GeologyGeology

Earth’s StructureEarth’s Structure

Name the zones of the earthCrust, mantle, core

Now do it again with more detailCrust, lithosphere, asthenosphere, mantle, outer core, inner core

Fig. 10.2, p. 212

Mantle

Core

Crust

Low-velocity zone

Solid

Outer core(liquid)

Innercore(solid)

35 km (21 mi.) avg., 1,200˚C

2,900km(1,800 mi.)3,700˚C

5,200 km (3,100 mi.), 4,300˚C

10 to 65km

100 km

200 km

100 km (60 mi.)200 km (120 mi.)

Crust

Lithosphere

Asthenosphere(depth unknown)

What is in each zoneWhat is in each zone

Core – mostly iron and a little nickel, inner solid and outer is liquid

Mantle – mostly iron, silicon, oxygen, and magnesium, mostly rigid except near surface which is plastic (asthenosphere)

Crust – mostly oxygen, silicon, aluminum, and iron (by weight)

Convection belowConvection below

Heat from the formation of the earth combined with energy from radioactive decay gives way to convection currents of rock (very slow) or mantle plumes in which hot rock rises

Plate tectonicsPlate tectonics

The lithosphere is broken into many large plates which move due to convection currents within the asthenosphere

Remember continental drift (Pangaea)

Fig. 10.5b, p. 214

EURASIAN PLATE

CHINASUBPLATE PHILIPINE

PLATE

INDIAN-AUSTRLIAN PLATE

PACIFICPLATE

JUAN DEFUCA PLATE

COCOSPLATE

CARIBBEAN PLATE

NORTHAMERICAN

PLATE

SOUTHAMERICAN

PLATE

EURASIAN PLATE

ANATOLIAN PLATE

ARABIAN PLATE

AFRICAN PLATE

AFRICAN PLATE

CarlsbergRidge

Southwest IndianOcean Ridge

ANTARCTIC PLATE

Transformfault

East PacificRise

Transformfault

Mid-IndianOceanRidge

Southeast IndianOcean Ridge

Mid-AtlanticOceanRidge

ReykjanesRidge

Transformfault

Divergent ( ) andtransform fault ( )boundaries

Convergentplate boundaries

Plate motionat convergentplate boundaries

Plate motionat divergentplate boundaries

Plate boundariesPlate boundaries Divergent – plates move apart, form mid ocean ridges

Convergent – plates slam together, form largest mountains in the world

Subduction is a type of convergent where one plate dives beneath another and usually creates trenches and volcanoes nearby

Transverse – slide sideways past each other (San Andreas Fault)

Fig. 10.6b, p. 215

Lithosphere

Trench Volcanic island arc

Asthenosphere

Risingmagma

Subductionzone

Trench and volcanic island arc at a convergentplate boundary

Fig. 10.6c, p. 215

Fracture zone

Transformfault

Lithosphere

Asthenosphere

Transform fault connecting two divergent plate boundaries

Fig. 10.6a, p. 215

Lithosphere

Asthenosphere

Oceanic ridge at a divergent plate boundary

Fig. 10.3, p. 213

Oceanic crust(lithosphere)

Abyssalhills Abyssal

floorOceanic

ridgeTrench

Volcanoes

Folded mountain belt

Craton

Mantle (lithosphere)

Mantle (asthenosphere)

Ab

ys

sa

l p

lain

Continental crust(lithosphere)

Mantle(lithosphere)

Continentalrise

Continentalslope

Continentalshelf

Abyssal plain

Abyssalfloor

Erosion and WeatheringErosion and Weathering These are the external processes Erosion is the moving of rock material from one

place to another (deposition)

Weathering is the breaking down of rock by natural forces

Ice wedging, rain, wind, gravityChemical weathering, carbonic acid

Fig. 10.7, p. 216

Dunes Lagoon

SpitsStream

Glacier

Lake

Tidalflat

Barrierislands

Shallow marineenvironment

Volcanicisland

Coral reef

Abyssal plain

Deep-sea fan

Continental shelf

Continental slope

Continental rise

DeltaDunes

Beach

Shallow marineenvironment

Rocks and mineralsRocks and minerals

Mineral – an element or inorganic compound that occurs naturally, is solid, and has a regular crystalline internal structure

Rock – type of music meant to be played loud, also any material that makes up a large, natural, continuous part of the earth’s crust

Types of rockTypes of rock

IgneousGranite, pumice, basalt

SedimentaryShale, sandstone, limestone (coral reef)

MetamorphicSlate, marble, quartzite

Fig. 10.8, p. 217

Igneous RockGranite, pumice,

basalt

Metamorphic RockSlate, marble,

quartzite

Magma(molten rock)

Cooling

Heat, pressure

Melting

Heat,pressure,

stress

Sedimentary RockSlate, sandstone,

limestoneDepositionTransportation

Erosion

Weathering

EXTERNAL PROCESSES

INTERNAL PROCESSES

EarthquakeEarthquake Fault – break in the lithosphere Focus – where the earthquake took place Epicenter – location above focus at surface Richter scale – used to measure magnitude, less than 3

is not felt, logarithmic scale, so each increase of 1 is a factor of 10

Minor < 5, damaging 5-6, destructive 6-7, major 7-8, great over 8

Aftershock – reduced shaking after original movement

Volcano – it can happen here!Volcano – it can happen here! Volcano - Wherever magma reaches the surface

through a vent or fissure (also released are gases carbon dioxide, water vapor, hydrogen sulfide, ash, and other ejecta

Mt. St. Helens – worst US volcano disaster

Ring of fire – other than a song by Social D, this is the edge of the pacific plate where most volcanoes are located

SoilSoil

Produced slowly (200-1000 years typically) by weathering of rock, deposition of sediments, and decomposition of organic matter

Soil horizons – separate zones within soil Soil profile – cross-section view of soil

HorizonsHorizons O horizon – surface litter A horizon – top soil, made up of inorganic

particles (clay, silt, sand) and humus (organic particles from decomposed organisms)

Dark topsoil is richer in nutrientsReleases water and nutrients slowlyProvides aeration to rootsHealthy soil contains many nematodes and bacteria, fungi, etc.

Fig. 10.12, p. 220

Oak tree

Fern

O horizonLeaf litter

A horizonTopsoil

B horizonSubsoil

C horizonParent

material

Root system

Mature soil

Red earthmite Springtail

Bacteria

Fungus

Actinomycetes

Nematode

Mite

Pseudoscorpion

Young soil

Regolith

Bedrock

Immature soil

RockfragmentsMoss and

lichen

Organic debrisBuilds upGrasses and

small shrubsMole

Dog violet

Honeyfungus

Millipede

Earthworm

Lords andladiesWord

sorrel

Poor topsoilPoor topsoil Grey, yellow and red are not the colors of healthy

topsoil Generally means that soil is lacking nutrients

Best soil is called loam with equal parts sand, silt, clay and humus

Leaching – dissolving and carrying nutrients (or pollutants) through soil into lower layers

B – horizon and C - horizonB – horizon and C - horizon

B – Subsoil mostly broken down rock with little organic matter

C- parent material broken down rock on top of the bedrock

SoilsSoils

Texture – relative amount of different sized particles present (sand, silt, clay)

Porosity – volume of pore space in the soil Permeability – the ability of water to flow through

the soil

Water Water

High permeability Low permeability

Sandy soil Clay soil

SoilsSoils

Clay – high porosity, low permeability Sand – high permeability, low porosity

Acidity is another factor Where rain is low, calcium and other alkaline

compounds may build up (sulfur can be added – turns to sulfuric acid by bacteria)

Fig. 10.15b, p. 223

Acidiclight-coloredhumus

Iron andaluminumcompoundsmixed withclay

Forest litterleaf mold

Humus-mineralmixture

Light, grayish-brown, silt loam

Dark brownFirm clay

Acid litterand humus

Humus andiron andaluminumcompounds

Light-coloredand acidic

Tropical Rain Forest Soil(humid, tropical climate)

Deciduous Forest Soil(humid, mild climate)

Coniferous Forest Soil(humid, cold climate)

Fig. 10.15a, p. 223

Weak humus-mineral mixture

Mosaicof closelypackedpebbles,boulders

Dry, brown toreddish-brownwith variableaccumulationsof clay, calciumcarbonate, andsoluble salts

Desert Soil(hot, dry climate)

Grassland Soil(semiarid climate)

Alkaline,dark,and richin humus

Clay,calciumcompounds

Soil erosionSoil erosion

Causes – mainly water and wind Human induced causes – farming, logging,

mining, construction, overgrazing by livestock, off-road vehicles, burning, and more (go us!)

Soil erosionSoil erosion Types Sheet

Uniform loss of soil, usually when water crosses a flat field

RillFast flowing water cuts small rivulets in soil

GullyRivulets join to become larger, channel becomes wider and deeper, usually on steeper slopes or where water moves fast

Global soil lossGlobal soil loss This is a major problem world wide Have lost about 15% of land for agriculture to soil

erosionOvergrazingDeforestationUnsustainable farming

Also 40% of ag land is seriously degraded due to soil erosion, salinization, water logging and compaction

Fig. 10.21, p. 228

Moderate Severe Very Severe

Desertification of arid and semiarid lands

Fig. 10.19, p. 226

Areas of serious concern

Areas of some concern

Stable or nonvegetative areas

Global soil erosion

DesertificationDesertification Turning productive (fertile) soil into less

productive soil (10% loss or more)OvergrazingDeforestationSurface miningPoor irrigation techniquesPoor farming techniquesSoil compaction

SalinizationSalinization As water flows over the land, salts are leached out When water irrigates a field it is left to evaporate

typically This repeated process causes the dissolved salts to

accumulate and possibly severely reduce plant productivity

Fields must be repeatedly flushed with fresh water to remove salt build up

WaterloggingWaterlogging When fields are irrigated they allow water to sink

into the soil. Winds can dry the surface As more water is applied the root area of plants

is over saturated reducing yield

As clay is brought to subsoil levels it can act as a boundary for water infiltration

Fig. 10.22, p. 229

Evaporation

Evaporation TranspirationEvaporation

Waterlogging

Less permeableclay layer

Soil conservationSoil conservation

Conservation tillage – (no till farming) disturb the soil as little as possible

Reducing erosion also helps – save fuel, cut costs, hold water, avoid compaction, allow more crops to be grown, increase yields, reduce release of carbon dioxide

Soil conservationSoil conservation Terracing – making flat growing areas on

hillsides Contour farming – planting crops perpendicular

to the hill slope, not parallel Strip cropping – planting alternating rows of

crops to replace lost soil nutrients (legumes) Alley cropping – planting crops between rows of

trees

Fig. 10.24b, p. 230

Control planting and strip cropping

Fig. 10.24c, p. 230

Alley cropping

Fig. 10.24a, p. 230

Terracing

Soil conservationSoil conservation Gully reclamation – seeding with fast growing native

grasses, slows erosion or “reverses” itAlso building small dams traps sedimentsBuilding channels to divert water or slow water

Windbreaks – trees planted around open land to prevent erosion

Retains soil moisture (shade, less wind)Habitats for birds, bees, etc.

Land classification – identify marginal land that should not be farmed

Fig. 10.24d, p. 230

Windbreaks

Soil fertilitySoil fertility

Inorganic fertilizers – easily transported, stored, and applied

Do not add humus – less water and air holding ability, leads to compactionOnly supply about 3 of 20 needed nutrientsRequires large amount of energy for productionReleases nitrous oxide (N2O) during production, a green house gas

Soil fertilitySoil fertility Organic fertilizers – the odor is a problem Animal manure – difficult to collect and transfer

easily, hard to store Green manure – compost, aerates soil, improves

water retention, recycles nutrients Crop rotation – allows nutrients to return to soil,

otherwise same crop continually strips same nutrient, keeps yields high, reduces erosion

See you on the farm!See you on the farm! Remember without

farming we all starve

But unless we change our farming practice we continue to damage our environment