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The earliest material found in the Solar System is dated to 4.5672±0.0006 by] therefore, it is inferred that the Earth must have been formed by accretion around this time. By 4.54±0.04 by the …

The earliest material found in the Solar System is dated to 4.5672±0.0006 by] therefore, it is inferred that the Earth must have been formed by accretion around this time. By 4.54±0.04 by the primordial Earth had formed. The formation and evolution of the Solar System bodies occurred in tandem with the Sun. In theory a solar nebula partitions a volume out of a molecular cloud by gravitational collapse, which begins to spin and flatten into a circumstellar disk, and then the planets
grow out of that in tandem with the star. A nebula contains gas, ice grains and dust

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  • 1. Chapter 2 Journey to the Center of the Earth LECTURE OUTLINE earth Portrait of a Planet Third Edition ©2008 W. W. Norton & Company, Inc. Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 2: Journey to the Center of the Earth
  • 2. Journey to the Center of the Earth Prepared by Ronald Parker Earlham College Department of Geosciences Richmond, Indiana
  • 3. Earth’s Surface Our experience with Earth is limited to its surface.  Yet Earth has a complicated interior.  Earth is characterized by…   An internally generated magnetic field.  Solid and liquid surfaces.  A gaseous envelope.  A layered interior. Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 2: Journey to the Center of the Earth
  • 4. The Solar System  Human perceptions have changed.  Early history – Planets as moving lights.  1600s – 1st telescopes saw hazy spheres.  Today – A complex, evolving system. Structure History Space probes have photographed and analyzed planets.  Scientists have hypothesized likely origins of the solar system.  Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 2: Journey to the Center of the Earth
  • 5. Earth and the Solar System  What would solar system visitors notice?  Magnetic field.  Atmosphere.  Surface features. Continents. Oceans. Polar ice caps. Evidence of humanity? Structures. Dams. Great Wall of China. Cities. Roads / canals. Electric lights. Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 2: Journey to the Center of the Earth
  • 6. The Celestial Neighborhood     Interstellar space: a vacuum with a virtual absence of matter. The amount of matter greatly increases approaching the Sun. The Sun ejects matter outward into space as the solar wind. Solar wind:  Magnetically charged particles.  Stream outward in all directions.  Consists of…  Protons (+ charge). Electrons (– charge). A small percentage of the solar wind impinges upon Earth. Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 2: Journey to the Center of the Earth
  • 7. Magnetic Field     The Earth has a prominent dipolar magnetic field. Like a bar magnet, the field has north and south ends. Magnetic flux has a direction that flows N to S. Magnetic field lines…  Extend into space.  Weaken with distance.  Create a shield around Earth (the magnetosphere). Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 2: Journey to the Center of the Earth
  • 8. The Van Allen Belts   The solar wind is deflected by the magnetosphere. Near the Earth, the stronger magnetic field forms the Van Allen belts, which arrest deadly cosmic radiation. Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 2: Journey to the Center of the Earth
  • 9. Aurorae  Some ions escape Van Allen belts.  These ions are pulled to the magnetic poles.  The ions create light in the upper atmosphere.  Spectacular aurora follow solar flares.  Aurora borealis – Northern lights.  Aurora australis – Southern lights. Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 2: Journey to the Center of the Earth
  • 10. The Atmosphere Earth has a well developed atmosphere.  Thus, Earth is unique among the terrestrial planets.  Densest at sea-level, the atmosphere thins upward.  Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 2: Journey to the Center of the Earth
  • 11. The Atmosphere  The atmosphere is mostly nitrogen. Oxygen was absent from the atmosphere before 2.5 Ga.  Other gases include:  Argon (Ar) Carbon dioxide (CO2) Carbon monoxide (CO) Methane (CH4) Neon (Ne) Ozone (O3) Sulfur dioxide (SO2) Chlorofluorocarbons (CFCs) Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 2: Journey to the Center of the Earth
  • 12. The Atmosphere   99% of atmosphere is below 50 km, the rest is between 50 and 500 km. The atmosphere is layered.  Troposphere (0-11 km). Mixing layer. Weather is limited to this layer.  Tropopause (11-12 km).  Stratosphere (12-30 km).  Sea-level atmospheric pressure.  14.7 pounds per square inch (psi).  1.0 bar. Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 2: Journey to the Center of the Earth
  • 13. Surface Features   Earth’s surface is dominated by water and land. Water is a part of the hydrosphere.  Surface water  Ground water.  Glacial ice.  Impact craters occur rarely on Earth.  Removed by weathering and erosion.  Unlike other planets in the solar system. Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 2: Journey to the Center of the Earth
  • 14. Surface Features  Earth’s surface reveals high continents and low ocean basins.  Position due to the differing buoyancy of each type of crust. Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 2: Journey to the Center of the Earth
  • 15. Hypsometric Curve     Most land lies within 1 km of sea level. Most ocean floors are close to 5 km depth. Extremes of depth or height are rare. The 2 dominant “levels” reflect continental vs. oceanic crust. Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 2: Journey to the Center of the Earth
  • 16. Elemental Composition  ~Ninety percent of Earth is comprised of 4 elements.  Iron (Fe) ~35%  Oxygen (O) ~30%  Silicon (Si) ~15%  Magnesium (Mg) ~10%  The remaining 88 naturally occurring elements?  Form ~10% of Earth. Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 2: Journey to the Center of the Earth
  • 17. Earth Materials  Elements combine in a variety of Earth materials.  Organic compounds – Carbon-containing compounds. Most are residue from once-living creatures. Include wood, peat, lignite, coal, and oil. Geologically rare (decomposes in contact with oxygen). Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 2: Journey to the Center of the Earth
  • 18. Earth Materials  Elements combine in a variety of Earth materials.  Minerals – Inorganic crystalline solids. Comprise rocks and, hence, most of the Earth. Most rocks on Earth are silicates (based on Si and O).  Glasses – Non-crystalline mineral-like matter.  Rocks – Aggregates of minerals. There are many types. Igneous – Cooled from a liquid (melt). Sedimentary – Debris cemented from pre-existing rock. Metamorphic – Rock altered by pressure and temperature. Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 2: Journey to the Center of the Earth
  • 19. Earth Materials Metals – Solids made of metallic elements.  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, 3rd edition, by Stephen Marshak Chapter 2: Journey to the Center of the Earth
  • 20. A Layered Earth We live on the thin outer skin of Earth.  Early perceptions about Earth’s interior were wrong.   Open caverns filled with magma, water, and air.  Furnaces and flames.  We now know that Earth is comprised of layers.  The Crust.  The Mantle.  The Core. Outer Core. Inner Core. Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 2: Journey to the Center of the Earth
  • 21. A Layered Earth Several clues indicate a layered structure.  Density – Plumb bob deflection estimates density.   Average density greater than surface density.  Density must increase with depth.  Shape – A rotating sphere requires centered mass.  Mass away from center would result in a flattened disk.  Solid interior - Surface doesn’t undulate from tidal forces. Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 2: Journey to the Center of the Earth
  • 22. A Layered Earth  Earthquake clues - Earthquake energy transmitted as seismic waves that pass through Earth.  Seismic waves have been used to probe the interior.  Wave velocity changes with density. Velocity changes give depth of layer changes. Changes with depth.  Pressure.  Temperature. Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 2: Journey to the Center of the Earth
  • 23. Earth’s Interior Layers  Earth (and other planets) have layered interiors.  Crust Continental Oceanic  Mantle Upper Lower  Core Outer – Liquid Inner – Solid Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak © W. W. Norton Chapter 2: Journey to the Center of the Earth
  • 24. The Crust  The outermost “skin” of Earth with variable thickness.  Thickest under mountain ranges (70 km – 40 miles).  Thinnest under mid-ocean ridges (3 km – 2 miles).  The Mohorovicic discontinuity is the lower boundary.  Separates the crust from the upper mantle.  Discovered in 1909 by Andrija Mohorovicic.  Marked by a change in the velocity of seismic P waves. Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 2: Journey to the Center of the Earth
  • 25. Two Types of Crust  Continental crust – Underlies the continents.  Average rock density about 2.7 g/cm3.  Average thickness 35-40 km.  Granitic in composition.  Oceanic crust – Underlies the ocean basins.  Density about 3.0 g/cm3.  Avg. thickness 7-10 km.  Basaltic in composition. Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 2: Journey to the Center of the Earth
  • 26. Two Types of Crust  Crustal density controls surface position.  Continental crust Less dense; “floats higher.”  Oceanic crust More dense: “floats lower.” Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 2: Journey to the Center of the Earth
  • 27. Crustal Composition   98.5% of the crust is comprised of just 8 elements. Oxygen is (by far!) the most abundant element in the crust.  This reflects the importance of silicate (SiO4-based) minerals.  As a large atom, oxygen occupies ~93% of crustal volume. Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 2: Journey to the Center of the Earth
  • 28. Earth’s Mantle Solid rock layer between the crust and the core.  2,885 km thick, the mantle is 82% of Earth’s volume.  Mantle composition is the ultramafic rock peridotite.  Below ~100-150 km, the rock is hot enough to flow.  It convects: hot mantle rises, cold mantle sinks.  Three subdivisions: upper, transitional, and lower.  Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 2: Journey to the Center of the Earth
  • 29. The Core An iron-rich sphere with a radius of 3,471 km.  2 components with differing seismic wave behavior.   Outer core Liquid iron-nickel-sulfur 2,255 km thick Density – 10-12 g/cm3  Inner core Solid iron-nickel alloy Radius of 1,220 km. Density – 13 g/cm3  Flow in the outer core generates the magnetic field. Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 2: Journey to the Center of the Earth
  • 30. Lithosphere-Asthenosphere  Lithosphere – The outermost 100-150 km of Earth.  Behaves as a non-flowing, rigid material.  The material that moves as tectonic plates.  Made of 2 components: crust and upper mantle.  Asthenosphere – Upper mantle below lithosphere.  Shallower under oceanic lithosphere.  Deeper under continental lithosphere.  Flows as a soft solid. Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 2: Journey to the Center of the Earth
  • 31. Earth’s Interior Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 2: Journey to the Center of the Earth
  • 32. This concludes the Chapter 2 Journey to the Center of the Earth LECTURE OUTLINE earth Portrait of a Planet Third Edition ©2008 W. W. Norton & Company, Inc. Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 2: Journey to the Center of the Earth