Transcript Periodization in Earth History

Plate Tectonics
and Earth’s Interior
Pangea
Distribution of Late Paleozoic
Fossils
Conventional Wisdom:
Animals Migrated Across Land Bridges
Late Paleozoic Glaciation
Distribution of Ancient Mountain
Belts
Patterns Fit,
But Is It Possible?

Tremendous amount of energy needed to move continents
around the globe

Wegener proposed that centrifugal force on the spinning
Earth pushed continents from the south pole to the equator
• Modeling/simulation indicated that this would be insufficient

Wegener proposed that the moving continents plowed
through the oceans like an icebreaker
• Experiments indicated that oceanic rock is stronger than
continental rock, and so oceans would have cut through the
continents
Continental Drift was a Model without a Mechanism!
Bathymetry of the Ocean Floor
Volcanoes of the World
Volcanoes Correlate Globally with
Deep Earthquakes
Benioff Zone of Seismicity
Plate Tectonic Model
Tectonic Plates
Seismic Waves
Seismic Wave Velocities
Seismic Wave Paths
S-Waves
P-Waves
Layers Within Earth
Convection Cells and Plate
Movements
Plate Tectonic Model
Differentiation: Basalt

Partial melting of
peridotite will form
basaltic magma
• Basaltic magmas
are formed from
melting mantle due
to upwelling heat
Differentiation: Andesite

Partial melting of
basalt will form an
andesitic or granitic
magma
• Andesitic magmas are
formed from melting
oceanic crust
• Subducting plate
releases water (a flux)
into mantle
• Magma pools under
crust and partially melts
the oceanic crust
Differentiation: Granite

Partial melting of
andesite will form
granitic magma
• Granitic magmas are
formed from melting of
continental crust
• Subducting plate
releases water (a flux)
into mantle
• Magma pools under
crust and partially melts
the continental crust
Sources of Heat for Metamorphism


Heat from Earth’s interior
Geothermal gradient is the
increase in temperature
with depth
• Typical continental
geothermal gradient is 2530°C/km
• Volcanically active areas have
geothermal gradients of 3050°C/km
• Oceanic trenches have
geothermal gradients as low
as
5-10°C/km