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LIVING IN THE ENVIRONMENT, 18e
G. TYLER MILLER • SCOTT E. SPOOLMAN
Rocks and Soil
©©Cengage
CengageLearning
Learning2015
2015
What Are Minerals and Rocks?
• Mineral
– Naturally occurring compound that exists as a
crystalline solid
• Mineral resource
– Concentration that we can extract and
process into raw materials
• Rock
– Solid combination of one or more minerals
© Cengage Learning 2015
What Are Minerals and Rocks?
• Sedimentary rock
– Made of sediments
• Dead plant/animal remains
(fossils!)
• Tiny particles of weathered and
eroded rocks
– The sediment gets turned into rock by
• Being buried/compacted by weight
or rocks
• Being cemented together by
materials that have been dissolved
in water
© Cengage Learning 2015
What Are Minerals and Rocks?
• Metamorphic rock
– Existing rock
subjected to high
temperatures,
pressures, fluids, or a
combination
– Pressure and heat can
come from being
buried deep in the
earth or from proximity
to magma
© Cengage Learning 2015
• Igneous rock
– Intense heat and
pressure, magma
wells up from the
earth’s mantle, cools &
hardens
Examples of Igneous Rocks
• Pumice
• Obsidian
• Basalt
• Other examples
include: Diabase,
Diorite, Gabbro,
Granite, Rhyolite,
Scoria
© Cengage Learning 2015
Examples of Sedimentary Rocks
• Shale = silt particles
• Sandstone = sand
particles
• Limestone = calcium
carbonate or calcite
(shells of marine
organisms)
• Other examples
include: Breccia,
Conglomerate
© Cengage Learning 2015
Examples of Metamorphic Rocks
• Marble
• Slate
• Gneiss
• Other examples
include: Quartzite,
Schist, Serpentinite
© Cengage Learning 2015
Earth’s Rocks Are Recycled Very Slowly
• Rock cycle
– Rocks are recycled
over millions of
years
– Erosion, melting,
and metamorphism
– Slowest of earth’s
cycle processes
© Cengage Learning 2015
External Earth’s Processes: Can Lead to
Soil
• Weathering-breakdown of solid rock
– Mechanical (Physical) weathering
• Frost Wedging, freeze-thaw cycle
– Chemical Weathering
• Oxidation (losing/gaining e-)
• Hydrolysis (splitting of water)
• Erosion-process by which earth particles are moved from
one place & deposited in another
– Wind
-Ice
– Water
-Gravity
© Cengage Learning 2015
Soil is the Foundation of Life on Land
• Mixture of eroded
rock, mineral
nutrients, decaying
organic matter,
water, air, humus
(microorganisms,
decaying organic
material) & living
organisms
© Cengage Learning 2015
• Formation begins
when
– Bedrock is slowly
broken into
fragments/particles
by physical,
chemical &
biological
processes
Soil is the Foundation of Life on Land
• Key component of
earth’s natural
capital
• Supplies most of
nutrients needed
for plant growth
• Purifies & stores
water
• Organisms living in
it remove CO2 from
atmosphere &
store it as organic
carbon compounds
– Helps control
earth’s climate
© Cengage Learning 2015
Mature Soils
• Contain horizontal
layers “horizons”
• O horizon
• A horizon
• B horizon
• C horizon
• Bedrock (base
parent material)
© Cengage Learning 2015
The Horizons of Soil
• “O horizon”
– Leaf litter
• “A horizon”
– topsoil
– Upper layer
• Contain bacteria, fungi,
earthworms, small insects
• Decomposers break down
compounds into “humus”
& inorganic materials
© Cengage Learning 2015
The Horizons of Soil
• “B Horizon”
– subsoil
• “C horizon”
– Parent material
• Most of inorganic matterbroken down rock containing
varying mixtures of sand, silt,
clay, gravel
• Underneath “C” is the
bedrock
© Cengage Learning 2015
The Horizons of Soil
• Spaces (“pores”) contain air or water
• As long as “O/A” are anchored by vegetation,
the soil layers as a whole act as a sponge,
storing water & nutrients!
• Topsoil-renewable resource but very slow
replenishment rate! (1 cm takes 100s of years to
form!)
© Cengage Learning 2015
Soil Properties
1. Water
2. Texture: the way the soil
feels
– Infiltration
– Leaching
– Porosity: amount of
pore spaces
– Permeability: ability to
transmit fluids
Water
Water
− Depends on amount of
each sized particlestermed soil fraction
− Sand: larges, gritty
− Silt: medium, soft,
silky, floury
− Clay: small, sticky,
hard to squeeze,
greatest surface area
High permeability
© Cengage Learning 2015
Low permeability
Soil Properties
100%clay
0
80
clay
60
Increasing
percentage clay
san
dy
clay
sandy clay
loam
40
loamy
sand sand
clay
loam
loam
sandy
loam
Increasing
percentage silt
silty
clay
40
20
20
60
silty clay
loam
silty
loam
0
100%sand
80
60
40
20
© Cengage Learning 2015
Increasing percentage sand
80
silt
100%silt
Gravel
2-64 mm
Sand
0.05-2 mm
Silt
0.002-0.05
mm
Clay
less than
0.002 mm
Soil Properties
3. pH
− Influences uptake
of nutrients by
plants
© Cengage Learning 2015
4. Fertility
− 20 minerals
needed for plant
growth
− Major nutrients =
nitrogen,
phosphorus &
potassium
Topsoil Erosion Is a Serious Problem in
Parts of the World
• Soil erosion
– Movement of soil by
wind and water
– Natural causes
– Human causes
• Two major harmful effects
of soil erosion
– Loss of soil fertility
– Water pollution
© Cengage Learning 2015
Drought and Human Activities Are
Degrading Drylands
• Desertification
– Productive potential of topsoil falls by 10% or more
– Prolonged drought, human activities
• Human agriculture accelerates desertification
• Dust bowl
– Severe wind erosion of topsoil
– Combination of poor cultivation practices & prolonged
drought
© Cengage Learning 2015
Excessive Irrigation Has Serious
Consequences
• Soil salinization
– Gradual accumulation of salts in the soil from
irrigation water
– Lowers crop yields and can even kill plants
– Affects 10% of world croplands
• Waterlogging
– Saturation of soil with
irrigation water or excess
precipitation
– Water table rises close to the
© Cengage Learning 2015
surface
Many Farmers Are Reducing Soil Erosion
• Soil conservation
– Terracing
– Contour planting
– Strip cropping with cover crop
– Alley cropping, agroforestry
– Windbreaks or shelterbelts
– Conservation-tillage farming
• Identify erosion hotspots
© Cengage Learning 2015
We Can Restore Soil Fertility
• Organic fertilizer
– Animal manure
– Green manure
– Compost
• Manufactured inorganic
fertilizer
– Nitrogen, phosphorus,
and calcium
• Crop rotation
© Cengage Learning 2015
US Legislation
• Soil Conservation Act of 1935: law
organized the Soil Conservation Service
which is now called the Natural Resources
Council
• Food Security Act or Farm Bill of 1985:
Law required US farmers to control
erosion on land that was subject to large
amounts of soil loss
– If they failed to do so, lost government price
© Cengage Learning 2015 supports for product