surface rocks became
the crust.
The Earth is divided into three chemical layers—the crust, the mantle, and the core—
based on the compounds that make up each layer. A compound is a substance
composed of two or more elements. The less dense compounds make up the crust and
mantle, and the densest compounds make up the core.
1. Why do you think the densest compounds are found in the core?
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The Crust
The outermost layer of the Earth is the crust, which is the thinnest layer. Its thickness
varies from 5 to 100 km thick.
There are two types of crust—continental and oceanic. Both continental and oceanic crust
are made mainly of the elements oxygen, silicon, and aluminum. However, the denser
oceanic crust has almost twice as much iron, calcium, and magnesium, which form
minerals that are denser than those in the continental crust.
Shoulder partners: compare and contrast oceanic and continental crust. How are they
similar? How are they different?
The Mantle
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The layer of the Earth between the crust and the core is the mantle. The mantle is
much thicker than the crust (1% of Earth’s mass) and contains most of the Earth’s mass
(67%). It is composed mostly of oxygen, magnesium, silicon, and iron.
No one has ever visited the mantle. The crust is too thick to drill through to reach the
mantle. Scientists must draw conclusions about the composition and other physical
properties of the mantle from observations made on Earth’s surface. In some places,
mantle rock pushes to the surface, which allows scientists to study the rock directly.
2. In what areas of Earth’s surface do you think mantle rock is pushed to the surface?
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Scientists also look for clues about the mantle on the ocean floor. Magma from the
mantle flows out of active volcanoes on the ocean floor. These underwater volcanoes
have given scientists many clues about the composition of the mantle. The mantle is
denser than the crust, because it has more magnesium and less aluminum and silicon
than the crust.
Video clip: underwater lava flow.
Material in the mantle moves due to
convection currents within the mantle. The
Earth releases internal heat through
convection. Hot material rises to the
surfaces and spreads out, while material at
the surface cools and sinks back to the
middle of the mantle.
What is convection?
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What are three differences between the crust and mantle?
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The Core
The core extends from below the mantle to the center of the Earth. Scientists think that
the Earth’s core is made mostly of iron and contains some nickel but almost no oxygen,
silicone, aluminum, or magnesium. The core makes up approximately one-third of the
Earth’s mass. The core is separated into two layers: the inner core and the outer core.
3. Is the core denser or less dense than the mantle? How do you know?
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4. Which layer is under the most pressure? Why?
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Twig video – structure of the Earth
How do scientists know about Earth’s interior?
How do scientists know things about the deepest parts of the Earth, where no one has
ever been? Scientists have never even drilled through the crust, which is only a thin
skin on the surface of the Earth. So, how do we know so much about the mantle and
the core?
Would you be surprised to know that some of the answers come from earthquakes?
When an earthquake happens, vibrations called seismic waves are produced. Seismic
waves travel at different speeds through the Earth. Their speed depends on the density
and composition of material that they pass through. For example, a seismic wave
traveling through a solid will go faster than a seismic wave traveling through a liquid.
When an earthquake happens, machines called seismographs measure the times at
which seismic waves arrive at different distances from an earthquake. Seismologists can
then use these distances and travel times to calculate the density and thickness of each
physical layer of the Earth. The figure below shows how seismic waves travel through
the Earth.
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5. What are seismic waves?
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6. What affects the speed of seismic waves after an earthquake?
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