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

Layers of the Earth Crust Mantle Inner core Outer Core Solid Liquid Lithosphere Athenosphere Inner core Solid Outer Core Liquid

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”

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

Questions... What is the theory of plate tectonics? What is the lithosphere? What is the asthenosphere? What is the connection between the two? What are the two types of plates?

Causes of Plate Tectonics

Convection Currents Plates move by the transfer of heat through heated material. 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.

Questions... What causes plates to move? How is a convection current formed?

Plate Boundaries

Major Plate Boundaries Earth has 6 major plate boundaries Eurasian N. American Pacific S. American African Antarctic

Plate Boundary Types

1. Divergent Boundaries   Boundary between two plates that are moving apart or rifting   RIFTING causes SEAFLOOR SPREADING At the mid-ocean ridge moves 6 cm/year

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

2. Transform Fault Boundaries Boundary between two plates that are sliding past each other Moving in opposite directions Moving in same directions at different speeds EARTHQUAKES along faults Ex: San Andreas fault in CA

San Andreas Fault, CA

3. 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 more dense plate slides under the less dense plate VOLCANOES occur at subduction zones Earthquakes are common

Andes Mountains, South America

Type 2 Ocean plate colliding with another ocean plate The more dense plate slides under the less dense plate creating a subduction zone called a TRENCH May form volcanoes a.k.a. volcanic island arc

Aleutian Islands, Alaska

Type 3 Two continental plates collide: the Continental rocks buckle & rise Have Collision Zones: a place where folded & thrust faulted mountains form Earthquakes are common Little volcanic activity Continental motion occurs 1-5 cm/year

Questions... What are the three types of boundaries? What direction do plates go for each? Which boundary has a subduction zone…what occurs at a subduction zone?

Alfred Wegener In 1915, German geologist Dr. Alfred Wegener proposed an idea called the Theory of Continental Drift. Said all continents were joined together about 250 million years ago as a supercontinent Pangea (“all land”). Eventually Pangea split and moved into current positions

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…

Evidence A system of underwater mountain chains or mid-ocean ridges, rise thousands of meters above ocean floor Caused by plate movement called sea-floor spreading at a divergent boundary Youngest ocean floor rocks – near mid ocean ridges Oldest near the edge of the continents When the sea floor reaches a continental boundary, it is forced downward beneath the continental, called a sea floor trench