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. Click on object for animation. These faults can produce intense earthquakes.

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