Transcript Introduction to Plate Tectonics

Introduction to Plate Tectonics
`
Continental Drift
According to the theory, the continents were once a part of a super continent.
The supercontinent was known as Pangaea, which means "all land."
The theory proposes that the
continents starting breaking
apart and drifting until they
reached their current positions
today.
Evidence to Support Continental Drift
1) Similar Fossils
2) Types of Rocks
3) Glaciation Patterns on surfaces that were widespread
The key was that the fossil evidence included organisms found on several
different landmasses.
Example: Mesosaurus, a reptile,
was found in South America
and Southern Africa.
Evidence to Support Continental Drift
Rock types that are found in continents oceans apart are further evidence
to support continental drift.
Example: Matching mountain ranges in North America and Scandinavia.
Ancient Climates provide further support:
Glacial deposits have been found in areas that today have tropical
climates, this suggests that they were once connected.
The main objection to this hypothesis was that at the time a
mechanism could not be described that would cause this shift.
Sea Floor Spreading
A hypothesis by Hess that states the following:
In this process, new ocean floor forms along Earth's mid-ocean ridges, slowly moves
across ocean basins, and finally sinks below the mantle in the deep ocean trenches.
These ridges are thought to have formed from oceanic
volcanic eruptions.
Evidence for sea floor spreading includes magnetic strips in the ocean floor,
earthquake patterns, and measurements of the ages of rocks on the ocean floor.
Sea Floor Spreading Explained:
What are magnetic strips?
Rocks that acquire the polarity of the Earth's magnetic field when they
are formed. This is called paleomagnetism.
The magnetite in the rocks are the minerals that help the rocks
become magnetic.
Rocks on opposite sides of an ocean ridge are evidence of sea floor
spreading.
Earthquake Patterns and Ocean Floor Age
Patterns of earthquakes from the subduction of the ocean floor
provide more evidence of sea floor spreading.
In 1968, scientists collected data on both sides of the mid-ocean ridge, the data
confirmed predictions of the age of the ocean floor. The youngest part being on
central valley and the oldest on the subduction zone.
Theory of Plate Tectonics
Click on map to see an introduction to the theory.
The Theory of Plate Tectonics
The theory that the Earth's lithospheric plates move slowly relative to each
other, and it is driven by the convection currents in the Earth's mantle.
The theory explained what Wegener could not, and that was
the there were forces that could set Earth's outer shell in
motion. This was the convection currents.
Effects of plate tectonics - plates move about 5
centimeters per year. This cause earthquakes,
volcanoes, and the formation of mountains.
Types of Plate Boundaries
Plate boundaries are where the movement of plates occur.
Divergent Boundaries: Are formed where the plates diverge or move apart.
* Oceanic lithosphere is formed here.
Convergent Boundaries: Are formed where the plates converge or move
together.
* Lithosphere can be destroyed here.
Transform Fault Boundaries: occur where two plates
grind past each other.
*Lithosphere is not created or
destroyed
here.
Convergent Plate Boundaries
Divergent Plate Boundaries
Transform Fault Boundaries
Divergent Plate Boundaries
Most are located along the mid-ocean ridges.
This is where new lithosphere is created.
Example: Rhine Valley in Northwestern Europe.
Click on object for an animation of divergent plate
action.
Convergent Plate Boundaries
Plates collide and interact, producing volcanoes, trenches, and mountain
ranges.
This area is also sometimes known as "destructive plate margins" because
lithosphere is often destroyed here.
Click on picture to link
to animation.
Types of Convergent Boundaries
Oceanic - Continental: Oceanic lithosphere is subducted
beneath a continental plate.
Oceanic - Oceanic: one oceanic plate is
subducted beneath another oceanic plate.
Continental - Continental: conversion of
two continental plates cannot be
subducted so mountain ranges form.
Transform Fault Boundaries
Plates slide past each other without destroying the lithosphere.
These faults can produce intense
earthquakes.
Click on object for animation.
What type of plate movement or boundaries are shown?
Click on the flashing images to begin.
Resources:
Youtube.com
Google images
Georgia, Prentice Hall, Earth Science
Tarbuck, Lutgens, 2009