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9. Our Living Earth
•  Earth’s
atmosphere, oceans & surface
•  Earth’s
interior & earthquakes
•  Earth’s
plate tectonics activity
The Earth: A Portrait From Space
•  Earth’s magnetic field & magnetosphere
•  Earth’s
evolving atmosphere
•  Earth’s
human population & biosphere
Earth Data (Table 9-1)
Earth From An Apollo Spacecraft
Earth’s Environmental Spheres
Rocks
•  Earth’s
spheres
–  Geosphere
–  Hydrosphere
–  Atmosphere
–  Biosphere
•  Definition
Rock & metallic Earth materials
Water as ice, liquid & humidity
~78% nitrogen & ~21% oxygen
All living things (biomass)
•  Earth’s ecosystem
–  Matter flows
•  A closed system for most practical purposes
–  Meteoroids enter daily, spacecraft leave occasionally
–  Energy flows
•  An open system for most practical purposes
–  Sunlight brings extremely large amounts of energy on one side
–  Radiant heat in extremely large amounts leaves
on all sides
–  Consolidated mixture of one or more minerals
•  Monomineralic rocks have many crystals of 1 mineral
•  Polymineralic rocks have many crystals of >2 minerals
•  Making rocks
–  Igneous
processes Fiery origins
–  Sedimentary processes Cemented small particles
–  Metamorphic processes Changed by heat/pressure
•  Destroying rocks
–  Physical / mechanical weathering
–  Chemical weathering
Rock Cycle: Materials & Processes
Rock Cycle
•  Materials
–  Magma
solidifies
& becomes…
–  Igneous
rock
weathers
& becomes…
–  Sediment
lithifies
& becomes…
–  Sedimentary rock metamorphoses & becomes…
–  Metamorphic rock
melts
& becomes…
•  Processes
–  Solidification
–  Weathering
–  Lithification
–  Metamorphism
–  Melting
produces
igneous
rock
produces
sediment
produces sedimentary rock
produces metamorphic rock
produces
magma
Magma: Source of Igneous Rocks
Some Common Igneous Rocks
•  Earth’s interior is hot
–  Residual heat of formation ~ 4.6 billion years ago
–  Decay of radioactive isotopes
•  Earth’s interior is mostly solid or “plastic”
–  Solid: Rigid / brittle under intense pressure
–  Plastic: Flows slowly under intense pressure
•  Localized areas are hot enough to melt rocks
–  Magma temperatures vary ~ 600°C to ~ 1,400°C
–  Iron turns red at ~ 600°C & melts at ~ 1,500°C
•  Magma has ~ 10% greater volume than source
–  Same mass ⇒ Greater volume ⇒ Lower density
Sedimentary Rock Categories
•  Organic
–  Coal
•  Clastic
Remains of plants & animals
Fossilized fern leaves
Broken rock & mineral fragments
–  Sandstone, shale & limestone
•  Bioclastic
–  Coquina
•  Chemical
–  Gypsum
Broken shell fragments
Limestone “fossil hash”
Crystallization from water solution
A common “evaporite” mineral
Some Clastic Sedimentary Rocks
Three Metamorphic Processes
•  Heat
Foliated Metamorphic Rocks: Gneiss
Absolutely essential
–  Hot enough for atoms & molecules to slowly migrate
–  Cool enough so that nothing melts
•  Pressure
Common but not essential
–  Subduction zones
Pacific Northwest
–  Regional subsidence
Mississippi Delta
•  Fluids
Only near active volcanoes
–  Volcanically active areas Eastern Oregon
Oregon’s Metamorphic Environment
Earth’s “Chemical” Differentiation
Portland
Astoria
Characterizing Earth’s Interior
•  Chemical composition
–  Low
Mineral composition
density minerals
•  Granite continents & basalt ocean basins
–  Intermediate density minerals
•  Peridotite
–  High
•  Iron & nickel
density minerals
•  Physical condition
Crust
Mantle
Core
Solid / plastic / liquid
–  A function of temperature & pressure
•  Temperature increases slowly with depth
•  Pressure
increases rapidly with depth
–  Solid
–  Plastic
–  Solid
–  Liquid
–  Solid
Lithosphere
Asthenosphere
Mantle
Outer core
Inner core
Old & cool enough
Lubricating layer
Very slightly plastic
Temperature wins
Pressure wins
Earth’s Interior Facts & Evidence
•  Some
basic
facts
–  Overall average density ~ 5.5
g . cm–3
–  Surface average density ~ 2.7 to 3.0 g . cm–3
–  Interior must have higher density materials
•  Much higher atomic number ⇒ Metals
•  Greater compression due to greater pressure
•  Some suggestive evidence
–  Asteroids orbiting the Sun
•  Range of materials from rock to iron/nickel
•  Proportions would produce a planet like Earth
–  Meteorites found on Earth
•  Range of materials from rock to iron/nickel
•  Proportions would produce a planet like Earth
Earth’s Layers: The Lithosphere
Earth’s Layers: Crust/Mantle/Core
Earthquake Focus & Epicenter
Seismic (Earthquake) Waves
•  Body waves
–  Source location: Focus
•  Place of maximum underground shaking
•  Place where the earthquake begins
Usually ! ! !
–  Varieties
•  Compressional waves
•  Transverse
waves
P-waves
S-waves
Primary waves
Secondary waves
•  Surface waves
–  Source location: Epicenter
•  Place of maximum surface shaking
•  Place directly above the focus
The focus is also called the hypocenter
–  Varieties
•  Compressional waves
•  Transverse
waves
Compressional & Transverse Waves
Compressional Seismic Waves
Transverse Seismic Waves
Usually ! ! !
Sideways jolting
Up & down jiggling
Body Seismic Waves
Surface Seismic Waves
Seismicity & Earth’s Internal Structure
Plate Tectonics
Mantle Convection & Plate Motion
•  Tectonic plates = Lithospheric plates
•  Thermal gradient: Hotter at core than at crust
–  Results in a density gradient
–  Rigid & brittle
•  Heat sources
•  “Glide” over the asthenosphere
–  Sizes vary greatly
–  Planetesimal impact
Dominant as a protoplanet
Ongoing exponential decay
•  Micro plates
Juan de Fuca plate
–  Radioactive decay
•  Macro plates
Pacific
–  Gravitational collapse
plate
•  Three kinds of tectonic plates
–  Oceanic
plates
Basaltic composition
–  Continental plates
Granitic composition
–  Composite
Both basalt & granite
plates
A Model of Mantle Convection
Minimal as a protoplanet
•  Point of origin
–  Thought to be the core-mantle boundary
•  Shape
–  Elongated “curtains” of rising material
A Global View of Mantle Convection
Tectonic Plates
Tectonic Plate Boundary Processes
Divergent Plate Boundaries
Convergent Plate Boundaries
Transform Plate Boundaries
Mid-Atlantic Ridge Spreading Zone
Ridge offset by transform
faults
Effects of Plate Motion: Volcanoes
•  Divergent tectonic plate boundaries
–  Most rising magma spreads out under lithosphere
•  Lithosphere warms ⇒ Lowers density ⇒ Floats higher
•  Penetrates the lithosphere, causing eruptions
•  Convergent tectonic plate boundaries
–  Highest density plate subducts
•  Ocean ⇒⇐ ocean collision
–  Oldest (i.e., coldest & densest) basaltic plate subducts
–  Basaltic to andesitic lavas build gently curving line of volcanoes
•  Ocean ⇒⇐ continent collision
–  Basaltic (therefore most dense) oceanic plate subducts
–  Andesitic to rhyolitic lavas build gently curving line of volcanoes
Plate Motion Effects: Mountains
•  Volcanoes
–  Usually occur at convergent & divergent boundaries
•  At least one plate must have basaltic oceanic crust
–  Factors contributing to solid rock melting
•  Thermal gradient ⇒
Deeper is hotter
•  Friction
⇒ Subducting slab ⇔ country rock
•  Addition of water ⇒ Under-sea subduction trenches
•  Folded mountains
–  Occur primarily at convergent boundaries
•  Both plates must have granitic continental crust
Plate Motion Effects: Earthquakes
•  Divergent tectonic plate boundaries
–  All activity is near the Earth’s surface
•  Virtually all earthquakes are shallow
–  Most rock is relatively warm & soft
•  Absence of brittle rock reduces earthquake strength
•  Convergent tectonic plate boundaries
–  Ocean – ocean boundaries
•  Deep & strong earthquakes are very common
–  Ocean – continent boundaries
•  All depths & strong earthquakes are very common
•  Transform tectonic plate boundaries
–  Ocean – ocean boundaries
•  Absence of brittle rock reduces earthquake strength
–  Ocean – ocean boundaries
•  Presence of brittle rock increases earthquake strength
Plate Motion Effects: Geography
•  Continent ⇔ ocean configuration very dynamic
–  Three probable Pangaea episodes
•  All major landmasses gather into one supercontinent
•  Remaining 70% of Earth’s surface is one super-ocean
–  The present situation
•  Major continental landmasses are relatively stable
•  Major
ocean basins
are
very dynamic
–  Atlantic Ocean is increasing in size
–  Pacific Ocean is decreasing in size
–  Thrust faulting is also very common
•  Significant crustal shortening
Earth’s Magnetic Field
•  Basic physical processes
–  Slow circulation of the liquid metallic outer core
–  Rapid axial rotation of once per day
•  Basic
properties
–  Combined magnetic field of many smaller “cells”
–  Reverses on average ~ 0.5 million years
•  May be in the initial stages of a reversal now
–  Not perfectly aligned with Earth’s rotational axis
•  True of almost every planet in the Solar System
•  Magnetic declination
–  Deviation of magnetic North [compass] away from true North
•  Magnetic inclination
–  Angle between Earth’s surface & Earth’s magnetic field lines
Visualizing Earth’s Magnetic Field
Earth’s Magnetosphere
Visualizing Earth’s Magnetosphere
•  Basic physical processes
–  Earth’s relatively strong magnetic field
–  The
ever-changing
solar wind
•  Ionized hydrogen atoms
•  This is an electric current
Free protons & electrons
Generates a magnetic field
–  Strong interaction between two magnetic fields
•  Basic
properties
–  Earth’s magnetosphere shaped like a teardrop
•  Blunt side faces Sun, pointed side faces opposite Sun
–  Solar wind gusts produce striking effects
•  Geomagnetic storms
Disrupt radio signals
–  Occasionally strong enough to disrupt electric power distribution
•  Aurorae
Ionize atmospheric atoms
–  Occasionally strong enough to be seen in Florida & Texas
Aurora Australis From Space
So-Called “Greenhouse” Effect
Earth’s 3-D Atmospheric Circulation
Earth’s Vertical Atmospheric Structure
Terrestrial Planetary Atmospheres
•  Venus
•  Volcanic outgassing
–  ~100 times more atmosphere than Earth
–  ~ 96.5% CO2 & ~3.5% N2
–  Venus
•  Abundant with no oceans to assimilate gases
•  Runaway global warming
•  Earth
–  Very large amount of CO2 &
relatively close to
the Sun
–  Earth
•  Abundant with
–  ~ 78% N2 & ~21% O2
oceans to assimilate gases
–  Mars
•  Moderate global warming
–  Very small amount of CO2 & moderately close to the Sun
•  Mars
with no oceans to assimilate gases
–  Very common in the young Solar System
•  Minimal global warming
relatively far from
•  Absent
•  Comet impacts
–  ~100 times less atmosphere than Earth
–  ~ 95.3% CO2 & ~2.7% N2
–  Very small amount of CO2 &
Source of Planetary Atmospheres
the Sun
Growth of Earth’s Atmospheric O2
–  Very
rare
in today’s Solar System
Human Population & the Biosphere
•  Earth’s rapidly increasing human population
–  Burning fossil fuels returns CO2 to the atmosphere
•  General upward trend
Increasing use of fossil fuels
•  Seasonal fluctuations
Summer CO2 uptake by plants
–  Removing forest cover (deforestation)
•  Reduces CO2 uptake
–  Partially offset by ocean absorption
•  Radically changes local climate
–  Much hotter & much drier
–  Body heat contributes to “urban heat island” effect
•  Only recognized very recently
Earth’s Growing Human Population
Northern Hemisphere CO2 Increase
Earth’s Changing Temperatures
Important Concepts
• 
–  Geosp., hydrosp., atmosp. & biosp.
• 
•  Location of continents & ocean basins
•  Volcanic & earthquake activity
Earth’s environmental spheres
The rock cycle
• 
•  Rotation & outer core convection
•  Magma as Earth’s initial condition
•  Geomagnetic field reversals
–  Three basic rock types
–  Generation of the magnetosphere
•  Igneous, sedimentary & metamorphic
• 
•  Interactions with the solar wind
•  Aurora Borealis & Aurora Australis
Earth’s internal structure
–  Chemical & physical classifications
–  Interactions between temp. & pressure
–  Information from seismic waves
• 
Plate tectonics
–  Driven by mantle convection
–  Plate boundary types & properties
•  Convergent, divergent & transform
–  Effects of plate tectonic activity
Terrestrial planetary atmospheres
–  Venus, Earth & Mars compared
•  Atmospheric gases & amounts
•  Closeness to the Sun
•  Compressional & transverse waves
•  Surface & body waves
• 
Earth’s magnetic field
–  Basic causes
–  Five materials & five processes
–  Atmospheric structure & circulation
• 
Earth’s human population
–  Rapid growth in numbers
–  Use of fossil fuels
•  CO2 returned to Earth’s atmosphere
•  Global warming & ozone depletion
Earth’s Antarctic Ozone Hole