All of the phenomena that we will discuss over the next month are all a result of plate tectonics.

Plate Tectonics is the idea that the Earth is broken up into a number of plates. These plates have been, and are currently moving over the face of the Earth. Some are pulling away, some are pushing together, and others are sliding by one another.

The majority of volcanic eruptions and earthquakes are the direct result of this plate motion..

Alfred Wegener…. (The Father of Continental Drift…)

Was the first to come up with the idea that the continents were moving…

His theory is known as… Continental Drift… -

Earths continents are in motion……

Pangea…. Alfred Wegner also

believed that at one time in the past, all of the continents were once fit together.

He called this “Super Continent”……..

Pangea.

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…

Was Wegner’s idea accepted ???NOOOOOO ! ! ! !

Why ? ?

He could not explain what is making them move ! !

Seafloor Spreading Wegener believed only the

continents were moving around the globe while plowing through the ocean floor

How could they move through something that was solid?

Technology allowed scientists to map the sea floor and they found that the sea was not completely flat

There were deep canyons, huge mountains, etc.

How did they form?

Seafloor Spreading Harry Hess proposed

that sea floor was being formed at ridges and by intruding magma

This pushes older ocean floor further and further apart

Trenches were the sites where ocean crust was destroyed

What is Moving the Plates?

Convection Currents

Evidence for Sea Floor Spreading Age of the rocks

As you go away from the ridge the rocks get progressively older

Evidence for Seafloor Spreading The pattern of

normal and reverse magnetism Mirror images on

either side of the ridge

Plate Movement The Earth is divided

into many layers Crust, Mantle, Core

However there are other layers

Lithosphere – solid, crust and upper mantle

Asthenosphere – partially molten and will flow, part of the mantle

Convection Heat from the core of

the earth rises, cools and sinks

This puts the asthenosphere in motion

The overlying plates are then put into motion as well

Types of Plate Boundaries Convergent – Plates moving towards one

another

Divergent – Plates moving away from one another

Transform – Plates move side by side

Divergent Plate Boundaries Forms a rift valley

where the plates are splitting apart

Examples: Mid-Atlantic Ridge East African Rift Valley

Convergent Plate Boundaries Can form mountain ranges/volcanoes Types

Continent-Continent collisions

Ocean-Continent collisions

Ocean-Ocean collisions

Continent-Continent collisions Rocks have the same

densities on either plate so upon collision the rocks go up. Example: Himalaya

Mountain Range Indo-Australian Plate

and the Eurasian Plate

Continent-Ocean Collisions The 2 plates of different

densities so the plate with higher density goes underneath the plate with the lower density

This is called subduction The oceanic plate goes

deeper and deeper until it melts and eventually gets erupted from volcanoes

A trench is formed where the subduction occurs

Examples of continent-ocean collisions Nazca plate – South

American plate

Results in the Andes Mountains

Juan de Fuca plate and the North American plate

Creates the Cascade Range

Ocean-Ocean collisions Subduction still

occurs because the older of the ocean plates will have a higher density

Creates volcanic islands Example: Pacific Plate

and the Eurasian Plate Creates the Japanese

Volcanic Island Arc

Transform Boundaries Plates are sliding

past Can create

mountains Example: Pacific

plate and the North American plate

The boundary between these two is known as the San Andreas Fault