Science Chapter 5: Rocks, Soil and Change
Lesson 1:
rock: a natural solid, nonliving material made of one or more minerals.
mineral: a natural material that forms from nonliving matter.
igneous rock: rock that forms when melted rock cools and hardens. Sometimes it
cools quickly above the ground and the mineral gains are small (obsidian).
When it cools slowly below the ground the mineral grains are large (granite).
sedimentary rock: rock thatforms in layers from sediments. Sediments are tiny
bits of rock, shells and other materials that settle in rivers, lakes and oceans.
Over thousands of years the sediments are pressed together and cemented into
a layer of rock. (limestone, shale)
metamorphic rock: rock that has been changed into a different type of rock by heat
and pressure underground. (granite gneiss [nīs] ; shale slate)
Lesson 2:
soil: the layer of loose material that covers most of Earth’s land. All soil has the same
four substances: tiny pieces of rock called particles, air, water and humus.
humus: the decayed remains of plants and animals that were once alive. As these
remains rot they release nutrients into the soil. A nutrient is a substance
needed by living things for energy and growth.
Soil layers: 1) topsoil: top layer with the most humus
2) subsoil: under topsoil, lighter in color, includes pieces of broken rock
and tree roots.
3) bedrock: rock layerbelow subsoil, as this rock breaks down it
provides resources for making new soil.
Kinds of soil: 1) sand: large rock particles, feels gritty, water passes through quickly
2) silt: medium-sized particles, feels slippery and smooth when wet.
Holds water better than sand.
3) clay: small particles, feels smooth and sticky when wet. Holds
water so well that roots of plants may “drown”’ if they can’t get air.
loam: a mixture of sand silt and clay. It also contains air, water and humus.
Lesson 3:
weathering: any process that breaks down rocks into smaller pieces. This is usually a
slow process that goes on all the time. Physical forces, chemicals and
biological processes can all cause weathering.
Plants can sometimes cause weathering when their roots grow into cracks in
rocks. As the roots get bigger, they split and break up the rocks. Some
plants can release chemicals that weaken rocks.
Water can cause weathering by changing the minerals in the rocks, making
them weak. Water can also cause weathering as it freezes and thaws in
cracks in the rocks.
erosion: the movement of the weathered material away from the area
Water and windare major causes of erosion.
Rainwater can carry away the soil in bare fields and hillsides. Waves cause
erosion along the shorelines. Rivers carry soil and rocks along in their current.
Erosion by wind is common in dry regions. Few tall plants grow in deserts so
there is little to stop the particles from blowing to other places.
Sand and soil particles can cause weathering and erosion when blown by the
wind. They hit the rocks and break off tiny grains. This makes the rocks
slowly change shape.
Lesson 4:
extinct: plants and animals that are no longer living on Earth.
fossil: the hardened remains or marks of a living thing from long ago, often found in
sedimentary rock. Fossils help us learn about plants and animals that are
extinct, and about how environments have changed.