Phys 102: Natural Systems

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Phys 102 Natural Systems
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Introduction
Lecture 7
Phys 102 Natural Systems
Introduction

• Weve looked at thermodynamics and systems theory
  in general.
• Weve applied the 1st and 2nd laws to the
  dynamics of the hydrosphere, atmosphere, phase
  changes of water and temperature stability on
  earth.
• Weve applied systems theory (briefly) to
  describe the homeostasis of Gaia

Now we will apply the ideas to the evolution of
the lithosphere and then move onto biotic systems.
Vincent Conrad
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Plate Tectonics
Lecture 7
Phys 102 Natural Systems
Plate Tectonics

• Alfred Wegener, the German meteorologist around
  1920 layed the foundations of the theory.
• Alfred presented the first detailed accounts of
  how today's continents were once a large
  supercontinent.
• The mechanism moving the plates is probably
  related to the transfer of heat energy or
  convection within the earth's mantle.
• Plate tectonics processes and continental drift
  did not attract wide interest until the late
  1950s, when scientists found paleomagnetic
  evidence for the theory.

Vincent Conrad
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Paleomagnetism
Lecture 7
Phys 102 Natural Systems
Paleomagnetism

• Earth has a magnetic field
• Dipole running geographic N-S (but other way)
• Structures forming magnetic rocks align with this
  field.
• Field flips occasionally (last time was 780
  Kyears ago).
• Hence noting the orientation of magnetic fields
  in rocks provides evidence for which parts of the
  earths surface were once connected.

The study of the evolution of the planet in this
way is paleomagnetism.
Vincent Conrad
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Continental Drift
Lecture 7
Phys 102 Natural Systems
Continental Drift

• Looking at a map of the world, the continents
  sort of look like jigsaw pieces.
• This lead to the idea that all the continents
  were once connected, and have drifted apart.

Paleomagnetic, biological, and ice movement
evidence supports the hypothesis, establishing
the theory of continental drift.
This evidence suggests that about 200 million
years ago the continents we call Europe, Asia,
Nth America, South America were combined as one
continent called Pangaea.
Continental drift developed into the idea of
plate tectonics.
Vincent Conrad
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Plate Tectonics
Lecture 7
Phys 102 Natural Systems
World Plates
http//www.gly.fsu.edu/salters/GLY1000/Chapter5/5
Plate_Tectonics_index.html
Vincent Conrad
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Plate Structure
Lecture 7
Phys 102 Natural Systems
Plate Structure

• The lithosphere, is divided into about 7 major
  plates and perhaps as many as 12 smaller plates.

• Plates are about 100km think and make up
• the lithosphere.
• The heat in the mantle of earth causes it to flow
  slowly like heated plastic.
• The region where this starts is called the
  asthenosphere. It may start at a depth of as
  little as 100km.

• The plates move constantly, supported by the
  slowly flowing asthenosphere. (Like large pieces
  of ice floating on a lake)
• Typical speed of plates is about 3cm/year (about
  that rate of fingernail growth).
• The theory that explains how plates move and the
  processes at their boundaries is called plate
  tectonics.

Vincent Conrad
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Types of plate boundaries
Lecture 7
Phys 102 Natural Systems
Plate Tectonics
Convergent eg Mid ocean ridges Divergent eg
volcanic arcs Strike - Slip or Transform eg San
Andreas Fault through California
Vincent Conrad
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Convergent Plates
Lecture 7
Phys 102 Natural Systems
Convergent Plates

• Plates push together, forcing one over the other.
• This creates mountains and trenches.
• These are areas of explosive volcanism.

Vincent Conrad
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Divergent Plates
Lecture 7
Phys 102 Natural Systems
Divergent Plates

• magma (at 650 - 1200 C) pushes up through thin
  parts of the lithosphere.
• This causes plates to spread apart.
• Causes seabed spreading, (further evidence for
  plate tectonics theory).

Vincent Conrad
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Strike - Slip Plates
Lecture 7
Phys 102 Natural Systems
Strike - Slip Plates

• plates slide past each other.
• causes earth quakes (San Andreas Fault)

Vincent Conrad
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World Quakes
Lecture 7
Phys 102 Natural Systems
Plate Tectonics
Distribution of earthquakes is referred to as
seismicity. Most earthquakes occur along
relatively narrow belts that coincide with plate
boundaries.
Vincent Conrad
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Plate Mechanics
Lecture 7
Phys 102 Natural Systems
Plate Mechanics

• The evolution of the lithosphere is driven by
  thermodynamic processes in the mantle and core.
• In connection to the 1st law, where did all this
  energy come from?
• In connection to the second law, what will
  eventually happen to the earth?

Vincent Conrad
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End of Abiotic Section
Lecture 7
Phys 102 Natural Systems
End of Abiotic sections Now will move on to look
at biotic natural systems, and their interactions
with the biotic and abiotic environments.
Vincent Conrad
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Phys 102 Natural Systems