Transcript Chapter 9: Our Living Earth PowerPoint

9. Our Living Earth
• Earth’s
atmosphere, oceans & surface
• Earth’s
interior & earthquakes
• Earth’s
plate tectonics activity
• Earth’s magnetic field & magnetosphere
• Earth’s
evolving atmosphere
• Earth’s
human population & biosphere
The Earth: A Portrait From Space
Earth Data (Table 9-1)
Earth From An Apollo Spacecraft
Earth’s Environmental Spheres
• Earth’s
spheres
– Geosphere
– Hydrosphere
– Atmosphere
– Biosphere
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
Rocks
• Definition
– 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
• 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
Rock Cycle
Magma: Source of 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
Some Common Igneous Rocks
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
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
Foliated Metamorphic Rocks: Gneiss
Oregon’s Metamorphic Environment
Portland
Astoria
Earth’s “Chemical” Differentiation
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
The focus is also called the hypocenter
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
Usually ! ! !
– Varieties
• Compressional waves
• Transverse
waves
Sideways jolting
Up & down jiggling
Compressional & Transverse Waves
Compressional Seismic Waves
Transverse Seismic Waves
Body Seismic Waves
Surface Seismic Waves
Seismicity & Earth’s Internal Structure
Plate Tectonics
• Tectonic plates = Lithospheric plates
– Rigid & brittle
• “Glide” over the asthenosphere
– Sizes vary greatly
• Micro plates
Juan de Fuca plate
• Macro plates
Pacific
plate
• Three kinds of tectonic plates
– Oceanic
plates
Basaltic composition
– Continental plates
Granitic composition
– Composite
Both basalt & granite
plates
Mantle Convection & Plate Motion
• Thermal gradient: Hotter at core than at crust
– Results in a density gradient
• Heat sources
– Planetesimal impact
Dominant as a protoplanet
– Radioactive decay
Ongoing exponential decay
– Gravitational collapse
Minimal as a protoplanet
• Point of origin
– Thought to be the core-mantle boundary
• Shape
– Elongated “curtains” of rising material
A Model of Mantle Convection
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: 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: 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
• Friction
• Addition of water
⇒
Deeper is hotter
⇒ Subducting slab ⇔ country rock
⇒ Under-sea subduction trenches
• Folded mountains
– Occur primarily at convergent boundaries
• Both plates must have granitic continental crust
– Thrust faulting is also very common
• Significant crustal shortening
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
– Atlantic Ocean is increasing in size
– Pacific Ocean is decreasing in size
very dynamic
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
• 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
Visualizing Earth’s Magnetosphere
Aurora Australis From Space
So-Called “Greenhouse” Effect
Earth’s 3-D Atmospheric Circulation
Earth’s Vertical Atmospheric Structure
Terrestrial Planetary Atmospheres
• Venus
– ~100 times more atmosphere than Earth
– ~ 96.5% CO2 & ~3.5% N2
• Runaway global warming
• Earth
– Very large amount of CO2 &
relatively close to
the Sun
– ~ 78% N2 & ~21% O2
• Moderate global warming
• Mars
– Very small amount of CO2 & moderately close to the Sun
– ~100 times less atmosphere than Earth
– ~ 95.3% CO2 & ~2.7% N2
• Minimal global warming
– Very small amount of CO2 &
relatively far from
the Sun
Source of Planetary Atmospheres
• Volcanic outgassing
– Venus
• Abundant with no oceans to assimilate gases
– Earth
• Abundant with
oceans to assimilate gases
– Mars
• Absent
with no oceans to assimilate gases
• Comet impacts
– Very common in the young Solar System
– Very
rare
in today’s Solar System
Growth of Earth’s Atmospheric O2
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
Earth’s Antarctic Ozone Hole
Important Concepts
•
– Geosp., hydrosp., atmosp. & biosp.
•
• Location of continents & ocean basins
• Volcanic & earthquake activity
Earth’s environmental spheres
The rock cycle
•
– Basic causes
– Five materials & five processes
• Rotation & outer core convection
• Geomagnetic field reversals
• Magma as Earth’s initial condition
– 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
– 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