Download Continental Crust

Plate Tectonics
Continental Drift
Continental drift
 Alfred
Wegener
(1921)
–Puzzle-like fit
of continents
Edward
Bullard
(1960) fit
continents at
continental
slope
Fig. 3-39b
Fig. 3-39c
–Matching
rock
structures
and ages
across
different
continents
–Extensions
of mountain
belts from
one
continent to
the other
 Glaciated
deposits
rocks and glacial
–Direction of glacial movement
–Glacial ice in what is now temperate
regions
 Other
climate evidence
–Different climates, different latitudes
 Distribution
of fossils
–Land fossils in separate continents
without “land bridges”
Objections to Wegener’s idea
 Continents
cannot “plow”
through ocean basin rocks
 Proposed energy source not
likely
–Not gravity and tides
Earth’s Interior
From nasa.gov
Fig. 3-18
Lithosphere
Oceanic crust
Basalt
Avg thickness 8 km
Continental crust
Granite
Avg thickness 35 km
Floating Plates?
Less Dense
Dense
Continental
Oceanic
Crust
Crust
(thicker)
Liquid
Mantle
Continental
crust floats
higher than
the more
dense,
thinner
oceanic
crust
Seafloor Spreading
Convection – The Driving Force