Chapter 6: Plate Tectonics

Divergent Boundary

Divergent boundary- where 2 plates are moving apart Typically located along mid-ocean ridges although they can also be found on land New crust forms because magma pushes up and hardens in the rift zone between separating places (seafloor spreading) Earthquakes occur as the plates spread apart

Mantle

Middle layer Thickest layer Top portion called Asthenosphere Density increase with depth due to increase in pressure Hot softened rock Contains Iron (Fe) and Magnesium (Mg)

Motion of Lithospheric Plates

Plates float on the upper part of the Mantle Convection currents can cause the asthenosphere to flow, slowly carrying with it the plates of the lithosphere This movement of plates changes the sizes, shapes and positions of Earth's continents

Crust

Relative Position Density Composition Outermost layer Oceanic crust is thinner than continental crust Crust and top of mantle are called Lithosphere Least dense layer Ocean crust (Basalt) is more dense than continental crust (Granite) Solid rock made of mostly Silicon (S) and Oxygen (O) Oceanic crust- Basalt Continental crust- Granite

The Claims That Plate Tectonics Account For

The distribution of fossils on different continents The occurrence of earthquakes Continental and ocean floor features (mountains, volcanoes, faults & trenches)The continents fit together almost like puzzle pieces forming Pangaea (1 super continent) Fossils on different continents are similar to fossils on continents that were once connected. When the continents split, different life forms developed. Most continental and ocean floor features are the result of geological activity and earthquakes along plate boundaries. The exact patterns depend on whether the plates are converging (being pushed together) to create mountains or deep ocean trenches, diverging (being pulled apart) to form new ocean floor at mid-ocean ridges or sliding past each other along surface faults. Most distributions of rocks within Earth's crust, including minerals, fossils fuels (coal, oil & natural gas) and energy resources, are a direct result of the history of plate motions and collisions and the corresponding changes in the configurations of the continents and ocean basins. This history is still being written. Continents are continually being shaped and reshaped by competing constructive and destructive geological processes. Ex. North America has gradually grown in size over the past 4 billion years through a complex set of interactions with other continents, including the addition of many new crustal segments.

The Theory of Plate Tectonics

The theory of plate tectonics explains the past and current movements of rocks at Earth's surface and provides a framework for understanding its geological history. Plate movements are responsible for most continental and ocean floor features and for the distribution of most rocks and minerals within Earth's crust. Evidence that supports the theory of plate tectonics includes distribution of rock formation and fossils, shapes of existing continents, ocean floor features and seismic and volcanic activity. This evidence shows how Earth's plates have moved great distances, collided and spread apart throughout Earth's history.

Convergent Boundary

where 2 plates come together and collide Activity depends upon the type of crust that meet More dense oceanic plate slides under less dense continental plat or another oceanic plate forming a trench at the subduction zone where crust is melted and recycled. Along these trenches, island arcs and volcanic arcs can be created. 2 continental plates converge, both plates buckle and push up into mountain ranges or volcanoes Earthquakes occur as the plates collide

Transform Boundary

where 2 plates slide past each other Crust is neither created or destroyed Earthquakes occur frequently as plates slide past each other

Core

Inner layer Two parts- outer core and inner core Heaviest material Most dense layer Mostly Iron (Fe) and Nickel (N) Outer core- slow flowing liquid Inner core- a spinning solid

Changes in Landform areas over Geologic Time

Plates move at very slow rates, averaging about 1-10 centimeters per year At one time in geologic history the continents were joined together in one large landmass that was called Pangea. As the plates continued to move and split apart, oceans were formed, landmasses collided and split apart until the Earth's landmasses came to be in the positions they are now Evidence of these landmass collisions and splits includes identical fossil formations found on separate continents, landform shapes and features, identical rock formations found on separate continents and paleoclimate evidence (ex. Evidence of warmer climates found in Antarctic fossils). Landmass changes can occur at hot spots within Lithospheric plates. Volcanic activity occurs as magma rises and leaks through the crust. Earth's plates will continue to move. Landforms of Earth can be created or changed by volcanic eruption and mountain building forces.