Weathering, erosion, and Earth's features (grade 4)

Erosion moves bits of rock and soil. Running water is the biggest mover. After a big rain, soil washes down a hill.

Over a very long time, a river can carry away so much rock that it cuts a deep valley.

We can slow erosion. Plant roots hold soil in place. Low walls or steps on a hill slow down running water.

Rock forms in layers, like a stack of pancakes. New layers go on top.

So the bottom layer is usually the oldest. The top layer is the newest.

Fossils in a layer show what the place was like then. Sea shells mean an ocean. Ferns mean land with plants.

Earth's outer layer is cracked into huge pieces called plates. The plates move very slowly.

Where plates rub or push on each other, there are many earthquakes and volcanoes. On a map, they make long lines along the plate edges.

We can't stop earthquakes. But engineers can build frames that bend and sway. A building that can bend is less likely to crack and fall.

We use energy sources to make electricity and run cars.

Sun, wind, and moving water keep coming back. They are renewable. They will not run out.

Coal, oil, and natural gas took millions of years to form. We use them much faster. They can run out.

Using coal has costs. Mines can harm the land. Burning coal puts smoke and gases into the air.