Download Bio 126 Introduction to Geology

Bio 126
Introduction to
Geology
Overview
•
•
•
•
What is Geology
the Earth’s structure
Geologic changes
Internal process
– Plate tectonics
– Rock cycle
• Rock types
• External process
– Erosion
– Weathering
– Soil formation
• Geology is the study of the Earth,
primarily by studying rocks
• Rocks are aggregates of minerals
• Minerals are naturally formed, solid,
inorganic substances having specific
chemical compositions and crystal
structure
Earth’s Layers- Core
• At the center of the earth is the core
that is divided into two parts:
– Inner –Solid ball of iron and nickel
about 1,490 miles thick
– Outer – Molten of iron and nickel, about
1,430 miles thick
Earth’s Layers- Outside Core
are the Mantle layers:
• Solid Mantle layer –lower mantle mostly
solid about 1,740 miles thick
• Outer Mantle divided into two layers
– Asthenosphere - Outer molten layer of mantle
is “plastic consistency” silicate materialcontinents float on this layer
– Lithosphere- Rock layers that form surface of
the earth – we walk on this layer
• Outer-most solid layer of mantle material.
• Crust material
Earth’s Layers - Crust
• Outermost solid very thin layer, floating
on molten Asthenosphere mantle
material
• Oceanic Crust is thinner, only 3 miles
thick
• Continental Crust is thicker up to 12-40
miles thick
• Cracks into Tectonic plates which bump
into each other. These land movements
we call Plate Tectonics, and cause
earthquakes.
Oceanic
Crust
Atmosphere
Vegetation
Biosphere
and animals
Soil
Crust
Rock
Continental
Crust
Lithosphere
Upper mantle
Asthenosphere
Lower mantle
Core
Mantle
Crust (soil
and rock)
Biosphere
Hydrosphere (living and dead
(water)
organisms)
Lithosphere
Atmosphere
(crust, top of upper mantle)
(air)
Fig. 3-6, p. 54
Layers of the Earth
35 km (21 mi.) avg., 1,200˚C
Crust
100 km (60 mi.)
200 km (120 mi.)
Crust
Low-velocity zone
Mantle
Lithosphere
Solid
10 to 65km
2,900km
100 km
(1,800 mi.)
3,700˚C
Outer core
(liquid)
Core
Asthenosphere
(depth unknown)
200 km
5,200 km (3,100 mi.), 4,300˚C
Inner
core
(solid)
Fig. 10.2, p. 212
Volcanoes
Abyssal hills
Oceanic crust
(lithosphere)
Abyssal Oceanic
floor
ridge
Abyssal
floor
Trench
Folded
mountain
belt
Abyssal plain
Craton
Continental
shelf
Continental
slope
Continental
rise
Continental crust (lithosphere)
Mantle (lithosphere)
Fig. 15-2, p. 336
Plate tectonics
• The study of the deformation and
movement of earth structures in semi
rigid lithosphere.
• Internal forces from the core create heat
that keeps asthenosphere molten. It
slowly flows.
– Convection cells – Heated magma flows up,
and cool near surface and moves back
down.
– Mantle Plumes bring hot magma towards
surface like a fountain
Convection Cell in Mantle
Spreading
center
Collision between
two continents
Subduction
zone
Continental
crust
Oceanic
crust
Ocean
trench
Oceanic
crust
Continental
crust
Material cools Cold dense
as it reaches material falls
the outer back through
mantle
mantle
Hot
Mantle
material
convection
rising
cell
through
the
mantle
Two plates move
towards each other.
One is subducted
back into the mantle
on a falling convection
current.
Mantle
Hot outer
core Inner
core
Fig. 15-3, p. 337
Plate
tectonicsDivergent
Areas
Lithosphere
Asthenosphere
Oceanic ridge at a divergent plate boundary
• Plates spread apart in Divergent (constructive)
areas forming new land as mantle material
flows upwards.
– Makes thinner Basalt Plate
– Oceanic ridges still growing, as in Atlantic
Ocean.
– Rift valleys form on divergent land areas
Fig. 10.6a
Slide
Convergent zones
•
•
•
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Plates move together and collide
An Oceanic Plate sinks under Continental in a Subduction
zone.
– Along California, the Pacific Plate collides with and is
is moving underneath North American Plate.
– The Subducted Plate melts into asthenosphere
convection cell, as it does molten rock moves up into
crust of other plate. Lands uplifted, mountains
(Sierras) form.
Causes Earthquakes, volcanoes
Continental plates collide neither subducts, both deform,
mountains rise- Himalayas.
Arc Island Chains
• Some of the subducted plate material is
scrapped onto the Continental plate.
• Form while still off shore of continental
plate
• Forms Arc Islands
• Japan
• Arc Islands formed part of what became
the North Coast ranges
Trench
Volcanic island arc
Convergent plates
Rising
magma
Subduction
zone
Lithosphere
Asthenosphere
Trench and volcanic island arc at a convergent
plate boundary
Fig. 10.6b, p. 215
Slide 8
Fracture zone
Transform
Faults
Transform
fault
Lithosphere
Asthenosphere
Transform fault connecting two divergent plate boundaries
• Plates in opposite directions in a fault
• Run parallel to each, not colliding
• Stresses as plates slip by each other
cause earthquakes
• Example: San Andreas Fault
Fig. 10.6c, p. 215
Slide 9
Plate Tectonic Movements
Plate Map
Reykjanes
Ridge
EURASIAN PLATE
JUAN DE
FUCA PLATE
CHINA
SUBPLATE
Transform
fault
PHILIPINE
PLATE
PACIFIC
PLATE
MidIndian
Ocean
Ridge
Transform
fault
INDIAN-AUSTRLIAN PLATE
Southeast Indian
Ocean Ridge
NORTH
AMERICAN
PLATE
COCOS
PLATE
East Pacific
Rise
MidAtlantic
Ocean
Ridge
EURASIAN
PLATE
ANATOLIAN
PLATE
CARIBBEAN
PLATE
ARABIAN
PLATE
AFRICAN
PLATE
SOUTH
AMERICAN
PLATE
Carlsberg
Ridge
AFRICAN
PLATE
Transform
fault
Southwest Indian
Ocean Ridge
ANTARCTIC PLATE
Convergent
plate boundaries
Plate motion
at convergent
plate boundaries
Divergent ( ) and
transform fault (
boundaries
)
Plate motion
at divergent
plate boundaries
Fig. 10.5b, p. 214
Slide 6
Earthquakes
Liquefaction of
recent sediments
causes buildings
of sink
Two adjoining plates
move laterally along
the fault line
Earth movements
Cause flooding in
Low-lying areas
Landslides may
occur on
hilly ground
Shock
waves
Epicenter
Focus
Fig. 10.9, p. 217
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•
•
Slide 12
Abrupt movement along a fault line
Energy move out in shock waves
Focus is the point of initial movement
Epicenter is location on surface above
focus.
Earthquake Faults
• Strike – Slip faults move sideways
– San Andreas
• Dip-Slip faults move up / down motion
– Uplifting mountains
– Grabens form when an area drops down
• Livermore Valley, Lake Tahoe
“Richter Scale”
Moment magnitude scale
•
•
Magnitude of
earthquake Measured
on a seismograph
Each unit has ten
times greater the
impact
– 5.0 is 10x greater
then a 4.0.
Less than
4.0
4.0-4.9
insignificant
5.0-5.9
damaging
6.0-6.9
destructive
7.0-7.9
major
Over 8.0
great
minor
The Ring Of Fire
Volcanoes
Earthquakes
Fig. 10.5a, p. 214
Slide 5
Plate Map
Reykjanes
Ridge
EURASIAN PLATE
JUAN DE
FUCA PLATE
CHINA
SUBPLATE
Transform
fault
PHILIPINE
PLATE
PACIFIC
PLATE
MidIndian
Ocean
Ridge
Transform
fault
INDIAN-AUSTRLIAN PLATE
Southeast Indian
Ocean Ridge
NORTH
AMERICAN
PLATE
COCOS
PLATE
East Pacific
Rise
MidAtlantic
Ocean
Ridge
EURASIAN
PLATE
ANATOLIAN
PLATE
CARIBBEAN
PLATE
ARABIAN
PLATE
AFRICAN
PLATE
SOUTH
AMERICAN
PLATE
Carlsberg
Ridge
AFRICAN
PLATE
Transform
fault
Southwest Indian
Ocean Ridge
ANTARCTIC PLATE
Convergent
plate boundaries
Plate motion
at convergent
plate boundaries
Divergent ( ) and
transform fault (
boundaries
)
Plate motion
at divergent
plate boundaries
Fig. 10.5b, p. 214
Slide 6
Plate tectonics
• Over time great movements of the continents
have taken place.
• Pangea formed when all the continents
collide into one large land mass, about 250
Million years Ago
• It then broke into Laurasia and
Gondwanaland – 135 MYA
– In recent Geologic time, Europe and North
America Touched for a long time and we share
many species
• Current configuration only about 10 MYA
– South and North America join recently with CA
– Land bridge. Species still migrating across.
History of
Continental
Drift
Mountain Building
Three Rock Types:
• Igneous –unchanged cooled mantle
material (Magma)
• Sedimentary – weathered products of
other rocks compacted together
• Metamorphic – reworked rocks.
Stressed by heat and pressure.
Igneous Rocks
Abyssal
hills
Abyssal Oceanic
floor
ridge
Oceanic crust
(lithosphere)
• Plutonic or Intrusive
Rocks form by cooling
magma under earth’s surface.
Abyssal
floor
Abyssal plain
Pluton
Mantle (lithosphere)
Trench
Folded mountain belt
Craton
Volcanoes
Continental
shelf
Continental
slope
Continental crust
(lithosphere)
Mantle
(lithosphere)
Mantle (asthenosphere)
– Ex. Granite
– May be brought up in very large blocks called
Batholiths such as the Sierra Nevada. These
form as Plutons of new molten rock merge lower
down in crust.
• Volcanic or Extrusive Rocks cool rapidly at
the earth’s surface.
– Ex. Pumice, Lava Stone
A
Rock Crystals
• Form as magma cools
• Large crystals
– form over a longer period of time – a slower
cooling period
– Form deeper down on crust - intrusive
– Coarse grain rock with visible crystals granite
• Volcanic activity has fastest cooling on
surface - extrusive
– Forms very fine grain crystals
Sierra
Granite
Large Crystal sizes
Sedimentary Rocks
• Only 5% of crust, but make up 75% of
rocks found on surface.
• Laid down in layers or beds called
Strata under water, then compacted.
• Three types by origin of rock material:
– Clastic (particles)– weathering of other
rocks and deposition of debris
– Chemical – precipitations in sea
– Organic “Rock”
Classification of sediments
based on particle size
Sediment
Gravel
Very Coarse Sand
Coarse Sand
Medium Sand
Fine Sand
Very Fine Sand
Silt
Clay
Particle Size (mm)
Larger than 2.0
2.0 – 1.0
1.0 – 0.5
0.5 – 0.25
0.25 – 0.10
0.10 – 0.05
0.05 – 0.002
Less than 0.002
Parent material
(rock)
Biological
weathering
(tree roots and
lichens)
Chemical
weathering
(water, acids,
and gases)
Particles of parent material
Physical weathering
(wind, rain, thermal
expansion and
contraction, water
freezing)
Fig. 15-6, p. 340
Sand
0.05–2 mm
diameter
Silt
0.002–0.05 mm
diameter
Water
High permeability
Clay
less than 0.002 mm
diameter
Water
Low permeability
Fig. 3-25, p. 70
Clastic Sedimentary Rocks
• Named by clastic (particle) size that
makes up the framework of the rock
• Smallest to largest particles:
– Shale - Forms in Clay deposits
– Siltstone – Forms in Still water
– Sandstone – Forms in Slow moving water,
marine seas, bays
– Conglomerate – Gravel, pebbles & larger forms
in high energy environments.
– Breccia – angular rocks in conglomerate.
• Smaller particles (clay & silt) travel
farther, settle in low energy areas.
Chemical Sedimentary Rocks
• From from the precipitation of dissolved
substances as water evaporates
– Limestone – calcium carbonate in water
• May also be biological (organic)
– Halite – Salt dissolved in water and
deposited as water evaporates.
• Has be mined for years in areas. Leaves salt caves
– Chert – Silica Dioxide:Flint, Jasper, Petrified
Wood
– Gypsum – Calcium Sulfate – Plaster,
Alabaster
Organic or Biological Sedimentary
“Rocks”
• Deposits of organic material, fossils
• Not a true rock, not true minerals
• Limestone- also may form as deposits of
marine fossil skeletons & shells.
– Most of organic material decomposed, oncemineralized part remains (Microscopic
shells).
• Coal – only partially decomposed,
deposits of organic material – still energy
rich.
Metamorphic Rocks
• Altered rocks
• Formed by intense heat and pressure
of being buried
• Recrystallize to form new minerals
• Often form layers perpendicular to
direction of pressure – clue to
mountain building events.
Partial List of Metamorphic
Rocks (* know these)
Metamorphic Rock
Original Rock
Slate
Shale
Quartzite
Quartz Sandstone
Schist
Slate
Gneiss
Granite
Marble
Limestone
Serpentine
Basalt, Grabbro
Tectonic – Rock Cycle
• New Rocks form from mantle material
– Either as old plates melt into lower lithosphere
and plutons of new rock rise up
– Or as lava emerges from a volcano / vent
• Sedimentary Rocks form from weathering &
deposition
• Metamorphic Rocks form as tectonic
movements that only partially melt rocks
The Rock Cycle
Transportation
Deposition
Sedimentary Rock
Slate, sandstone,
limestone
Erosion
Heat,
pressure,
stress
Weathering
EXTERNAL PROCESSES
INTERNAL PROCESSES
Igneous Rock
Granite, pumice,
basalt
Cooling
Heat, pressure
Magma
(molten rock)
Metamorphic Rock
Slate, marble,
quartzite
Melting
Fig. 10.8, p. 217
Erosion
Transportation
Weathering
Deposition
Igneous rock
Granite,
pumice,
basalt
Sedimentary
rock
Sandstone,
limestone
Heat, pressure
Cooling
Heat, pressure,
stress
Magma
(molten rock)
Melting
Metamorphic rock
Slate, marble,
gneiss, quartzite
Fig. 15-8, p. 343
Geologic changes
• Internal processes
– Heat from interior
– Gravity
• External processes
– Erosion
– Weathering
• Chemical
• Physical
Soil forms from external
processes
• Erosion
– Material is dissolved or worn away and
moved by wind, water,etc.
– Streams, rivers most important agents
• Weathering loosens material from rocks
– Mechanical – frost wedging. Water moves
into crack, freezes and expands breaking
off chips.
– Chemical- water and acids, bases break
down rock, very important in soil formation.
It continues even under ground.
External Processes and the
Landscape
Lake
Tidal
flat
Glacier
Spits
Stream
Lagoon
Dunes
Shallow marine
environment
Barrier
islands
Delta
Dunes
Beach
Shallow marine
environment
Volcanic
island
Coral reef
Continental shelf
Continental slope
Continental rise
Abyssal plain
Deep-sea fan
Fig. 10.7, p. 216
Slide 10
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•
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•
•
•
•
Valleys
Plains
Marshes
Deltas
Lakes
Dunes
Beaches
Bays
Soil
Composed of three components:
• Eroded Parent Rock (dirt)
– May determine special soils like serpentine
– Broken down by weathering – the physical
and chemical processes.
• Organic Matter builds up as the remains
of plants and animals living on the soil
• Soil has an entire unique Living
Microflora of bacteria, algae, fungi, and
micro animals
Soil Profile - Formation
Oak tree
Fern
Word
sorrel
Lords and
ladies
Dog violet
Earthworm
Millipede
Mole
Honey
fungus
Grasses and
small shrubs
Organic debris
Builds up
Moss and
lichen
Rock
fragments
O horizon
Leaf litter
A horizon
Topsoil
Bedrock
B horizon
Subsoil
Immature soil
Regolith
Young soil
Pseudoscorpion
C horizon
Parent
material
Mite
Nematode
Actinomycetes
Root system
Mature soil
Red earth
mite
Springtail
Fungus
Bacteria
Fig. 10.12, p. 220
Soil Layers – or Horizons
• O horizon – surface layer
– Freshly fallen plant debris,animal wastes
• A horizon – humus layer
– Partially decomposed organic matter
– Some inorganic minerals
– Darker and looser (porous) than deeper
layers
• O & A layers essential for plant growth
– Anchored by plant roots, trap nutrients
– ALIVE !! Teams with micro flora, bacteria,
fungi
• C Horizon – parent Rock material
Simplified Soil Food Chain
Rove beetle
Pseudoscorpion
Flatworm
Centipede
Ant
Ground
beetle
Mite
Adult
fly
Roundworms
Fly
larvae
Beetle
Protozoa
Mites
Springtail
Millipede
Bacteria
Sowbug
Slug
Fungi
Actinomycetes
Snail
Mite
Earthworms
Organic debris
Fig. 10.13, p. 221
Slide 16
Soil Conservation
• Loss of O & A layers can doom agriculture
• Tilling of soil increase erosion
• Poor agricultural practice and drought made
the Dust Bowl of 1930’s.
• Soil Erosion Act passed congress in 1935
Kansas
Colorado
Dust
Bowl
Oklahoma
New Mexico
Texas
MEXICO
Fig. 10.20, p. 227
Slide 24
Areas of Soil Erosion
Areas of serious concern
Areas of some concern
Stable or nonvegetative areas
Fig. 10.19, p. 226
Desertification
•
•
•
•
•
•
Loss of agriculture ability in dry areas.
lose of top soil due to overgrazing
Deforestation
Tilling steep hillsides
Soil compaction by machinery
Salinization – irrigation water evaporates
leaving a buildup of salts in soil
– 35% of California crop lands suffer from levels of
salinization
Fig. 10.23, p. 229
Severe salinization in Colorado
Slide 27
Desertification
Moderate
Severe
Very Severe
Fig. 10.21, p. 228
Stopping Soil Erosion
• Terracing- making flat plateaus in hillsides
– Good on steep slopes
– Traditional form for rice in Bali, Andes etc.
• Contour cropping –plowing rows with across
slope.
– Good on gentle slopes
• Strip cropping alternate rows of crops
– corn & alfalfa
– One traps soil eroded by the food crop.
• Agroforestry – several crops are planted
together in rows between trees
– Trees block wind, provide fruit, mulch, fuel
• Terracing,
contour planting,
strip cropping,
alley cropping,
and windbreaks
can reduce soil
erosion.
Figure 13-16