Students know some changes in
the earth are due to slow processes, such as
erosion, and some changes are due to rapid
processes, such as landslides, volcanic
eruptions, and earthquakes.
Students know natural
processes, including freezing and thawing
and the growth of roots, cause rocks to
break down into smaller pieces.
Students know moving water
erodes landforms, reshaping the land by
taking it away from some places and
depositing it as pebbles, sand, silt, and
mud in other places (weathering, transport,
1. Changes in the Earth
You may not realize
it, but the Earth is always changing. New mountains, lakes and
rivers are being made, and old ones are disappearing. Sometimes
the changes are fast, and sometimes the changes are slow. We are
going to learn about things that slowly change the Earth. This
gradual change is caused by erosion
2. What is erosion and weathering?
when rocks are broken into smaller pieces. These smaller pieces
called sediment, sand, pebbles or
smaller pieces are moved by wind or water it is called
erosion. So, weathering is making
smaller pieces and erosion is moving the pieces.
sediment, mud, sand, pebbles or
silt from one place to another
Think about a pile
of dirt. If a strong wind blows, what happens to the dirt?
If the wind keeps
blowing long enough and hard enough, the whole pile will
erode, or wear
A mountain is like a
big pile of dirt. The wind blowing across a mountain will slowly
move the dirt and rocks and the mountain will become shorter and shorter
until it is flat.
Wind can make some interesting shapes.
same pile of dirt. You can also move the dirt by using water.
Think about your garden hose. If you have a pile of dirt on the
patio or sidewalk, you can use the water to wash it away.
The same thing
happens with big mountains.
If you let the water run in the middle of the dirt pile, it would start to carve out a
little stream. The water would continue to move more dirt from the
stream and the stream would get wider and deeper. Water is a very
powerful force. Given enough time, a river can carve through rocks
like a knife carves through meat.
Waves crashing against rocks can
reshape the rocks
Which of these would most affect the
amount of sediment a river can carry?
the color and shape of the sediments the temperature and amount of
salt in the water the size and speed of the
How can you break a rock?
break rocks, even really BIG rocks through
weathering. Think about a sidewalk, which is like a rock.
You've seen cracks in sidewalks. Sometimes plants grow in the
cracks. As the plants grow, they cause the crack to get bigger.
Another thing that
can cause the crack to get bigger is ice. When it rains, water
gets into cracks. If the water freezes it becomes ice.
The ice pushes the crack open, and over time the crack will
cause the rock to break apart.