Power point 9.4
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Transcript Power point 9.4
Sea-Floor Spreading
Chapter 9, Section 4
•The Mid-Ocean Ridge
Longest mountain chain in the
world
It is almost entirely under water,
but some areas do peak out of
the ocean.
•Example – Iceland
Sea-Floor Spreading
As new rock
emerges from
the rift valley,
older rock is
pushed towards
the edge of the
ocean.
http://www.wwnorton.
com/college/geo/egeo
/animations/ch2.htm
Evidence for S.F.S.
Molten Material –
• Pictures of molten material rising
from the mid-ocean ridge have
been taken.
The molten material cools very
quickly due to the contact with cold
ocean water.
http://www.wwnorton.com/college/geo/egeo/animations/ch2.htm
Evidence for S.F.S.
• Magnetic Stripes in the ocean floor
Earth’s magnetic poles (caused by the inner
core spinning) have reversed themselves in
the past.
If they reverse again, our compasses will
point south.
http://www.wwnorton.com/college/geo/egeo/animati
ons/ch2.htm
Evidence for S.F.S.
Drilling Samples
•Scientist drilled the sea-floor to
get rock samples.
The older rocks were found far
from the mid-ocean ridge.
The younger rocks were found
near the mid-ocean ridge.
Subduction at Deep-Ocean
Trenches
Subduction
means to sink
below.
This allows the
ocean floor to
sink back into
the mantle…a
recycling of
sorts.
http://www.wwnorton.com/college/
geo/egeo/animations/ch2.htm
Subduction and Earth’s
Oceans
The Pacific Ocean is SHRINKING!!!
• More oceanic crust is subducted
than is being produced, because
there are more trenches.
The Atlantic Ocean is
GROWING!!!
• More oceanic crust is being
produced than subducted because
there are fewer trenches.