Plate Tectonics

1
Plate Tectonics

• Some of the first people to consider moving
  landmasses were early mapmakers.
• These mapmakers noticed the similar and seemingly
  matching coastlines on different continents.

2
Plate Tectonics

• Late 1800s Eduard Suess, Austrian geologist
  hypothesized that some of the present continents
  had once been joined in a single landmass he
  called Gondwanaland.
• It wasnt until the early 1900s that the idea of
  moving continents gained popularity among
  scientists.

3
Plate Tectonics

• 1912 Alfred Wegener proposed continental drift
  to scientific community
• Continental drift The present continents had
  drifted away from what was once a single large
  landmass Pangaea
• Pangaea began to break apart about 200 million
  years ago

4
Plate Tectonics

• Wegener based his hypothesis on several different
  types of data
• Similar coastlines on different continents
• Similar rock types on different continents
• Fossils of land-based animals on different
  continents
• Finding fossils of warm-climate animals/plants in
  cold climates

5
Plate Tectonics

• Study of the ocean floor led scientists to
  possible causes for continental drift
• Many deep-sea trenches and ocean ridges were
  discovered.
• Scientists found that the age of rocks in the
  ocean floor increase with the distance from an
  ocean ridge.

6
Plate Tectonics

• Many rocks on the ocean floor were found to be
  much younger than continental rocks.
• The thickness of ocean-floor sediment increases
  with distance from an ocean ridge.
• Deep sea trenches contain some of the oldest
  rocks on the ocean floor.

7
Plate Tectonics

• The theory of seafloor spreading states that new
  ocean crust is formed at ocean ridges and
  destroyed at deep-sea trenches.
• Magma is forced up as the seafloor spreads. This
  magma cools and becomes new seafloor

8
Plate Tectonics

• Theory of Plate Tectonics states that the
  Earths crust and rigid upper mantle are broken
  into enormous slabs called plates.
• Plate boundaries places that tectonic plates
  interact. They can converge, diverge, or slide
  horizontally

9
Plate Tectonics

• Divergent boundaries places where two tectonic
  plates are moving apart
• The actual boundary is located in a rift.
• These boundaries are known for high heat flow,
  volcanism, and seismic activity.
• The Mid-Atlantic Ridge is a divergent plate
  boundary. The plates are moving apart at a rate
  of about 2-3 cm/yr.

10
Plate Tectonics

• Convergent boundaries places where two tectonic
  plates are moving toward each other.
• There are three types of convergent boundaries
• Oceanic-oceanic creates a trench and a range of
  mountains under the ocean
• Oceanic-continental creates a trench off the
  coast and a volcanic mountain range on the
  continent
• Continental-continental creates mountain ranges

11
Plate Tectonics

• Subduction when one plate slides under another
  at a convergent boundary
• One plate is made of denser materials than the
  other and is thus subducted.
• The subducted plate slides into the mantle and
  melts.

12
Plate tectonics

• Some magma is forced up and creates volcanic
  activity on the ocean floor or above the ocean
  surface on islands
• Oceanic-oceanic Aleutian islands
• Oceanic-continental Andes mountains
• There is no subduction at a continental-continenta
  l convergent boundary
• example Himalayas

13
Plate Tectonics

• Transform boundaries place where two plates
  slide horizontally past each other.
• Crust is simply deformed and/or fractured at
  transform boundaries.
• Characterized by long faults and shallow
  earthquakes
• Example San Andreas Fault in California

14
Plate Tectonics

• Causes for plate motion
• Mantle convection
• Horizontal flow in the convection currents in the
  mantle cause the plates to float horizontally
• Ridge push
• New magma rising out of an ocean ridge and
  cooling helps to push the plate away from a
  diverging boundary
• Slab pull
• The sinking plate at a subduction zone pulls
  the plate along at a converging boundary

15
Plate Tectonics

• Unanswered questions
• How did continental drift start?
• Is mantle convection a permanent feature?
• What causes a mantle convection current to start
  and stop?
• Do these convection currents take place
  throughout the whole inner Earth?