Earth Science Historical Introduction Sea Floor Spreading & the Earth’s Magnetic Field.

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Presentation transcript:

Earth Science Historical Introduction Sea Floor Spreading & the Earth’s Magnetic Field

During WWII ► Maps of ocean floor using  Sonar  Magnetometers Harry Hess, a Captain during WWII, gathered data while cruising from battle to battle

Surprising Data ► Deepest areas (trenches) were close to the continents ► Underwater mountain ranges ran through every ocean  Each mid-ocean range had a central valley running down the middle (rift valley)

Dark blue – deepest areas Yellow – shallowest areas

Surprising Data ► Symmetrical patterns of magnetic reversals centered on ocean ridges

The Earth’s Magnetic Field Reverses! ► Reversals are “recorded” as iron- rich lava cools ► Reversals occur every ~200,000 years  We haven’t had one for 700,000 years!

Reversals recorded in lava flow

Age Evidence ► Ocean crust is much younger than continental crust ► Youngest rocks are found closest to ocean ridges

Data provides support for “Sea Floor Spreading” ► Lava erupts at mid-ocean ridges and cools, creating new sea floor ► Sea floor dives back under continental crust at trenches (Subduction Zones)

Process is driven by convection currents within asthenosphere