Download KEY______KEY_____KEY__ Earth`s Changing - Parkway C-2

KEY______KEY_____KEY__ Earth’s Changing Surface
• Section 2: “How Soil Forms” pp. 48 - 55 (Study Guide)
13.
soil is the loose, weathered material on Earth’s surface in which plants can grow.
14.
bedrock the solid layer of rock beneath the soil (bedrock gradually weathers to soil)
15.
Soil is a mixture of rock particles, minerals, decayed organic material, water, and air.
The weathered rock particles are made of
sand, silt and clay
16.
humus decayed organic material
17.
fertility how well the soil supports plant growth.
18.
Soil Particle Size:
clay = less than 1/256 mm,
Figure 7 (p 49)
sand = less than 2 mm,
19.
gravel = greater than 2 mm
loam soil that is made up of about equal parts of clay, sand and silt.
Fig 6 (p. 49) clay = 9 %, sand = 18%, silt = 18%,
air = 25%,
20.
silt = less than 1/16 mm,
water = 25%,
organic material = 6%
soil horizon layer of soil that differs in color and texture from the layers above and
below it.
21.
topsoil crumbly, dark brown soil that is a mixture of humus, clay and other minerals.
22.
subsoil clay and other particles that are washed down from the topsoil
23.
Figure 9 (p 51) Soils of North America
tundra soils thin soil with little humus (cold year-round)
northern forest range from think and fertile to thin with little humus (cool, wet climate)
prairie soils topsoil thick and rich in humus (cool, dry climate)
mountain topsoil usually thin because of cold temperature and heavy erosion
southern forest low in humus because of decay (warm wet climate)
desert thin soil low in humus (dry climate)
tropical low in humus and minerals (very wet and dry climate)
24.
litter loose layer of plant material like leaves and stems
25.
decomposers organisms (like bacteria and fungus) that break down the remains of
dead organisms into smaller pieces and digest them with chemicals.
26.
Some soil organisms make humus, the material that makes soil fertile.
Other soil organisms mix the soil and make spaces for air and water.
27.
Figure 10 (pp 52 - 53)
Every cubic meter of soil contains billions of
organisms. All organisms that live in the soil enrich humus with their wastes.
A Horizon topsoil: mixture of humus, clay and other minerals
B Horizon subsoil: clay and other particles that are washed down from the topsoil
C Horizon rock fragments from the bedrock
How do the following organisms help the soil?
plant roots break up the soil and hold it in place
insect larvae wastes make humus and burrowing breaks up soil
chipmunks burrows to make dens in soil, wastes make humus
mice burrow and makes nests in the soil, wastes make humus
snails feed on litter and contribute to humus
leaves, roots, and stems major source of humus
earthworms break up soil and make humus with wastes
ants colonies make tunnels and aerate soil
bacteria decomposer breaks down plant and animal remains
fungi decomposer breaks down plant and animal remains
28.
Why is it important to aerate the soil? plant roots and soil critters need oxygen and
water in the soil. Loose soil holds more air and water.