Sea Floor Spreading Inside Earth

Ch. 1.4

Introduction

�  A. Deep in the ocean the temp is near _freezing_(0°C)

�  B. Many things live in the deep ocean.

�  1. Giant __tubeworms_ and clams

�  2. Provide evidence for Wegener’s hypothesis of __Continental Drift__.

�  500 × 340 - nsf.gov

�  500 × 340 - nsf.gov

I. Mid Ocean Ridges

� A. Sonar = device that bounces sound waves off underwater objects and records them 

� B. Mid-ocean ridges are _mountain chains underwater and the island of Iceland.

� C. Mapping the ridges makes scientists want to know more about them.

II. What is Sea Floor Spreading

�  A. _Harry Hess_ an American geologist studied mid-ocean ridges.

�  B. His idea was of sea-floor spreading that continually adds new __material___ to the __ocean floor.

Sea Floor

� C. Sea floor spreads apart along both sides of mid-ocean ridge as __new crust is added.

� D. As the ocean floor moves, the _continents_ move too.

� E. _Older_ rock gets pushed further out from the ridge.

Sea Floor

III. Evidence from Sea Floor Spreading

� A. Molten Material

�  1. A submarine, Alvin went to the ocean floor to find evidence of sea-__floor__ _spreading__. Molten material is erupting from the mantle and hardens quickly when it hits the cold ocean water.

Evidence

� B. Magnetic stripes

�  1. Scientists found that the rock makes up the ocean floor lies in patterns of _magnetized__ “stripes”.

�  2.These stripes hold a record of __reversal___ in Earth’s magnetic field.

Evidence

� C. Drilling samples

�  1. Drilling into oceanic rock has given us the _ages_ of the rock.

�  2. Scientists determined that the _youngest__ rocks were __closest__ to the center of the mid-ocean ridges and the older rocks were farther away from the ridges.

IV. Subduction at the Trenches

�  A. deep ocean trenches = underwater canyon

�  B. Subduction = ocean floor moves back into the mantle through deep ocean trenches

� 

Subduction

� C. Subduction and Earth’s oceans

�  1. Pacific Ocean is __Shrinking__;

�  2. Atlantic Ocean is _Expanding___.