AUFC+1.4

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Vocabulary
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 * mid-ocean ridge**: the largest chain of mountains in the world
 * sonar**: a device that bounces sound waves off under water objects and then records the echoes of the waves to determine how far the object is
 * sea-floor spreading**: the process that continually adds new material to the ocean-floor
 * deep-ocean trenches**: forms where the oceanic crust bends downwards
 * subduction**: the process by which the ocean floor sinks beneath a deep-ocean trench and back into the mantle

Introduction

 * strange enviorment provides the best evidence for continental drift

Mapping the Mid-Ocean Ridge

 * they use sonar to map the ocean
 * Iceland is part of the mid-ocean ridge
 * twice as deep as grand canyon
 * scientists curious about how the mid-ocean ridge got there

Evidence for Sea-Floor Spreading

 * Sea-Floor Spreading
 * ocean floors carry continents with them
 * molten material rises from the mantle and erupts
 * molten material spreads out, pushing older rock to both sides of a ridge

Molten Material

 * molten material erupts again and again

Magnetic Stripes

 * patterns of rock show more evidence
 * 780,000 years ago magnetic poles reversed
 * holds a record of the earth's magnetic field

Drilling Samples

 * They drill holes in the ocean floorro determine how old the rock is
 * rocks closer ro ridges are younger
 * rocks farther from a ridge are older
 * shows that sea floor spreading has really taken place

Subduction at Deep Ocean Trenches

 * can change size and shape of oceans
 * the subduction at the Pacific Ocean is making it shrink
 * the subduction at the Atlantic Ocean is making it expand
 * as the Atlantic expands, the continents move with it

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