Plate Tectonics: A whole new way of looking at your planet
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The Book  
Table of Contents
Introduction
In the Beginning
The Tectonic Plates
Mount St. Helen
How Plates Move
Plate Boundaries
A Changing Earth
Pangaea - All Lands
Mid-Ocean Ridges
An Ocean is Born
The Birth of an Island
Mountain Ranges
Subduction Zones
Island Arcs
The Ring of Fire
Faults
Earthquakes
Hot Spots
Mantle Plumes
Origin of Life Theories
Global Climate
Other Worlds
Welcome to Your World

How Plates Move

Powered by forces originating in Earth’s radioactive, solid iron inner core, these tectonic plates move ponderously about at varying speeds and in different directions atop a layer of much hotter, softer, more malleable rock called the athenosphere. Because of the high temperatures and immense pressures found here, the uppermost part of the athenosphere is deformed and flows almost plastically just beneath the Earth’s surface. This characteristic of the athenosphere to flow allows the plates to inch along on their endless journeys around the surface of the earth, moving no faster than human fingernails grow.
Convection cells in the Earth's mantle drive the motion of tectonic plates on the surface One idea that might explain the ability of the athenosphere to flow is the idea of convection currents. When mantle rocks near the radioactive core are heated, they become less dense than the cooler, upper mantle rocks. These warmer rocks rise while the cooler rocks sink, creating slow, vertical currents within the mantle (these convection currents move mantle rocks only a few centimeters a year). This movement of warmer and cooler mantle rocks, in turn, creates pockets of circulation within the mantle called convection cells. The circulation of these convection cells could very well be the driving force behind the movement of tectonic plates over the athenosphere.
   
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