Fremont Magnet Elementary

Slow Changes on the Earth

Standards:

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, and deposition).

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 and weathering.

2. What is erosion and weathering?

Weathering happens when rocks are broken into smaller pieces. These smaller pieces are called sediment, sand, pebbles or silt.
When the smaller pieces are moved by wind or water it is called erosion. So, weathering is making smaller pieces and erosion is moving the pieces.

By moving sediment, mud, sand, pebbles or silt from one place to another erosion creates...


floodplains	deltas

sandbars	beaches

Watch a brainpop movie about erosion

3. Wind

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 away.

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.

Sunset on Delicate Arch, Arches National Park

4. Water

Imagine that 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.

The North Kaibab valley with the Grand Canyon of Colorado at the bottom

Waves crashing against rocks can reshape the rocks

Click here to see an animation of river water moving sediment.

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 river

5. How can you break a rock?

You can 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.

Which type of rock would weather faster?

oddly shaped rock
smooth rock
cracked rock

Watch a brainpop movie about weathering

How do you think these formations were made?

fast moving water
moving air and sand
ocean tides

Sunflowers in the Black Hills, facing Devil's Tower Wavy sand formations, Zion photographs from http://www.gdargaud.net/Photo/Themes.html

National Geographic Oct 2006

http://www.phschool.com/atschool/sci_exp_lep/earth_science/Student_Area/ES_SC8_ACT_index.html

Back to 4th Grade Science