Plate Tectonics

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Plate Tectonics

• Earths InteriorLayers of the Earth
• Drifting ContinentsPlate Boundaries

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1. Earths Interior

• We know about the earths interior from indirect
  evidence
• Example of indirect evidence Finding where to
  hang a picture so that it stays hung solidly
• Temperature and pressure change
• Temperature increases towards the center of the
  earth
• Pressure also increases towards the center

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• Cross-section of earths interior showing crust,
  mantle and the two parts of the core

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Three Main Layers of the Earths Interior

• The crust the layer of rock that forms the
  earths outer skin, includes rocks, mountains,
  soil and water
• The mantle 5-40 km down. Rock is of hotter
  temperatures. About 3,000 km thick
• The core two parts outer core which is molten
  meltal and inner core which is solid metal

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Earths Magnetic Field

• Currents in the liquid outer core force the solid
  inner core to spin at a slightly faster rate than
  the rest of the planet. These currents in the
  outer core create the magnetic field causing the
  earth to act like a giant bar magnet.

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2. Convection Currents and the Mantle

• In the upper most part of the Mantle is a rigid
  layer called the lithosphere. Litho means rocky
  or stone.
• Below the lithosphere is the asthenosphere, which
  means weak, but it is actually semi-molten and
  the semi-melted rock is moving in slow currents!

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Convection

• Convection is heat transfer by movement of heated
  fluid (gas or liquid).
• Heat transfer by convection is caused by
  differences of temperature and density within
  that fluid
• The heating and cooling of the fluid, changes in
  the fluids density, and the force of gravity all
  combine to set convection going in the earths
  mantle.

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These convection cells move sections of the
crust. Hot, less dense molten lava rises to the
surface creating new crustal sections. Old crust
is subducted down in the earth, melting and
recycling!
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3. Drifting Continents

• 1910 Alfred Wegener hypothesized that all the
  continents had once been joined together in a
  single landmass and have since drifted apart.
• Evidence includes mountain ranges that line up,
  fossils that were similar, mineral deposits that
  also lined up, and climate evidence and traces
• Most scientists at the time did not believe in
  this theory of drifting continents, as Wegener
  could not explain what force was actually moving
  the continents.

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4. Sea-Floor Spreading

• Mapping the Mid-Ocean Ridge the longest chain
  of mountains in the world!
• Sonar mapping(begun in 1959) revealed the
  location of these Mountains

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Evidence of Sea-Floor Spreading

• Ocean floors move like conveyor belt, carrying
  the continents along with them.
• At the mid-ocean ridge, molten material rises
  from the mantle and erupts. The molten material
  then spreads out, pushing older rock to both
  sides of the ridge.

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Evidence of Sea-Floor Spreading

• Molten material found erupting along mid-ocean
  ridge
• Iron within basaltic crust was magnetized. Strips
  on either side of the mid-ocean ridge matched up

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Subduction at Deep-Ocean Trenches

• Trenches forms where the oceanic crust is
  thrust back down into the mantle and begins
  cracking and melting

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Location of earthquakes and volcanoes
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Ring of Fire
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Plates of the Earth
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Plate BoundariesConvergent, Diverent, Transform
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Motion of Indias plate
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San Andreas Fault in California
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How islands are formed Hot spots in the crust
allow melted magma to form little cones on the
ocean floor that build higher and higher to form
islands.
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