Plates of the Lithosphere

• Pangaea– Giant supercontinent of

the Paleozoic and Mesozoic eras

• Continental Drift– The breakup of Pangaea

where plates moved away from each other

Wegener’s Hypothesis

[Insert Fig. 30.1 - Pangaea]

• Fossils– Animal and plant

fossils appeared to have evolved in the same geographic region but now scattered on separate continents

Evidence of Continental Drift

Certain fossils appear in continuous bands across continents that are now separated across oceans. © Earth Observatory NASA

• Wegener could not produce a plausible mechanism as to how the continents drifted

Dismissal of Continental Drift

South America and Africa continents separated by the Atlantic Ocean appear to fit together like pieces of a puzzle. © Earth Observatory NASA

• Seafloor Spreading– New basaltic

rock forms along mid-ocean ridges and old seafloor is destroyed at deep ocean trenches

Emergence Plate Tectonics Theory

• 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

Evidence of Seafloor Spreading

• 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

Continental Drift Re-examined

• Lithospheric Plates– Large segments of lithosphere

• Plate Tectonics– The formation, movement and destruction of lithospheric plates

Plate Tectonics Theory

• Earthquakes, volcanoes and mountain ridges mark the location of plate boundaries

Location of Plate Boundaries

Cross section illustration of the three main types of plate boundaries: Divergent, convergent and transform plate boundaries © USGS

Movement of Plates

• Tensional forces result in plates moving apart

Divergent 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

Convergent Plate Boundaries

• Shear forces result in two plates sliding past each other

Transform Boundaries