Transcript Sea Floor Spreading

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 midocean 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___.