Chapter 9

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

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 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

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

Were you right?

fault: break or crack along which rocks move caused by stress

faulted rocks have two blocks: hanging wall: block of rock above fault foot wall: block of rock below fault

Types of Faults normal fault: formed when hanging wall moves down relative to the foot wall

reverse fault: formed when hanging wall moves up relative to the foot wall

strike-slip fault: rocks on either side of fault are moving past each other

fold: bend in the rock (rock deformed but doesn’t break) anticline: upward fold in the rock (forms ridges) syncline: downward fold in the rock (forms valleys)