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 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

Shear forces result in two plates sliding past each other Transform Boundaries