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Earth: Portrait of a Planet
 

Earth: Portrait of a Planet

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    Earth: Portrait of a Planet Earth: Portrait of a Planet Presentation Transcript

    • Chapter 2 Journey to the Center of the EarthEarth: Portrait of a Planet, 4th edition, by Stephen Marshak © 2011, W. W. Norton Chapter 2: Journey to the Center of the Earth
    • Journey to the Center of the EarthPrepared by:Ronald Parker, Senior Geologist Parker,Fronterra Geosciences,Denver, Colorado Earth: Portrait of a Planet, 4th edition, by Stephen Marshak © 2011, W. W. Norton Chapter 2: Journey to the Center of the Earth
    • Earth’s Surface Our experience with Earth is limited to its surface. Dramatic elevation changes—mountains, canyons—are tiny “scratches” on this surface. Our Earth is much more vast and complex than the surface suggests. Fig. 2.0Earth: Portrait of a Planet, 4th edition, by Stephen Marshak © 2011, W. W. Norton Chapter 2: Journey to the Center of the Earth
    • A Journey through Space A probe to Earth from an extra-solar planet, would:  Traverse the profound vacuum of interstellar space.  Encounter the diffuse edge of the Solar System, which is: Defined by the faint pull of the Sun’s gravity. Populated by fragments of ice and rock, the Oort Cloud. 50,000 AUs from the Sun. (One AU, an astronomical unit, is the distance between Earth and the Sun, 93 million miles).Earth: Portrait of a Planet, 4th edition, by Stephen Marshak © 2011, W. W. Norton Chapter 2: Journey to the Center of the Earth
    • The Solar System The boundary of the heliosphere is 200 AU from the Sun.  This is the outer reach of the solar wind. The Kuiper Belt is an diffuse band of icy objects.  Some are up to 1,200 km across.  Comets originate here.  Neptune is the inner edge. Neptune’s orbit defines interplanetary space. Fig. 2.1Earth: Portrait of a Planet, 4th edition, by Stephen Marshak © 2011, W. W. Norton Chapter 2: Journey to the Center of the Earth
    • The Planets All planetary orbits lie on the same plane (the ecliptic). Eight planets constitute the Solar System.  Outer ice-giant planets (Neptune and Uranus)  Gas-giant planets (Saturn and Jupiter)  Terrestrial planets (Mars, Earth, Venus, and Mercury) The asteroid belt lies between Jupiter and Mars. Fig. 2.5Earth: Portrait of a Planet, 4th edition, by Stephen Marshak © 2011, W. W. Norton Chapter 2: Journey to the Center of the Earth
    • Asteroids Asteroids: small bodies of rock or metal orbiting the Sun.  Planetesimals that were never part of a larger planet.  Fragmented larger planetesimals.  Most occur in a belt between Jupiter and Mars.  Range in size. Up to 30 km across Millions >1km in diameter Too small to be reshaped by gravity  Asteroids can strike Earth. Fig. Bx2.1aEarth: Portrait of a Planet, 4th edition, by Stephen Marshak © 2011, W. W. Norton Chapter 2: Journey to the Center of the Earth
    • Comets Comets: icy planetesimals that orbit the Sun.  They traverse highly elliptical orbits around the Sun.  When approaching the Sun, they develop a long coma (tail). The tail is comprised of evaporating gas and dust. The tail always points away from the Sun.  Short-period comets originate in the Kuiper Belt.  Longer period comets may derive from the Oort Cloud.  “Dirty snowballs” made of:  H2O, CO2, CH4, NH3 Other volatiles Organic compounds Dust  Comets can strike Earth. Fig. Bx2.1bEarth: Portrait of a Planet, 4th edition, by Stephen Marshak © 2011, W. W. Norton Chapter 2: Journey to the Center of the Earth
    • Magnetic Field Space visitors would notice Earth’s magnetic field. Earth’s magnetic field is like a giant dipole bar magnet.  The field has north and south ends.  The field grows weaker with distance.  The magnetic flux is directional. Flows from S pole to N pole along the bar magnet Flows from N to S along field lines outside the bar Fig. 2.3aEarth: Portrait of a Planet, 4th edition, by Stephen Marshak © 2011, W. W. Norton Chapter 2: Journey to the Center of the Earth
    • Magnetic Field Earth’s magnetic field is like a giant dipole bar magnet. The N pole of the bar is near Earth’s geographic S pole.  A compass needle aligns with the field lines.  The N compass arrow points to the bar magnet S pole. Opposites attract. Magnetic field lines:  Extend into space.  Weaken with distance.  Form a shield around Earth (magnetosphere). Fig. 2.3bEarth: Portrait of a Planet, 4th edition, by Stephen Marshak © 2011, W. W. Norton Chapter 2: Journey to the Center of the Earth
    • Magnetic Field The solar wind distorts the magnetosphere.  Shaped like a teardrop  Deflects most of the solar wind, protecting Earth The strong magnetic field of the Van Allen belts arrests deadly cosmic radiation. Fig. 2.3cEarth: Portrait of a Planet, 4th edition, by Stephen Marshak © 2011, W. W. Norton Chapter 2: Journey to the Center of the Earth
    • Magnetic Field The magnetic field is revealed by spectacular aurorae.  Some charged particles make it past the Van Allen belts.  These are channeled along magnetic field lines.  They cause atmospheric gases in polar regions to glow. Northern lights: aurora borealis. Southern lights: aurora australis. Fig. 2.3dEarth: Portrait of a Planet, 4th edition, by Stephen Marshak © 2011, W. W. Norton Chapter 2: Journey to the Center of the Earth
    • The Atmosphere Our atmosphere is mostly nitrogen (N2) and oxygen (O2). The remaining gases, (totaling less than 1%) include:  Argon (0.93%), carbon dioxide (0.039%), neon (0.0018%)  Other, less common, gases (helium, methane, krypton). The atmosphere thins away from Earth. Atmospheric layers have distinct characteristics.  Pressure, temperature, density, moisture composition Fig. 2.4a,bEarth: Portrait of a Planet, 4th edition, by Stephen Marshak © 2011, W. W. Norton Chapter 2: Journey to the Center of the Earth
    • The Atmosphere The atmosphere is more dense closer to Earth. Sea-level atmospheric pressure:  14.7 pounds per square inch (psi)  1.01 bar With increasing elevation:  Pressure decreases.  Density decreases.  Oxygen content decreases. Fig. 2.4cEarth: Portrait of a Planet, 4th edition, by Stephen Marshak © 2011, W. W. Norton Chapter 2: Journey to the Center of the Earth
    • The Atmosphere Atmospheric layers are separated by pauses.  Troposphere (0–11 km): The lower mixing layer. Weather is confined to this layer. Temperature decreases upward.  Stratosphere (12–47 km): No mixing occurs. Temperature increases upward.  Mesosphere (47–82 km): Temperature decreases upward.  Thermosphere (82 km+): Outermost layer. Temperature increases upward. Fig. 2.4dEarth: Portrait of a Planet, 4th edition, by Stephen Marshak © 2011, W. W. Norton Chapter 2: Journey to the Center of the Earth
    • The Earth System Orbiting around Earth, space visitors would notice:  Atmosphere—the gaseous envelope.  Hydrosphere—the blue liquid water.  Cryosphere—the frozen world.  Biosphere—the wealth of life.  Lithosphere—the solid Earth. Interaction of these components interactions, comprises the Earth System. Earth is in the habitable zone. Only Earth has liquid water, and hence, life. Fig. 2.2Earth: Portrait of a Planet, 4th edition, by Stephen Marshak © 2011, W. W. Norton Chapter 2: Journey to the Center of the Earth
    • Earth’s Surface Land and water are the most prominent surface features. Icecaps and living organisms are also in evidence. Fig. 2.6Earth: Portrait of a Planet, 4th edition, by Stephen Marshak © 2011, W. W. Norton Chapter 2: Journey to the Center of the Earth
    • Hypsometric Curve Most land lies within 1 km of sea level. Most ocean floors are close to 5 km in depth. Extreme highs or lows of depth or height are rare. The two dominant “levels” reflect continental vs. oceanic crust. Fig. 2.7Earth: Portrait of a Planet, 4th edition, by Stephen Marshak © 2011, W. W. Norton Chapter 2: Journey to the Center of the Earth
    • Elemental Composition 91.2% of Earth is comprised of just four elements.  Iron (Fe)—32.1%  Oxygen (O)—30.1%  Silicon (Si)—15.1%  Magnesium (Mg)—13.9% The remaining eighty-eight are naturally occurring elements: 8.8% These ratios differ for Earth’s crust. Fig. 2.8Earth: Portrait of a Planet, 4th edition, by Stephen Marshak © 2011, W. W. Norton Chapter 2: Journey to the Center of the Earth
    • Earth Materials Elements combine in a variety of Earth materials.  Organic compounds—carbon-containing compounds. Most are residue from once-living creatures. These include wood, peat, lignite, coal, and oil. Geologically rare (organic in contact with oxygen).Earth: Portrait of a Planet, 4th edition, by Stephen Marshak © 2011, W. W. Norton Chapter 2: Journey to the Center of the Earth
    • Earth Materials Elements combine in a variety of Earth materials.  Minerals—naturally-occurring crystalline solids. Crystal—a single coherent mineral with geometric faces. Grain—an irregularly shaped fragment of a larger crystal. Minerals comprise rocks and, therefore, most of the earth.  Glasses—noncrystalline solids. Glasses form by rapid cooling—too fast for crystal growth.Earth: Portrait of a Planet, 4th edition, by Stephen Marshak © 2011, W. W. Norton Chapter 2: Journey to the Center of the Earth
    • Earth Materials Elements combine in a variety of Earth materials.  Rocks—aggregates of minerals, grains, and/or glass. Igneous—cooled from a liquid (melt). Sedimentary—debris cemented from preexisting rock. Metamorphic—rock altered by pressure and temperature.  Rocks may be made of a single mineral.Earth: Portrait of a Planet, 4th edition, by Stephen Marshak © 2011, W. W. Norton Chapter 2: Journey to the Center of the Earth
    • Earth Materials Elements combine in a variety of Earth materials.  Sediment—an accumulation of loose mineral grains. Weathered and eroded from preexisting rocks. Precipitated from evaporating water.  Metals—solids composed of metal atoms (Al, Fe, Cu, Sn). Metals have high density, are shiny and conduct electricity.Earth: Portrait of a Planet, 4th edition, by Stephen Marshak © 2011, W. W. Norton Chapter 2: Journey to the Center of the Earth
    • Earth Materials Elements combine in a variety of Earth materials.  Melts—rocks that have been heated to a liquid. Magma—molten rock beneath the surface. Lava—molten rock at the surface.  Volatiles—materials that turn into gas at the surface. H2O, CO2, CH4 and SO2 Volatiles are released from volcanic eruption.Earth: Portrait of a Planet, 4th edition, by Stephen Marshak © 2011, W. W. Norton Chapter 2: Journey to the Center of the Earth
    • Earth Materials Most rocks on Earth are silicates (based on Si and O). There are four fundamental silicate igneous rock types.  Vary by silica (SiO ) to iron (Fe) and magnesium (Mg). 4 Felsic—most Si-rich, Fe and Mg-poor. Ex: Granite Intermediate Mafic Ultramafic—most Si-poor, Fe and Mg-rich. Ex: PeridotiteEarth: Portrait of a Planet, 4th edition, by Stephen Marshak © 2011, W. W. Norton Chapter 2: Journey to the Center of the Earth
    • A Layered Earth How do we know that the Earth has a layered interior? Early speculations sought to explain:  The source of lava.  Gem and mineral enrichment.  Spring waters.  Earthquakes. Early guesses were wrong.  Open caverns to the interior  Flowing lava, air, water Fig. 2.9Earth: Portrait of a Planet, 4th edition, by Stephen Marshak © 2011, W. W. Norton Chapter 2: Journey to the Center of the Earth
    • A Layered Earth The first key to understanding Earth’s interior: density.  A plumb bob is deflected by a nearby mountain mass.  Degree of deflection can be used to calculate Earth’s mass.  The density from this method (4.5 g/cm3) is much higher than the density of the thin outer crust (2.5 g/cm3).  This suggests that density must increase with depth. Fig. 2.10Earth: Portrait of a Planet, 4th edition, by Stephen Marshak © 2011, W. W. Norton Chapter 2: Journey to the Center of the Earth
    • A Layered Earth The first key to understanding Earth’s interior: density.  In 1896, Emil Wiechert made important contributions. He determined that metal must be present in Earth’s interior. He deduced that the metal must occur at the Earth’s center.  We now know he was correct.  His ideas led to a model: Earth is like an egg. Thin, light crust (eggshell) Thicker, more dense mantle (eggwhite) Innermost, very dense core (yolk)  Other density observations: The land doesn’t have large tides, hence Earth must be solid. Fig. 2.11Earth: Portrait of a Planet, 4th edition, by Stephen Marshak © 2011, W. W. Norton Chapter 2: Journey to the Center of the Earth
    • A Layered Earth Earthquakes: seismic energy from fault motion.  Seismic waves provide insight into Earth’s interior. Seismic wave velocities change with density. We can determine the depth of seismic velocity changes. Hence, we can tell where densities change in Earth’s interior. Fig. 2.12Earth: Portrait of a Planet, 4th edition, by Stephen Marshak © 2011, W. W. Norton Chapter 2: Journey to the Center of the Earth
    • A Layered Earth Changes with depth.  Pressure (P) The weight of overlying rock increases with depth.  Temperature (T) Heat is generated in Earth’s interior.  T increases with depth. Geothermal gradient  The rate of T changes with depth.  The geothermal gradient varies. High of 50°C per km Low of 15°C per km Determined by tectonic setting Fig. 2.13 Earth: Portrait of a Planet, 4th edition, by Stephen Marshak © 2011, W. W. Norton Chapter 2: Journey to the Center of the Earth
    • Layer Compositions Geologists strived to understand the nature of the layers.  Studied meteorites as analogues for core and mantle.  Conducted laboratory experiments. Density measurements of rocks from the interior Characteristics of mantle-derived rocks and minerals Determined high P and T stability field of rocks and minerals Fig. Bx.2.2cEarth: Portrait of a Planet, 4th edition, by Stephen Marshak © 2011, W. W. Norton Chapter 2: Journey to the Center of the Earth
    • Layer Compositions End result of a century of investigation?  We know much about the nature of Earth’s interior.  This knowledge continues to evolve. Earth’s layers consist of the crust, upper, transitional, and lower mantles, and liquid outer and solid inner cores. Much complexity characterizes even these layers. Geology at a Glance Earth: Portrait of a Planet, 4th edition, by Stephen Marshak © 2011, W. W. Norton Chapter 2: Journey to the Center of the Earth
    • The Crust The outermost “skin” of our planet; highly variable.  Thickest under mountain ranges (70 km or 40 miles).  Thinnest under mid-ocean ridges (7 km or 4 miles). Relatively as thick as the membrane of a toy balloon. The Mohorovičić discontinuity (Moho) is the base.  Seismic velocity change between crust and upper mantle.  The crust is the upper part of a tectonic plate. Fig. 2.14aEarth: Portrait of a Planet, 4th edition, by Stephen Marshak © 2011, W. W. Norton Chapter 2: Journey to the Center of the Earth
    • The Crust There are two kinds of crust: continental and oceanic.  Continental crust underlies the continents. Average density of ~2.7 g/cm3 Average thickness 35–40 km Felsic (granitic) to intermediate in composition.  Oceanic crust underlies the ocean basins. Average density of ~3.0 g/cm3 Average thickness 7–10 km Mafic (basaltic and gabbroic) in composition. Fig. 2.14aEarth: Portrait of a Planet, 4th edition, by Stephen Marshak © 2011, W. W. Norton Chapter 2: Journey to the Center of the Earth
    • The Crust There are two kinds of crust: continental and oceanic. Crustal density controls surface position.  Continental crust Less dense: “floats higher”  Oceanic crust More dense: “floats lower” Fig. 2.14cEarth: Portrait of a Planet, 4th edition, by Stephen Marshak © 2011, W. W. Norton Chapter 2: Journey to the Center of the Earth
    • Crustal Composition 98.5% of the crust is comprised of just eight elements. Oxygen is the most abundant element in the crust.  This reflects the importance of silicate (SiO4) minerals.  Oxygen is large. It occupies ~93% of crustal volume. Fig. 2.15Earth: Portrait of a Planet, 4th edition, by Stephen Marshak © 2011, W. W. Norton Chapter 2: Journey to the Center of the Earth
    • The Mantle Solid rock, 2,885 km thick, 82% of Earth’s volume. The mantle is entirely the ultramafic rock peridotite. Convection below 100 km mixes the mantle.  Like oatmeal on a stove: hot rises, cold sinks.  Convection aids tectonic plate motion. Upper, transitional, and lower. Fig. Bx2.3c Geology at a GlanceEarth: Portrait of a Planet, 4th edition, by Stephen Marshak © 2011, W. W. Norton Chapter 2: Journey to the Center of the Earth
    • The Core An iron-rich sphere with a radius of 3,471 km. Seismic waves segregate two radically different parts.  The outer core is liquid; inner core solid.  Outer core Liquid iron-nickel-sulfur 2,255 km thick Density is 10–12 g/cm3  Inner core Solid iron-nickel alloy Radius of 1,220 km Density is 13 g/cm3 Outer core flow generates Earth’s magnetic field. Geology at a GlanceEarth: Portrait of a Planet, 4th edition, by Stephen Marshak © 2011, W. W. Norton Chapter 2: Journey to the Center of the Earth
    • Summarizing Earth’s Layers Earth has a layered interior.  Crust Continental Oceanic  Mantle Upper Transitional Lower  Core Outer—liquid Inner—solid These layers are subdivided on the basis of seismic waves. Fig. 2.14bEarth: Portrait of a Planet, 4th edition, by Stephen Marshak © 2011, W. W. Norton Chapter 2: Journey to the Center of the Earth
    • Lithosphere-Asthenosphere We can also regard layering based on rock strength.  Lithosphere—the outermost 100–150 km of Earth. Behaves rigidly, as a nonflowing material. Comprised of two components: crust and upper mantle. This is the material that makes up tectonic plates.  Asthenosphere—upper mantle below the lithosphere. Shallow under oceanic lithosphere; deeper under continental. Flows as a soft solid. Fig. 2.16Earth: Portrait of a Planet, 4th edition, by Stephen Marshak © 2011, W. W. Norton Chapter 2: Journey to the Center of the Earth
    • Useful Web Resources NASA Solar System Exploration  http://solarsystem.nasa.gov/index.cfm AGU Geomagnetism and Paleomagnetism  http://www.agu.org/sections/geomag/background.html NOAA Weather and Atmosphere  http://www.education.noaa.gov/Weather_and_Atmosphere/ USGS Earthquake Hazards Program  http://earthquake.usgs.gov/earthquakes/ NESTA Structure of the Interior of the Earth  http://www.windows2universe.org/earth/Interior_Structure/interior.html Earth: Portrait of a Planet, 4th edition, by Stephen Marshak © 2011, W. W. Norton Chapter 2: Journey to the Center of the Earth
    • Photo CreditsEarth: Portrait of a Planet, 4th edition, by Stephen Marshak © 2011, W. W. Norton Chapter 2: Journey to the Center of the Earth
    • W. W. Norton & Company Independent and Employee-Owned This concludes the Norton Media Library PowerPoint Slide Set for Chapter 2 Earth: Portrait of a Planet 4th edition (2011) by Stephen Marshak Powerpoint slides prepared by Ronald L. Parker Senior Geologist, Fronterra Geosciences, Denver, ColoradoEarth: Portrait of a Planet, 4th edition, by Stephen Marshak © 2011, W. W. Norton Chapter 2: Journey to the Center of the Earth