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Name: ___________________________
Date: _____________________
Section: ____
Learning Strategies
Changing the Earth's Crust
By Cindy Grigg
The earth is very old. It has changed as time passed. The outer layer of the
earth is called the crust. The earth's crust is made of rocks and soil. Rocks
crumble and wear away. When rocks break down, they weather. Most rocks
weather very slowly over many years. Weathering happens in several different
ways.
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Freezing water weathers rock. When you look at a rock, you see many tiny cracks and
holes in it. When it rains or snows, water fills these holes and cracks. The water freezes and
pushes against the rock. The rock slowly breaks apart. Over many years, the water causes
rock to break into small pieces and form soil. You may have seen potholes in streets or roads.
A pothole forms when water freezes in cracks in the pavement. As the water freezes, it gets
bigger. It pushes against the cracks and makes a hole in the pavement.
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Plants also help to weather rocks. Soil can collect in the cracks of a rock. Plants can grow
in this soil. Then plant roots can break rocks apart. Over many years, the roots can help
crumble a large rock. Tree roots can break a boulder apart.
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Sometimes, rainwater and gases in the air can weather rocks. Carbon dioxide is a gas in
the air. It can mix with rain to form a new material that is an acid. This acid can make hard
minerals in rocks soft. Then the rocks slowly break apart. This type of weathering is called
chemical weathering. Rainwater can eat away the minerals in rocks. This can make hollow
spaces. Big hollow spaces in underground rocks are underground caverns called caves.
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Erosion changes the earth's crust, too. Erosion is the moving of soil and rocks by wind or
water. As rainwater runs down a hill or slope, it picks up some of the soil. The rushing water
carves out paths as it moves downhill. The soil is deposited at the bottom of the slope. If this
happens in a river, lake, or ocean, the soil makes the water dirty. Fish and other animals that
live in the water cannot breathe in the dirty water.
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Wind erosion moves many tons of soil each year. It forms sand dunes along a beach.
Plant roots can help stop wind erosion. Roots can hold the soil in place so that the wind does
not blow it away.
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Some animals such as earthworms live in the soil. Animals change the earth's crust as
they dig in the soil. Plants change the soil by helping to change rocks into soil. Plants can
stop or slow down erosion.
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People change the earth's crust, too. People dig rocks and soil out of the ground to build
roads and buildings. People cut down plants and trees. Then wind and water can easily erode
the soil.
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Most of these changes happen slowly over a long time. Some changes in the earth's crust
can happen quickly. An earthquake is a shaking or sliding of the earth's crust. Earthquakes
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happen when large blocks of rock in the crust suddenly move. Sometimes, the movement of
the rocks makes the land move up, down, or sideways. New cracks can appear in the earth's
crust.
A volcano is a mountain with an opening at the top. When a volcano erupts, melted rock,
ashes, and other materials burst out of the opening. Hot melted rock from inside the earth is
squeezed out of a volcano. Inside the earth, hot melted rock is called magma. When it comes
out of a volcano, it is called lava. When lava cools, it hardens into solid rock. The rock forms
new crust. Like earthquakes, volcanoes can change the earth's crust very quickly.
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Volcanoes can form new land. The Hawaiian Islands were formed by underwater
volcanoes. The islands are the tops of volcanoes in the Pacific Ocean. A new island is
forming today in Hawaii.
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Water, plants, and air help weather rocks. Water and wind help cause erosion of the soil.
People and animals change the earth's crust, too. Earthquakes and volcanoes can cause the
earth's crust to change very quickly.
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Copyright © 2008 edHelper
Changing the Earth's Crust
1. What things can change the earth's crust?
Earthquakes and volcanoes
Erosion and weathering
People and animals
All of the above
2. Which of these is not a cause of
weathering?
Plants
Animals
Water freezing
Chemicals in the air
3. The movement of soil or rocks by wind or 4. Rocks ___________ when they wear down or
water is:
Magma
Erosion
Weathering
5. The outer layer of the earth is called the:
Soil layer
Rock layer
Crust
7. What is an earthquake?
A shaking or sliding of the earth's
crust
A mountain with an opening at the
top
A slow way of changing the earth's
crust over many years
break apart over a long time.
Weather
Make chemicals
Make new rocks
6. Which of the following make quick changes to
the earth's crust?
Air and water
Erosion and weathering
Volcanoes and earthquakes
8. Water can mix with what gas in the air to form
an acid?
Oxygen
Carbon dioxide
Nitrogen