Continental Drift

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Continental Drift
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How many continents are there?
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Were the continents always located in the same
position?
Drift animations
http//www.classzone.com/books/earth_science/terc/
content/visualizations/es0806/es0806page01.cfm?cha
pter_no08
http//www.wwnorton.com/college/geo/egeo/flash/2_1
.swf
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A continental puzzle
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• In 1912 a German meteorologist named Alfred
  Wegener noticed that the continents fit together
  like puzzle pieces.
• He proposed that the continents were joined
  together in the past, in a large land mass called
  Pangaea.

http//www.sci.csuhayward.edu/lstrayer/geol2101/2
101_Ch19_03.pdf
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• Over time, the continents drifted apart Wegener
  named his theory Continental Drift.

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He supported his theory with four pieces of
evidence.

• 1. Puzzle like fit of continent edges

http//maps.google.com
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• 2. Matching fossils of plants and animals on once
  connected land areas.

Fossils of Glossopteris are found in Permian
rocks of South Africa, India, Australia, South
America, and Antarctica
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• 3. Rock similarities and ages

Mountains in South America and Antarctica are
believed to have formed as part of the same
mountain chain.
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• 4. Climate evidence (Glacial evidence in Africa,
  South America, Australia, and India and tropical
  plant fossils in Arctic areas)

Fossils found in Antarctic soil indicate that the
now frigid continent was once lush with trees and
ferns, and home to dinosaurs, amphibians, and
later, marsupials.
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Wegeners theory made sense, but no one wanted to
accept it until they knew HOW the continents
moved.
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• In the 1960s, a Princeton University scientist
  named Harry Hess, discovered how the continents
  drifted.

Continental Drift Whiplash
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Seafloor Spreading

• Magma in the mantel rises and pushes the plates
  apart, forming new oceanic crust.

http//education.sdsc.edu/optiputer/flash/seafloor
spread.htm
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Seafloor Spreading causes Continental Drift
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Supporting evidence of seafloor spreading

• 1. Magnetic iron particles record the time of
  the rock formation. http//www.wwnorton.com/colleg
  e/geo/egeo/flash/2_3.swf
• 2. Rocks farther away from the opening age at the
  same rate on both sides. http//www.wwnorton.com/c
  ollege/geo/egeo/flash/2_5.swf

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A map of the ocean floor provides even more
evidence http//maps.google.com/
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Iceland shows seafloor spreading above the water,
which makes it easier to study
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Plate Tectonic Theory

• Theory of Plate Tectonics -Earths crust is
  broken into plates which float and move.

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Earths crust made of many plates is similar to
the panels on the outside of a soccer ball.
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There are about 13 plates covering Earths surface
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Plate Boundaries (edges)

• When the plates move, their boundaries, or edges,
  can scrape and collide.

http//www.wwnorton.com/college/geo/egeo/flash/2_6
.swf
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Convergent Boundary

• Plates move toward each other

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Convergent Boundary

• When two continental plates move into each other,
  the plates combine and form mountains. (India
  into Asia)

http//www.classzone.com/books/earth_science/terc/
content/visualizations/es1105/es1105page01.cfm?cha
pter_novisualization
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Convergent Boundary

• When an oceanic plate runs into a continental
  plate, the heavier oceanic plate subducts (sinks)
  back into the mantle.
• Volcanic mountains are created along this edge.

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Oceanic plate into continental

• Example Pacific plate (oceanic) subducts (sinks)
  under Japan (continental). http//maps.google.com/
  

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Divergent Boundary

• Plates move apart

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When both diverging plates are both oceanic, it
is called seafloor spreading (Mid-Atlantic
Ridge)
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When both diverging plates are continental it is
called rift valley formation (Africa)
http//highered.mcgraw-hill.com/olcweb/cgi/pluginp
op.cgi?itswf640480/sites/dl/free/0072402466
/30425/19_21.swfFig.2019.2120-20Evolution20o
f20a20Divergent20Plate20Boundary
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Transform Boundary

• Plates slide past each other

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San Andreas Fault
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San Andreas Fault, CA

• Each time the plates slide past each other, an
  earthquake occurs

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Find the three boundaries
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Asthenosphere

• A plastic-like layer found below the lithosphere.
• The rigid oceanic and continental plates of the
  lithosphere sit on top

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The Asthenosphere is heated by the hot Outer Core
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Convection Current
crust
mantle
core

• Hot material rises, cooler material sinks,
  creating a current, called a Convection Current

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When the asthenosphere moves, it carries the
lithospheric plates (divergent, convergent, and
transform motions)Convection currents cause
plate motion
http//www.absorblearning.com/media/attachment.act
ion?quick12patt2775
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Every time these plates move we get earthquakes,
volcanic eruptions, and possibly tsunamis