All of the phenomena that we will discuss over the next month are all a result of plate tectonics. • Plate Tectonics is the idea that the Earth is broken up into a number of plates. These plates have been, and are currently moving over the face of the Earth. Some are pulling away, some are pushing together, and others are sliding by one another. • The majority of volcanic eruptions and earthquakes are the direct result of this plate motion..
Alfred Wegener…. (The Father of Continental Drift…) • Was the first to come up with the idea that the continents were moving… • His theory is known as… Continental Drift… - Earths continents are in motion……
Pangea…. • Alfred Wegner also believed that at one time in the past, all of the continents were once fit together. • He called this “Super Continent”…….. Pangea.
Wegner’s Clues or Evidence….. • Shape of the continents – • They seem to fit together as one big puzzle….
Clues or Evidence continued… • Fossil evidence
Clues or Evidence continued… • Climate (Glacial Deposits)..
Clues or Evidence continued… • Rocks - similar mountain ranges found on different continents separated by oceans…
Was Wegner’s idea accepted ??? • NOOOOOO ! ! ! ! • Why ? ? • He could not explain what is making them move ! !
Seafloor Spreading • Wegener believed only the continents were moving around the globe while plowing through the ocean floor • How could they move through something that was solid? • Technology allowed scientists to map the sea floor and they found that the sea was not completely flat • There were deep canyons, huge mountains, etc. • How did they form?
Seafloor Spreading • Harry Hess proposed that sea floor was being formed at ridges and by intruding magma • This pushes older ocean floor further and further apart • Trenches were the sites where ocean crust was destroyed
What is Moving the Plates? Convection Currents
Evidence for Sea Floor Spreading • Age of the rocks • As you go away from the ridge the rocks get progressively older
Evidence for Seafloor Spreading • The pattern of normal and reverse magnetism • Mirror images on either side of the ridge
Plate Movement • The Earth is divided into many layers • Crust, Mantle, Core • However there are other layers • Lithosphere – solid, crust and upper mantle • Asthenosphere – partially molten and will flow, part of the mantle
Convection • Heat from the core of the earth rises, cools and sinks • This puts the asthenosphere in motion • The overlying plates are then put into motion as well
Types of Plate Boundaries • Convergent – Plates moving towards one another • Divergent – Plates moving away from one another • Transform – Plates move side by side
Divergent Plate Boundaries • Forms a rift valley where the plates are splitting apart • Examples: • Mid-Atlantic Ridge • East African Rift Valley
Convergent Plate Boundaries • Can form mountain ranges/volcanoes • Types • Continent-Continent collisions • Ocean-Continent collisions • Ocean-Ocean collisions
Continent-Continent collisions • Rocks have the same densities on either plate so upon collision the rocks go up. • Example: Himalaya Mountain Range • Indo-Australian Plate and the Eurasian Plate
Continent-Ocean Collisions • The 2 plates of different densities so the plate with higher density goes underneath the plate with the lower density • This is called subduction • The oceanic plate goes deeper and deeper until it melts and eventually gets erupted from volcanoes • A trench is formed where the subduction occurs
Examples of continent-ocean collisions • Nazca plate – South American plate • Results in the Andes Mountains
Juan de Fuca plate and the North American plate • Creates the Cascade Range
Ocean-Ocean collisions • Subduction still occurs because the older of the ocean plates will have a higher density • Creates volcanic islands • Example: Pacific Plate and the Eurasian Plate • Creates the Japanese Volcanic Island Arc
Transform Boundaries • Plates are sliding past • Can create mountains • Example: Pacific plate and the North American plate • The boundary between these two is known as the San Andreas Fault