Download Intro to Plate Tectoncis

Earth Science Notes
• Take a second and write about
the knowledge of plate tectonics
you already have.
Objectives
I can…
• Intelligently talk about the Theory of Plate
Tectonics.
• Describe the development of the theory from its
origins to the present day accepted theory.
• Discuss problems with the initial theory.
• Explain the believed caused to moving tectonic
plates.
WHAT IS CONTINETAL
DRIFT?
• The theory that
continents move slowly
about the earth's surface,
changing their positions
relative to one another
and to the poles of the
earth.
WHAT IS CONTINETAL
DRIFT?
• Original theory was
proposed by Alfred
Wegener.
– He thought that each
continent was
propelled like a ship
through the solid
ocean floor.
WHAT IS CONTINETAL
DRIFT?
• Wegener's theory
was based on
previous
observations about
the Coast lines of
South America
and Africa.
– The two continents
looked like they fit
together
CONTINETAL DRIFT / PLATE
TECTONICS?
• Continental Drift represents a total shift of
scientific thought.
– The prevailing view was that the continents
had always had the same positions on the
planet that they do today. This is a very
logical view.
– Wegener attempted to provide convincing
evidence that, over long periods or geological
time, the continents moved across the surface
of the earth. This was a radical view.
WHAT IS CONTINETAL
DRIFT?
• To support the theory Wegener obtained
various lines of evidence.
– Geological data
– Climate Data
– Fossil Data
We will discuss this further
next class.
• Theory was not accepted because…
– Scientist were skeptical of continents moving
through rock
– It had no mechanism (apparent cause).
CONTINETAL DRIFT / PLATE
TECTONICS?
• Like we said, there was no mechanism for moving
continents.
• This was changed when we began mapping the
ocean floor and developed the theory of seafloor
spreading.
– We will discuss seafloor spreading later.
• As evidence began to accumulate and a mechanism
had been proposed for how the continents move,
the theory gained traction and developed further. It
is now referred to as the Plate Tectonic Theory.
WHAT IS PLATE TECTONICS?
• A theory explaining the structure of the
Earth's crust and many of the associated
events (e.g. volcanoes and earthquakes)
resulting from the interaction of rigid
lithospheric plates that move slowly over
the underlying plastic-like mantle.
What is Plate Tectonics
• Write about the origin of the Plate Tectonic
Theory.
– Who first proposed it?
– What is the basic idea of it?
– How has it changed?
– Is there any other information that you think
may be important?
CONTINETAL DRIFT / PLATE
TECTONICS?
• Plate tectonics was originally called the “Theory
of Continental Drift.”
– The development of the theory is an excellent
example of the application of the scientific method.
Obs.  Inference  Hypothesis  Test (measurements)
 Results (data analysis)  Conclusion (theory).
S.A. and Africa  continents move  Continental Drift
 look for evidence  geo formations match up 
Plate Tectonic Theory.
Main Features of Plate Tectonics
• The Earth's surface is covered by a series
of crustal plates.
Main Features of Plate Tectonics
• The tectonic plates are made up of the
Earth’s crust and the upper part of the
mantle layer underneath.
Main Features of Plate Tectonics
• Lithosphere – top layer of the Earth made up of the
crust and the top part of the mantle.
• Asthenosphere – solid but plasticlike layer on which the
lithosphere sits.
– Movement in this layer actually creates movement in
the plates.
Main Features of Plate Tectonics
• The ocean floors are continually, moving,
spreading from the center, sinking at the
edges, and being regenerated.
Main Features of Plate Tectonics
• Convection currents beneath the plates
move the crustal plates in different
directions.
Main Features of Plate Tectonics
• The source of heat driving the convection
currents is radioactivity deep in the
Earths mantle.
Main Features of Plate Tectonics
• What are some of the structural
components of the Plate Tectonic Theory?
• Describe the different parts of the Earth
involved in the process of moving
continents.
How Plates Move
• Heat from core
causes magma to
expand and rise
• Magma near the
surface cools and
condenses and
falls
• This creates
convection cells
How Plates Move
• Hot magma rises
to the surface at
spreading ridges
and forms new
crust.
• new crust pushes
the rest of a plate
out of its way.
How Plates Move
• Old parts of a plate
sink down into the
mantle at
subduction zones
because they are
colder, thicker and
denser than the
warm mantle
material
underneath them.
How Plates Move
• Describe the mechanism for continental
drift that Alfred Wegener’s original theory
was missing. Why do crustal plates
move?
Quick Summary of PT Theory
• Earth is made of plates
– Plates are made up of crust and upper mantle
• The Lithosphere
• These Plates move
– Lithosphere sits on the Asthenosphere
• When the Asthenosphere moves the plates moves
• Plate movement is caused by convection cells
– Convection cells are created by the heating and
cooling cycle of magma
– Radioactivity deep within the earth is the source of
heat
Lastly
Identify some concepts in this lesson
that seem relate to relate to material from
previous units. What concepts are we
using to describe the process we talked
about today?