Transcript Origin of Continents oldest rocks ≈ 4-billion-year-old

Continental Crust
Thicker
Less dense
Older (up to 4 billion)
vs
Oceanic Crust
Thinner
More dense
Younger (< 220
Million
Figure 13-7
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Continental Crust
Thicker
Less dense
Older (up to 4 billion)
vs
Oceanic Crust
Thinner
More dense
Younger (< 220
Million)
Figure 13-7
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2
Continental Crust
Thicker
Less dense
Older (up to 4 billion)
vs
Oceanic Crust
Thinner
More dense
Younger (< 220 Million)
Figure 13-7
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Nature of the Ocean Floor: Topography
Convergent Boundaries = Trenches
Nature of the Ocean Floor: Topography
Mid Ocean Ridges = Divergent Boundaries
Continents grow by collisions
Forming mountains at
continent-continent convergent boundaries
Figure 13-7
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Continents grow by collisions
Forming mountains at
continent-continent convergent boundaries
Ex. India & Asia
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The continents move through time. 225 million
years ago they combines into one
supercontinert called “Pangea”
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Cascadia subduction zone
http://en.wikipedia.org/wiki/Image:Subduction.jpg
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Cascadia subduction zone
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Earth Quakes in the Cascadia subduction zone
Note zone with few E.Q.s = locked
= potential for very large quake (9.0+)
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http://www.nps.gov/archive/olym/geology/accretion.htm