Journey to the Center of the Earth

Prepared by

Ronald Parker
Earlham College Department of Geosciences
Richmond, Indiana
Earth’s Surface
Our experience with Earth is limited to its surface.
 Yet Earth has a complicated interior.
 Earth is ch...
The Solar System


Human perceptions have changed.
 Early history – Planets as moving lights.
 1600s – 1st telescopes s...
Earth and the Solar System


What would solar system visitors notice?
 Magnetic field.
 Atmosphere.
 Surface features....
The Celestial Neighborhood





Interstellar space: a vacuum with a virtual absence of matter.
The amount of matter gr...
Magnetic Field





The Earth has a prominent dipolar magnetic field.
Like a bar magnet, the field has north and south...
The Van Allen Belts



The solar wind is deflected by the magnetosphere.
Near the Earth, the stronger magnetic field for...
Aurorae


Some ions escape Van Allen belts.
 These ions are pulled to the magnetic poles.
 The ions create light in the...
The Atmosphere
Earth has a well developed atmosphere.
 Thus, Earth is unique among the terrestrial planets.
 Densest at ...
The Atmosphere


The atmosphere is mostly nitrogen.
Oxygen was absent from the atmosphere before 2.5 Ga.



Other gases ...
The Atmosphere




99% of atmosphere is below 50 km,
the rest is between 50 and 500 km.
The atmosphere is layered.
 Tro...
Surface Features



Earth’s surface is dominated by water and land.
Water is a part of the hydrosphere.
 Surface water
...
Surface Features


Earth’s surface reveals high continents and low ocean basins.



Position due to the differing buoyan...
Hypsometric Curve





Most land lies within 1 km of sea level.
Most ocean floors are close to 5 km depth.
Extremes of...
Elemental Composition


~Ninety percent of Earth is comprised of 4 elements.
 Iron (Fe) ~35%
 Oxygen (O) ~30%
 Silicon...
Earth Materials


Elements combine in a variety of Earth materials.
 Organic compounds – Carbon-containing compounds.

...
Earth Materials


Elements combine in a variety of Earth materials.
 Minerals – Inorganic crystalline solids.

Comprise...
Earth Materials
Metals – Solids made of metallic elements.
 Melts – Rocks that have been heated to a liquid.


 Magma –...
A Layered Earth
We live on the thin outer skin of Earth.
 Early perceptions about Earth’s interior were wrong.


 Open ...
A Layered Earth
Several clues indicate a layered structure.
 Density – Plumb bob deflection estimates density.


 Avera...
A Layered Earth


Earthquake clues - Earthquake energy transmitted
as seismic waves that pass through Earth.
 Seismic wa...
Earth’s Interior Layers


Earth (and other planets) have layered interiors.
 Crust

Continental
Oceanic
 Mantle

Upp...
The Crust


The outermost “skin” of Earth with variable thickness.
 Thickest under mountain ranges (70 km – 40 miles).
...
Two Types of Crust


Continental crust – Underlies the continents.
 Average rock density about 2.7 g/cm3.
 Average thic...
Two Types of Crust


Crustal density controls surface position.
 Continental crust

Less dense; “floats higher.”
 Ocea...
Crustal Composition



98.5% of the crust is comprised of just 8 elements.
Oxygen is (by far!) the most abundant element...
Earth’s Mantle
Solid rock layer between the crust and the core.
 2,885 km thick, the mantle is 82% of Earth’s volume.
 M...
The Core
An iron-rich sphere with a radius of 3,471 km.
 2 components with differing seismic wave behavior.


 Outer co...
Lithosphere-Asthenosphere


Lithosphere – The outermost 100-150 km of Earth.
 Behaves as a non-flowing, rigid material.
...
Earth’s Interior

Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak

Chapter 2: Journey to the Center of the Ea...
This concludes the
Chapter 2
Journey to the Center of the Earth

LECTURE OUTLINE

earth

Portrait of a Planet

Third Editi...
Op ch02 lecture_earth3
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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 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. 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. 2. Journey to the Center of the Earth Prepared by Ronald Parker Earlham College Department of Geosciences Richmond, Indiana
  3. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 31. Earth’s Interior Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 2: Journey to the Center of the Earth
  32. 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

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