Download Magnetic Field, Sea-floor Spreading, Deep

MAGNETIC FIELD
Some of our most important evidence of
sea-floor spreading comes from magnetic
reversals recorded on the ocean floor
The magnetic poles can change place
(called magnetic reversal)
Magnetic mineral grains line up in opposite
direction of magnetic field
EARTH’S MAGNETIC FIELD
If you could cover our entire planet
with iron filings, they would form a
similar pattern
MID-OCEAN RIDGES
• Mid-ocean ridge- an undersea
mountain chain where new
ocean floor is produced
• Sonar is used to map the ocean
floor
• Most mountains in mid-ocean
ridge are under hundreds of
meters of water
• Iceland is part of a mid-ocean
ridge that rises above the
surface
Harry Hess (geologist) examined maps of mid-ocean ridges and thought: Maybe
Wegener was right about continental drift!
Process of Sea-floor Spreading
Sea floor spreads apart along both sides of
mid-ocean ridge
Magma flows to the opening and then cools to
form new sea floor.
Sea floor continues to spread apart as new
crust is added. Processes repeats like a
conveyor belt, carrying continents along with
them.
EVIDENCE FOR SEA-FLOOR
SPREADING
Evidence supported Hess’s theory of sea-floor spreading: eruptions of
molten material, magnetic stripes in the rock of the ocean floor, and
the ages of the rocks themselves.
Because of sea-floor
spreading, the distance
between Europe and North
America is increasing by a
few centimeters per year.
SUBDUCTION AT DEEP-OCEAN
TRENCHES
• Ocean floor doesn’t just keep
spreading
• part of the ocean floor sinks
back into the mantle through
deep-ocean trenches.
Sea-floor Spreading
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Key Terms DUE TOMORROW
1. Fault
2. Divergent boundary
3. Convergent boundary
4. Transform boundary
5. Rift Valley