 Alfred Wegener – developed the Continental Drift hypothesis  The continents were once joined as one single “supercontinent”  Pangea was the name given by Wegener for the connected large landmass (means “all land”)

A. Continental Drift  Similarities in the coastlines of South America and Africa raised questions about “one big land mass”

 Evidence to support the Continental Drift  The coasts of different continents look similar  Especially South America and Africa  Similar rock formations and coal deposits found on different continents

 Similar fossils on different continents  Several mountain belts end at a coastline but reappear on a landmass across the ocean  Appalachian Mountains run NE through the Eastern US  Similar mountains of the same age and same type of rocks are found in British Isles  When put together, they form a continuous chain

 Evidence of past tropical climates in the Antarctic.  Fossils of Glossopteris, a fern-like tropical plant found in colder areas  Arctic climates (glacier marks) in the tropics.

 Wegener’s Theory was heavily criticized  He could not provide evidence or the cause of the force that moved the continents to their current positions  A new theory was born – Plate Tectonics!

B. Plate Tectonics  The geological theory that states the pieces of Earth’s lithosphere are in constant slow motion  This is driven by currents in the asthenosphere  The lithosphere is divided into segments called plates which effect each other  Collide  Pull apart  Grind past each other

 These movements affect Earth’s surface  Volcanoes & Earthquakes  Mountains & Valleys  Mid-Ocean Ridges & Deep Sea Trenches

 Plate Boundaries & Faults  The edges of each piece of a plate is called a boundary  The cracks in the Earth’s crust along these boundaries are called faults

Types of Plate Boundaries  Transform Fault Boundaries  2 plates grind past each other without creating nor destroying the Earth’s crust  San Andreas Fault in California  These can create NEW PLATE boundaries  Responsible for Earthquakes

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 Divergent Plate Boundaries  When 2 plates move apart or divide  Creates Mid-Ocean Ridges  Mid-Atlantic Ridge formed by divergent boundaries  Longest chain of mountains/volcanoes in the world even though its all under water

 Seafloor spreading – new oceanic lithosphere produced  Rift valleys also formed – plate separation on land  Rio Grand and Great Rift Valley

 Convergent Plate Boundaries  When 2 plates come together  Forms deep water trenches  The canyon forms where the ocean crust plunges back  The more dense and older rock sinks – called subduction  Andes, Cascades, Sierra Nevadas

 Can form volcanoes  The subducted plate melts  The melted rock is less dense and rises to create the volcano

C. Causes of Plate Motion  Slab Pull  Old ocean crust that is more dense sinks into the asthenosphere and pulls some of the lithosphere with it  Ridge Push  Oceanic lithosphere slides down the sides of an oceanic ridge (gravity)

 Mantle Convection  Mantle is the middle layer of the Earth  It is constantly cooled and heated causing uneven heating of the Earth  It’s like the crust “floats” on the mantle

D. The Earth’s Major Plates