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Plate Tectonics
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Continental
Drift theory Alfred Wegener
(1912)
Continental
Drift theory Alfred Wegener
(1912)
- He postulated that all landmasses were
originally united into a supercontinent named
Pangaea.
- Pangaea consisted of a northern landmass
called Laurasia and a southern landmass
called Gondwana.
- As Pangaea broke up, the various continents
moved to their present-day locations.
What is the Evidence for Continental Drift?
• Evidence 1: Fossil Evidence
– Some of the most compelling
evidence comes from fossils
like the Glossopteris fern.
– One of the strongest
examples is the Mesosaurus,
a fresh water reptile.
What is the Evidence for Continental Drift?
• Evidence 2.Similarity of Rock
Sequences and Mountain Ranges
– Marine, nonmarine, and
glacial rock sequences
of old age (Jurassic) are
nearly identical on all the
Gondwana continents
Fig. 2.4, p. 32
What is the Evidence for Continental Drift?
• Evidence 3. Glacial Evidence
– Glacial tills and striations on the bedrock beneath
the till provide evidence of glaciation at the same
time on all the Gondwana continents, with South
Africa located at the South Pole.
Earth’s Magnetic Field
• Paleomagnetism is the remnant magnetism in ancient
rocks recording the direction and intensity of Earth’s
magnetic field at the time of the rock’s formation.
Fig. 2.8, p. 35
Earth’s Magnetic Field
– Evidence 4 Paleomagnetic studies during the
1950's revived interest in continental drift
– The continents had moved
over time. If the continents
were moved into different
positions relative to each
other, the separate poles
could be resolved into one.
Fig. 2.9, p. 36
Earth’s Compositional Layers
Atmosphere & Hydrosphere
Crust
Mantle
Core
Lithosphere & Asthenosphere
Earth’s Tectonic Plates
What moves the plates?
Convection cells The Three Types of Plate Boundaries
• Types of Plate Boundaries
– Divergent
– Convergent
– Transform
http://www.iris.edu/hq/programs/education_and_outreach/animations/11
• B1. Divergent Boundaries – Form when plates
move away from one another.
• New oceanic lithosphere is forms
at the opening rift.
Red means younger!
• B2. Convergent Boundaries. Places where two plates collide
• B3. Transform Boundaries
– These are boundaries along which plates
slide laterally past each other along
transform faults
Fig.4.22a
Formation of Volcanic Chain
ation of Island Chains
V1
lithosphere
melting at base
of crust
V1
V1
Hot (not molten)
rising plume
Fig.4.22b
Example: The Hawaiian Chain
Fixed
hot spot
Basic Premise of Plate Tectonics
• Earth’s crust is divided into plates
• Plates move relative to one another (at 1-15 cm/yr)
• Deformation is concentrated at plate boundaries
• There are 3 types of tectonic boundaries
Consequences:
• Plate tectonics constantly change Earth’s surface
• Earthquakes occur mostly at plate boundaries
• Volcanoes occur mostly at plate boundaries