Sea Floor Spreading

Inside EarthCh. 1.4

Introduction

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

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___.