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

• Theory was not accepted because…– Scientist were skeptical of continents moving

through rock– It had no mechanism (apparent cause).

We will discuss this further next class.

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?