Transcript Plates of the Lithosphere - Cal State LA

Plates of the Lithosphere
Wegener’s Hypothesis
• Pangaea
– Giant supercontinent of
the Paleozoic and
Mesozoic eras
• Continental Drift
– The breakup of Pangaea
where plates moved away
from each other
[Insert Fig. 30.1 - Pangaea]
Evidence of Continental Drift
• Fossils
– Animal and plant
fossils appeared to
have evolved in the
same geographic
region but now
scattered on separate
continents
Certain fossils appear in continuous bands across
continents that are now separated across oceans. © Earth
Observatory NASA
Dismissal of Continental Drift
• Wegener could not produce a plausible
mechanism as to how the continents drifted
South America and Africa continents separated by the Atlantic Ocean appear to fit
together like pieces of a puzzle. © Earth Observatory NASA
Emergence Plate Tectonics Theory
• Seafloor
Spreading
– New basaltic
rock forms
along midocean ridges
and old
seafloor is
destroyed at
deep ocean
trenches
Evidence of Seafloor Spreading
• Mid-ocean ridge
– Linear mountains present in all ocean basics
• Age of ocean floor rocks
– Young rocks near ridges and become progressively older
with increasing distance from the ridges
Continental Drift Re-examined
• As a rift develops in a
continental landmass, an
ocean begins to open up
• As new seafloor is
created along mid-ocean
ridges, ocean floor
diverges moving older
seafloor away
Plate Tectonics Theory
• Lithospheric Plates
– Large segments of lithosphere
• Plate Tectonics
– The formation, movement and destruction of
lithospheric plates
Location of Plate Boundaries
• Earthquakes, volcanoes and mountain ridges
mark the location of plate boundaries
Movement of Plates
Cross section illustration of the three main types of plate boundaries: Divergent, convergent
and transform plate boundaries © USGS
Divergent Plate Boundaries
• Tensional forces result in plates moving apart
Convergent Plate Boundaries
• Compressional forces result in plates colliding with
each other
• Depending on the types of crust that are colliding,
convergent boundaries produce different land features
Convergent Plate Boundaries
Convergent Plate Boundaries
Transform Boundaries
• Shear forces result in two plates sliding past each
other