The Earth: A Portrait From Space. 9. Our Living Earth. Rocks

Transcription

1 9. Our Living Earth The Earth: A Portrait From Space 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 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 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 one mineral Other rocks have many crystals of two or more 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

2 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

3 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 Earth s Chemical Differentiation Astoria 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

4 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 Body Seismic Waves Compressional Seismic Waves Transverse Seismic Waves

5 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

6 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

7 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

8 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 Aurora Boralis: Bear Lake, Alaska Aurora borelis from Fairbanks, Alaska Aurora Borealis: Scotland 2014/02/28 Aurora Borealis: Finland

9 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% CO 2 & ~3.5% N 2 Runaway global warming Very large amount of CO 2 & relatively close to the Sun Earth ~ 78% N 2 + ~21% O 2 + ~1% Ar Moderate global warming Very small amount of CO 2 & moderately close to the Sun Mars ~100 times less atmosphere than Earth ~ 95.3% CO 2 & ~2.7% N 2 Minimal global warming Very small amount of CO 2 & 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 O 2

10 Human Population & the Biosphere Earth s rapidly increasing human population Burning fossil fuels returns CO 2 to the atmosphere General upward trend Increasing use of fossil fuels Seasonal fluctuations Summer CO 2 uptake by plants Removing forest cover (deforestation) Reduces CO 2 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 CO 2 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 Important Concepts 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 CO 2 returned to Earth s atmosphere Global warming & ozone depletion