Formation of Earth

1
Formation of Earth

• Birth of the Solar System
• Nebular Theory
• Nebula compresses
• Rotation flattens nebula
• Collapse into center formed solar nebula and
  finally, the sun
• Condensation formed planets, planetesimal, moons
  and asteroids during planetary accretion around
  4.6 billion years ago
• (Meteorites are iron-rich or rocky fragments left
  over from planetary accretion)

See Fig. 1.9 (a), (b) and (c)
http//www.psi.edu/projects/planets/planets.html
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Orion Nebula www.hubblesite.org
www.geol.umd.edu/kaufman/ ppt/chapter4/sld002.htm
www.psi.edu/projects/ planets/planets.html
See Fig. 1.9
3
Formation of the Planets

• Nuclear fusion began within the mass at the
  center of the solar system forming the sun
• The inner planets were hotter and gas was driven
  away leaving the terrestrial (rocky) planets
• The outer planets were cooler and more massive so
  they collected and retained the gasses hence the
  Gas Giants

Terrestrial Planets
?
Gas Giants
www.amnh.org/rose/backgrounds.html
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Differentiation of the Planets

• The relatively uniform iron-rich proto planets
  began to separate into zones of different
  composition 4.5bya
• Heat from meteor impact, pressure and radioactive
  elements cause iron (and nickel) to melt and sink
  to the center of the terrestrial planets

See Fig 1.10
5
Further Differentiation of Earth
Deepest Mine
Deepest Well
Continental Crust (Silicic)

• Lighter elements such as Oxygen, Silicon, and
  Aluminum rose to form a thin, rigid crust
• The crust, which was originally thin and basaltic
  (iron rich silicate), further differentiated to
  form continental crust which is thicker, iron
  poor, silica rich and lighter

Oceanic Crust (Basalt)
Mid-Ocean Ridge (New Crust)
See Fig. 1.11
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Composition of Earth and Crust
 
 
?Before and ?After Differentiation
 
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Crust and MantleLithosphere and Asthenosphere

• The uppermost mantle and crust are rigid solid
  rock (Lithosphere)
• The rest of the mantle is soft but solid
  (Asthenosphere)
• The Continental Crust floats on the uppermost
  mantle
• The denser, thinner Oceanic Crust comprises the
  ocean basins

Figure 1.11, Detail of crust and Mantle
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A Large Variety of Rocks (and Sediment)Products
of an Active Planet
Crust Rigid, Thin

• Earths structure leads to intense geologic
  activity
• Inner core Solid iron
• Outer core Liquid iron, convecting (magnetic
  field)
• Mantle (Asthenosphere) plastic solid,
  iron-magnesium silicate, convecting
• Crust (Lithosphere) Rigid, thin
• O, Si, Al, Fe, Ca, Na, K, Mg

Mantle Plastic, Convecting
47, 28, 8, 5, 4, 3, 3, 2
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Lithospheric Plates
See Kehew, Figure 1.19

• The Lithosphere is broken into plates (7 maj.,
  6 or 7 min.)
• Plates that ride around on the flowing
  Asthenosphere
• Carrying the continents and causing continental
  drift

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Lithospheric Plates
Fig. 1.13 and 2.14
11
Three Types of Plate Boundaries

• Divergent
• Convergent
• Transform

See Fig. 1.14 and 1.13
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Things to Know About Plate Tectonics

• Composition and properties of Zones
• Iron core (solid liquid, convecting, magnetic
  field)
• Mantle Plastic solid, convecting, ultramafic
  (Si, O, Fe,Mg)
• Composition and Properties of the Crust
• Oceanic Crust Basalt, Thin (5-10km) (O, Si, Fe,
  Mg, Ca)
• Continental Crust Granitic, Thick (10-50km) (O,
  Si, Al, Na, K)

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Things to Know About Plate Tectonics

• Features and Geologic Phenomena
• Convergent trenches, mountain chains, granitic
  magma, granitic rocks, composite volcanoes,
• Divergent Mid ocean ridges, rift valleys,
  shallow earthquakes, basaltic magma and lava,
  basalt, lava floods (volcanoes rare)

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Things to Know About Plate Tectonics

• Features and Geologic Phenomena
• Transform Offset ocean ridges or mountain
  chains, shallow earthquakes, no magma or lava
• Hotspots Shallow earthquakes, basaltic magma and
  lava, basalt, lava floods, sometimes shield
  volcanoes

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The 3 rock types form at convergent plate
boundaries

• Igneous Rocks When rocks melt, Magma is formed,
  rises, cools and crystallizes.
• Sedimentary Rocks All rocks weather and erode to
  form sediments (e.g., gravel, sand, silt, and
  clay). When these sediments accumulate they are
  compressed and cemented (lithified)
• Metamorphic Rocks When rocks are compressed and
  heated but not melted their minerals
  re-equilibrate (metamorphose) to minerals stable
  at higher temperatures and pressures

Sedimentary Rocks
Metamorphic Rocks
Igneous Rocks
Magma
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The Rock Cycle
Geological Materials Transformation
Processes

• Geologic materials
• (blocks)
• Are transformed and transported
• By geologic processes
• (arrows)
• To form other geologic materials
• Driven by internal and external processes

Fig. 3.1
See Fig. 1.15
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Igneous and Sedimentary Rocks at Divergent
Boundaries and Passive Margins

• Igneous Rocks (basalt) are formed at divergent
  plate boundaries and Mantle Hot Spots. New
  basaltic, oceanic crust is generated at divergent
  plate boundaries.
• Sedimentary Rocks are formed along active and
  passive continental margins from sediments shed
  from continents

• Sedimentary Rocks are formed on continents where
  a basin forms and sediments accumulate to great
  thicknesses. E.g., adjacent to mountain ranges
  and within rift valleys.

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Learning Plate Tectonic Geography

• Brushing up on basic geography will help you
  learn Plate Tectonics
• Once you know your basic geography and ocean
  basin features (Mid Ocean Ridges, -Oceanic
  Trenches) you can
• Learn the 7 major plates
• Learn the types of plate boundaries
• Learn why those features are where they are