Bellringer Make your voc foldable Homework: Illistrations Essential book page 68-76

http://www.learner.org/interactives/dynamicearth/index.html

Bellringer Match your voc words Homework: Finish handout

8-3.6 Explain how the theory of plate tectonics accounts for the motion of the lithospheric plates, the geologic activities at the plate boundaries, and the changes in landform areas over geologic time.

It is essential for students to know that the theory of plate tectonics explains why and how large sections of Earth’s crust, called lithospheric plates, move. A hypothesis of continental drift was developed before the present theory of plate tectonics. It was based on continent shape, fossil evidence, rock, and climate clues. This hypothesis later led to the theory of plate tectonics when evidence was found as to why the plates could move. Plate tectonics explains how many Earth features form.

Motion of the 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 and oceans.

Geologic Activities at Plate Boundaries Divergent boundary—where two plates are moving apart • most located along mid-ocean ridge (sea-floor spreading); • new crust forms because magma pushes up and hardens between separating plates.

Convergent boundary—where two plates come together and collide • activity depends upon the types of crust that meet; • more dense oceanic plate slides under less dense continental plate or another oceanic plate – subduction zone, some crust is destroyed; • two continental plates converge, both plates buckle and push up into mountain ranges;

Transform boundary—where two plates slide past each other • crust is neither created nor destroyed; • earthquakes occur frequently along this type of boundary.

Changes in Landform areas over Geologic Time • Plates move at very slow rates – from about one to ten centimeters per year; • At one time in geologic history the continents were joined together in one large landmass that was called Pangaea. • 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 comes from fossils, landform shape, features, and rock structures, and climate change; • Landmass changes can occur at hot spots within lithospheric plates; • Earth’s landmasses will continue to move and change during the geologic time of the future.

Bellringer Make foldable of new voc words in your isn Homework: make sure essentials book is up to date p 1-28,68-76, 130-144 Draw illistrations

quiz Convergent Oceanic to oceanic Subduction Zone volcano Cont to cont Fold and thrust Cont to ocea Nic TRENCH Divergent RIFTING causes SEAFLOOR SPREADING Transform earthquakes

8.3-6 Explain how the theory of plate tectonics accounts for the motion of the lithospheric plates, the geologic activities at the plate boundaries, and the changes in landform areas over geologic time.

Theory of Plate Tectonics Plate Boundaries Causes of Plate Tectonics

Plate Tectonics

What is Plate Tectonics The Earth’s crust and upper mantle are broken into sections called plates Plates move around on top of the mantle like rafts

Plates Plates move at very slow rates – from about one to ten centimeters per year

Pangaea At one time in geologic history the continents were joined together in one large landmass that was called Pangaea

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;

Motion of the Lithospheric Plates

What is the Lithosphere? The crust and part of the upper mantle = lithosphere 100 km thick Less dense than the material below it so it “floats”

Motion of the Lithospheric Plates Plates float on the lower part of the mantle. This movement of plates changes the sizes, shapes, and positions of Earth’s continents and oceans.

What is the Asthenoshere? The plastic layer below the lithosphere = asthenosphere The plates of the lithosphere float on the asthenosphere

2 Types of Plates Ocean plates - plates below the oceans Continental plates - plates below the continents

Plate Boundaries

Divergent boundary Where two plates are moving apart; most located along mid-ocean ridge (sea-floor spreading); new crust forms because magma pushes up and hardens between separating plates.

Divergent Boundaries Boundary between two plates that are moving apart or rifting   RIFTING causes SEAFLOOR SPREADING

Features of Divergent Boundaries Mid-ocean ridges rift valleys fissure volcanoes

Convergent boundary Where two plates come together and collide; activity depends upon the types of crust that meet; more dense oceanic plate slides under less dense continental plate or another oceanic plate – subduction zone, some crust is destroyed; two continental plates converge, both plates buckle and push up into mountain ranges;

Convergent Boundaries Boundaries between two plates that are colliding   There are 3 types…

Type 1 Ocean plate colliding with a less dense continental plate Subduction Zone: where the less dense plate slides under the more dense plate VOLCANOES occur at subduction zones

Andes Mountains, South America

Type 2 Ocean plate colliding with another ocean plate The less dense plate slides under the more dense plate creating a subduction zone called a TRENCH

Aleutian Islands, Alaska

Type 3 A continental plate colliding with another continental plate Have Collision Zones: a place where folded and thrust faulted mountains form.

Transform boundary Where two plates slide past each other; crust is neither created nor destroyed; earthquakes occur frequently along this type of boundary.

Transform Fault Boundaries Boundary between two plates that are sliding past each other EARTHQUAKES along faults

San Andreas Fault, CA

Evidence of these landmass collisions and splits comes from fossils, landform shape, features, and rock structures, and climate change

Changes in Landform areas over Geologic Time Landmass changes can occur at hot spots within lithospheric plates; Earth’s landmasses will continue to move and change during the geologic time of the future.

Causes of Plate Tectonics

Convection Currents Hot magma in the Earth moves toward the surface, cools, then sinks again. Creates convection currents beneath the plates that cause the plates to move.

Convection currents deep inside Earth can cause the asthenosphere to flow slowly carrying with it the plates of the lithosphere.