Download Unit 3: Lesson 2: Theory of Plate Tectonics

+
Unit 4: Lesson 2:
Theory of Plate Tectonics
+
REVIEW
 What
layer of the Earth is broken into tectonic
plates?
 What
layer of the Earth has convection that moves the
plates?
+
Introductory Video
Minute Physics - Plate Tectonics Explained
Describe something new that you learned about
plate tectonics.
https://www.youtube.com/watch?v=kwfNGatxUJI
+
World Map
Do the continents look like they fit together?
+
What evidence suggests that
continents move?
•
Late 1800’s Alfred Wegener – Continental Drift
•
•
Continents once formed a single landmass that broke
up and drifted apart.
Evidence
• Same species on both sides of the Atlantic Ocean
• Location of mountain ranges and rock formations
• Same climate on sever different continents
+
What is Pangaea?
 245
million years ago
 Pangaea - all the continents were one landmass
 Mountains formed as the continents formed Pangaea
 Panthalassa – ocean that surrounded Pangaea
+
What is Pangaea?
 200

million years ago
two continents Laurasia and Gondwana
 Laurasia –
 North America
 Eurasia
 Gondwana –
 South America and Africa
 Antarctica, Australia, India
+
What is Pangaea?
 150

million years ago
South America and Africa began to split form the South
Atlantic Ocean
 India, Australia, and Antarctica began to split
 India moved northward toward Eurasia
65 million years ago - after the move
+
What is Pangaea?

50 million years ago

Continents moved into their present position

Oceans formed and others disappeared

India collided with Eurasia to form the Himalaya Mountains
3 million years ago - after the move
+
Comparing Pangaea to the
modern location of the continents
+
The Theory of
Continental
Drift
+
Support For the Theory
 Mid-Ocean
ridges –huge mountain ranges on the
ocean floor

Led to the theory of plate tectonics, that is based on some
of Wegener’s ideas.
+
Support For the Theory

Age Of the Sea Floor



Youngest rock is closest to the ridge
Oldest rock is furthest away from the ridge
Magnetic Properties of the Sea Floor

Sea-floor rock has magnetic patterns that are the same on
both sides of the ridge.
+
Support For the Theory
 Sea-Floor
Spreading – molten rock from inside
Earth rises through the cracks in the ridges, cools,
and forms new oceanic crust.

The old crust splits in the middle, and the two pieces
moves away from each other
+
Support For the Theory
 Ocean Trenches


– huge trenches in the sea floor
Dense oceanic crust is sinking into the asthenosphere
Old crust is destroyed at the same rate as new crust is forming
The
Theory
of
+
Plate Tectonics
+
What is plate tectonics?
 Plate Tectonics - Large-scale movements of Earth’s lithosphere,
which is made up of the crust and the rigid, upper part of the mantle.
 Tectonic
Plate – pieces of the lithosphere that move on top of the
asthenosphere
+
Major Tectonic Plates
Pacific
North American
Nazca
South American
African
Australian
Eurasian
Indian
Antarctic
+
Plate Boundaries
 Three
types of plate boundaries

Divergent – two plates
move away from each
other

Transform – two plates
move past each other
horizontally

Convergent – two plates
collide
+
Types of Convergent
Boundaries
 Continent-Continent
Collisions:
Two plates of continental lithosphere collide,
 Buckle and thicken
 Forms mountains

+
Types of Convergent
Boundaries
 Continent-Ocean


Collisions:
Oceanic lithosphere collides with continental lithosphere
Oceanic lithosphere subducts because it is denser
 Subduction – the sinking of Earth’s crust under another plate
+
Types of Convergent
Boundaries
 Ocean-Ocean
Collisions:
Two oceanic plates collide
 The cooler, denser plate subducts under the other plate

+
Divergent Plate Boundaries
Two plates that move away from each other
 Forms a mid-ocean ridge or rift valley

+
Divergent Plate Boundaries
Steps to form a mid-ocean ridge
1.
Asthenosphere rises between
the plates
2.
Magma is created when the
lithosphere melts
3.
Lava erupts from between the
plates
4.
Lava cools and hardens to form
new rock on the ocean floor
5.
The new rock is thin, warm, and
lightweight so it sits higher than
the surrounding sea floor
making a ridge.
+
Transform Plate Boundaries
 Two
plates move past each other horizontally
 Edges
do not slide smoothly
 Earthquakes
caused when the plates slip past each other
+
The Driving
Forces of Plate
Tectonics
+
What drives plate tectonics?
 Mantle
convection – movement of material in the mantle as
the hotter parts rise and the cooler sections sink
BUT scientists believe that it doesn’t create the force needed to
move plates
+
What drives plate tectonics?
 Main
Driving Forces

Ridge push – as new crust is formed at mid-ocean ridges it pushes
the crust away from the ridge

Slab pull – when a cold, dense plate subducts under another plate it
sinks and pulls the rest of the plate down with it