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Lesson 4
Earth’s Rocks and Soil
Main Idea
Rocks can be classified according to their composition and properties.
How are Rocks different and alike?
Rock- a naturally formed solid in the crust made up of 1 or more minerals
Ways to identify a rock
o name the minerals it has
o look for color, density or texture.
o Texture- size, shape and arrangement of mineral crystals
Rocks are grouped into three types according to how they are formed
o Igneous
o Sedimentary
o Metamorpic
Igneous Rocks- formed when melted rock materials cool and harden
o when lava is exposed to the air above ground it hardens and cools forming
igneous rocks
o lava- magma that reaches the surface
o when magma is below the ground it cools slowly and crystals take longer to
grow. This makes the crystals larger.
o when magma is above ground cooling is quicker. This makes the crystals
smaller.
Sedimentary Rocks- are made of small bits of matter
o Formed when sediments are pushed together. The weight from each layer of
sediments on top of each other squeezes them together to form the rock.
o Examples- halite, shale, siltstone, sandstone, conglomerate
How are sedimentary rocks useful?
o Sandstone- used for buildings
o Limestone- ground up to make concrete
o Bituminous- black coal
Contain fossils
o Fossils- the remains or imprints of living things of the past.
o Examples-footprints in soft mud, plants imprints in rocks
Metamorphic Rocks- a rock formed under heat and pressure from another kind of
rock
How does the rock change or form?
The original rock DOES NOT melt under the heat or pressure instead the mineral
grains in the original rock…
1. flattens and lines up
2. change with substances in surrounding mineral
3. separate into layers of different densities
In each case the result (final product) is DIFFERENT from the original.
How are Metamorphic Rocks used?

Slate- used for shingles (on roof tops) and stone walkways
o The minerals are tightly packed together so water does not get through
o Marble- used for statues, floors, countertops.
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The minerals have beautiful colors

Easy to carve
Where does soil come from?
o Solid rock crumbles into chunks  Chunks crumble into smaller pieces
living things die and decay into humus. All of this mixed together forms
soil.
o Humus- decaying plant or animal material
o Soil is different in every location you go to
o Soil has a mixture of many things
How can people ruin soil?
1. Pollution- harmful substances added to Earth’s land water or air
o People, factories, farms all ruin soil
o Garbage and hazardous waste is buried in soil
o Spraying chemicals to kill unwanted animals and plants
o Littering
2. Taking plants out of soil
When plants die and decay they add valuable substances back into the soil.
When plants are taken out of the soil, they can’t add the valuable substances
to the soil.
4. Letting cattle graze in the same area for a long time
5. Cutting down forests for lumber (wood)
How can people protect the soil?

Adding fertilizers and humus- replaces minerals removed by crops

Using crop rotation- growing different crops so the crop does not use the
same nutrients each time

Strip farming-strips of tightly growing grasses grow between crops that
are spaced apart. The grass trap runoff and the soil it carries.

Contour plowing- farmers plow across a slop instead of up and down.

Terracing- when a hillside is shaped into steps