9. our living earth
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9. Our Living Earth. Earth ’ satmosphere , oceans & surface Earth ’ sinterior & e arthquakes Earth’splate tectonics activity Earth ’ smagnetic field & magnetosphere Earth ’ sevolving atmosphere Earth ’ s human population & biosphere. The Earth: A Portrait From Space. - PowerPoint PPT PresentationTRANSCRIPT
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 Rock & metallic Earth materials– Hydrosphere Water as ice, liquid & humidity– Atmosphere ~78% nitrogen & ~21% oxygen– Biosphere 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 energyon one side
– Radiant heat in extremely large amounts leaveson 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 produces igneous rock– Weathering produces sediment– Lithification produces sedimentary rock– Metamorphism produces metamorphic rock– Melting 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 Remains of plants & animals
– Coal Fossilized fern leaves
• Clastic Broken rock & mineral fragments– Sandstone, shale & limestone
• Bioclastic Broken shell fragments– Coquina Limestone “fossil hash”
• Chemical Crystallization from water solution– Gypsum 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 EnvironmentPortland
Astoria
Earth’s “Chemical” Differentiation
Characterizing Earth’s Interior• Chemical composition Mineral composition
– Low density minerals Crust• Granite continents & basalt ocean basins
– Intermediate density minerals Mantle• Peridotite
– High density minerals Core• Iron & nickel
• Physical condition Solid / plastic / liquid– A function of temperature & pressure
• Temperature increases slowly with depth• Pressure increases rapidly with depth
– Solid Lithosphere Old & cool enough– Plastic Asthenosphere Lubricating layer– Solid Mantle Very slightly plastic– Liquid Outer core Temperature wins– Solid Inner core 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 P-waves Primary waves
• Transverse waves S-waves Secondary waves
• Surface waves– Source location: Epicenter
• Place of maximum surface shaking• Place directly above the focus Usually ! ! !
– Varieties• Compressional waves Sideways jolting• Transverse waves 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 plates Both basalt & granite
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 ⇒ 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
– 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 very dynamic
– Atlantic Ocean is increasing in size– Pacific Ocean is decreasing in size
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 Free protons & electrons
• This is an electric current 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– Very large amount of CO2 & relatively close to
the Sun• Earth
– ~ 78% N2 & ~21% O2• Moderate global warming
– Very small amount of CO2 & moderately close tothe Sun
• Mars– ~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
• Earth’s environmental spheres– Geosp., hydrosp., atmosp. & biosp.
• The rock cycle– Five materials & five processes
• Magma as Earth’s initial condition– Three basic rock types
• Igneous, sedimentary & metamorphic• Earth’s internal structure
– Chemical & physical classifications– Interactions between temp. & pressure– Information from seismic waves
• Compressional & transverse waves• Surface & body waves
• Plate tectonics– Driven by mantle convection– Plate boundary types & properties
• Convergent, divergent & transform– Effects of plate tectonic activity
• Location of continents & ocean basins• Volcanic & earthquake activity
• Earth’s magnetic field– Basic causes
• Rotation & outer core convection• Geomagnetic field reversals
– Generation of the magnetosphere• Interactions with the solar wind• Aurora Borealis & Aurora Australis
• Terrestrial planetary atmospheres– Venus, Earth & Mars compared
• Atmospheric gases & amounts• Closeness to the Sun
– 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
Important Concepts