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

A Changing Earth

As eons pass, continents and other land masses collide, break apart, and drift across the planet on the fiery mantle beneath, opening and closing oceans along the way. Subsequently, their relative position to the equator, the poles, and each other changes over long periods of time. For instance, Africa’s Sahara Desert once lay at the South Pole while the equator ran diagonally across North America.

Continental Drift by USGS.org

Scientists hypothesize that North and South America must have been 6,000 miles apart 450 million years ago. Yet, 250 million years later, they lay locked together as part of Pangea, the great supercontinent. Then a great rift developed between them and today’s Atlantic Ocean began to open. [The plates don’t move very quickly. But consider this: Two inches per year - a typical speed - adds up to 30 miles in one million years. It took only 150 million years for a slight fracture in an ancient continent to turn into today’s Atlantic Ocean].

While the Atlantic Ocean opened, the Pacific began to shrink. The Americas slid west while the huge Eurasian plate and Australia drifted east along with India, which broke away from southern Africa to begin it’s long journey north. Some 20 million years later India collided with southern Eurasia, thrusting up their crustal borders, marking the birth of the majestic Himalayan mountain range. And long ago Ireland and northern Scotland were part of North America, attached to Newfoundland, while part of Florida lay in Africa.
   
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