The Earth by urschoice


									The Earth

• Insides
• Plate Tectonics
• How the Philippines
  Came to Be
The Earth’s Surface

• Has the Earth’s surface always been this way?
• Is it just a coincidence that Africa and the
  Americas seem to have split from each other?
Continental Drift Theory
• First developed by Alfred Wegener (1912)
• Shapes of continents suggest they were once
• Rocks and fossils on continents on opposite sides
  of oceans are identical and of same age
• Parts of Africa and India were once buried in ice
  sheets; North America and Northern Europe hold
  fossils of tropical organisms
• More evidence in 1960’s:
  – Polar wandering, reversal of magnetic poles
  – Sea floor spreading
Evidence for Continental Drift
                             Similar fossils occur in
                             separate continents

     Geologic histories of
      regions in separate
continents best explained
      by their being once
   adjacent to each other
• Theory was initially
  dismissed due to the
  lack of a mechanism
  to cause massive
  continents to move
 Plate Tectonics: Main premises
• Earth’s crust made up of plates (~20)
   – Two kinds: oceanic plates (denser and thinner),
     continental plates
• Plates move as if on a conveyor belt (the mantle),
   – Speed: 10 cm/yr (10,000 kms in 100 million years)
• Mantle flows like a viscous liquid
   – Energy comes from radioactive decay
   – Unequal heating leads to convection currents
   – Plates float on and move with flowing mantle
• Many geologic processes take place near plate
   – Volcanoes, sea-floor spreading, earthquakes, mountain
Mechanism for Continental Drift:
Convection Currents in the Mantle
                          • Parts of the Mantle
                            are hotter than
                          • Hot spots expand
                             decrease density
                             become buoyant
                             rise like a
              H OT          balloon
                          • Adjacent areas
                            move in to fill

                            spaces left behind
                            by rising fluid
                          • Cool spots sink,
                            creating a loop
The Plates

    Geologically active areas are at plate boundaries
        Convergent: Subduction
        zones; destroys crustal

                   Types of Plate
Divergent: Ocean
ridges; creates
new crustal            Conservative: Near faults;
material                 translational, no loss nor
                       creation of crustal material
                            • Form along a line (arc) near
                              subduction zones
                            • Water in subducted oceanic
                              plate helps form magma
                            • Associated with trenches,
                              deepest parts of the ocean
• May also form over hot spots in the mantle, or where two
  oceanic plates converge
Sea Floor Spreading

• Occur at mid-oceanic ridges where mantle is moving apart, creating
  openings for magma to be released and form new crust
• Rocks are older the farther away from ridge

• Form near plate edges, or where plates are weakest
  (faults) or subject to stresses
• Occur when rocks suddenly give way to pressure
Mountain Ranges
• Form where two continental plates
  push against each other
 The Philippines

• Country lies on a narrow oceanic
  microplate between Eurasian Plate
  and Philippine Plate                  • Part of Pacific Rim of Fire
• Philippine Plate is oceanic, moving   • Near subduction zones, trenches
  northward into Eurasian plate           and faults; highly active
The Philippines
• Plate tectonics explain many
  of its features
  • Rich in limestone due to oceanic
  • Highly volcanic; most of its
    mountains and lakes are extinct
  • Rich in mineral resources
  • Earthquake-prone
  • Too young to contain dinosaur
  • Rich in diversity – biological and
• In a few tens of millions of
  years, islands will disappear

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