Continental Drift Theory Flaws

• 1st What force could push large mass over great distances

• 2nd How the continents could move were through something solid like earth’s crust

• They questions were the reasons why Wegener’s theory was rejected until the 1950s

Seafloor Spreading • Until 1900’s most people believed – that the oceans floors were flat – Ocean floor was not changing – Ocean floor was older than continental crust

War and Technological advancement changed all misconceptions

WWII Sub Warfare • Sonar tech was improved in order to create detailed

maps and way to navigate• Magnetometers: device that detect small changes in

magnetic fields, towed behind boats to locate enemy subs

• Data from these sources revealed vast underwater mountain chains called ocean ridges and deep sea trenches

• Text p 474 figure 17.8

Ocean Rocks & Sediment

Rock Analysis• The age of the rocks varies and the

variations were predictable• Samples near the ocean ridges were

younger than the samples taken near the trenches..

Ocean Rocks & Sediment Sediment Analysis

• Thin layers of sediment compared to continents • Thickness of sediment increased with

distance from an ocean ridge

Seafloor Spreading • Theory that explains how new ocean crust is

formed at ocean ridges and destroyed at deep sea trenches

• Vital key that supports Wegener’s continential drift theory

In Class Activity • Turn to p 477 figure 17.13

• • P. 478 read Visualizing Seafloor Spreading

ANY QUESTIONS?