Earths surface consists of a number of rigid

Earth’s surface consists of a number of rigid, but moving pieces called plates Theory of Plate Tectonics: Theory that helps explain the formation and movements of these plates

Continental Drift The movement of the Earth’s continents relative to each other. • Alfred Wegener developed this hypothesis in 1912. • In the 1960 s, theory of plate tectonics allowed this idea to become more widely accepted.

Evidence of Continental Drift • • • Fossil Climatic Geological Paleomagnetic Seafloor Spreading

Fossil

Identical fossil remains of Mesosaurus, a small, extinct land reptile that lived 270 million years ago, has been found in both eastern South America and western Africa. These reptiles could not have swum across the Atlantic Ocean.

Climatic Ancient Glaciers grooves (shown by arrows) in present day structures)

Gondwana Reconstruction of Southern hemisphere super continent. Notice how ring of glaciers match the patterns of a polar ice

Geological

• Paleomagnetic

Lithosphere • This outer shell of the Earth • Made of crust and mantle • Rigid but broken into plates that move with respect to one another

Types of Earth’s Crust • Oceanic Crust – Made up of material on the ocean floor • Continental Crust – Made up of continental landmasses.

Asthenosphere • Layer within mantle that lithospheric plates rest on

Where convection currents are rising… • New material moves to Earth’s surface • Pushes older material aside • Lithospheric plates move apart

Where cooler, denser currents are sinking • Lithospheric plates are pulled together!

Plate Boundaries • Place where one plate is moving relative to another plate • Belts where earthquakes and volcanoes are located – stress builds up along boundary

• When stress is too great – fractures form and earthquakes occur • Boundaries are also area of high heat flow, magma moves upward to surface and forms a volcano

Kinds of Plate Boundaries…

Divergent boundaries • Places where two lithospheric plates are moving apart (spreading centers) • Contain mid-ocean ridges which have deep valleys along entire length called rift valleys • As plates move apart, molten rock rises and fills space between plates – cools and hardens

Transform Fault Boundaries • Lithospheric plates are sliding past one another • Transform fault – break or crack in the Earth’s crust along which movements have occurred

Example: San Andreas Fault

Converging Boundaries • Places where two plates come together • There are 3 types….

SUBDUCTION Zone • When an ocean plate and continental plate collide • Ocean plate slides under continental plate • Forms deep-ocean trench

CONT. to CONT. Convergence • Two continental plates collide • Become crumpled and uplifted • Form mountain ranges

OCEANIC TO OCEANIC Crust Convergence • One plate is subducted, forms trench • Subducted plate melts • Molten rock rises to surface along trench • Forms island chain called an ISLAND ARC

Let’s go to this website and review! CLICK HERE>>> http: //www. pbs. org/wgbh/aso/tryit/tectonics/# Click on Plate Tectonics Activity (with a yellow arrow) when you get there!

Here it is – all in one big picture… Can you pick out the types of Plate Boundaries?

Were you right?