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Sea-Floor Spreading
Sea-Floor Spreading
Tubeworms have no
mouth, eyes, or
stomach ("gut").
Their survival
depends on a
symbiotic
relationship with the
billions of bacteria
that live inside of
them. These
bacteria convert the
chemicals that shoot
out of the deep sea
vents into food for
the worm.
Sea-Floor Spreading
Sonar - a device
that bounces
sound waves off
under-water
objects and then
records the
echoes of these
sound waves. The
time it takes for
the echo to arrive
indicates the
distance to the
object.
Sea-Floor Spreading
Mid-Ocean Ridge – the longest chain of
mountains in the world---these are
divergent plate boundaries.
Sea-Floor Spreading
Sea-Floor
Spreading –
Harry Hess in
the 1960’s; the
process that
continually
adds new
material to the
ocean floor
while pushing
older rocks
away from the
ridge
 Ocean floor moves like a conveyor belt
carrying continents with it.
 New ocean floor forms along cracks in
the ocean crust as molten material erupts
from the mantle spreading out and
pushing older rocks to the sides of the
crack.
 New ocean floor is continually added by
the process of sea-floor spreading.
Sea-Floor Spreading
1. Evidence from
Molten Material –
Rocks shaped like
pillows(rock pillows)
show that molten
material has
erupted again and
again from cracks
along the mid-ocean
ridge and cooled
quickly
Evidence #1: Molten Material
 The submersible, Alvin,
found strange rocks
shaped like pillows or
like toothpaste
squeezed from a tube.
 Such rocks can form
only when molten
material hardens
quickly after erupting
under water.
http://www.youtube.com/watch?v=
gn_IW5Vsxaw
Sea-Floor Spreading
Sea-Floor Spreading
2. Evidence
from Magnetic
Stripes – Rocks
that make up
the ocean floor
lie in a pattern
of magnetized
stripes which
hold a record of
the reversals in
Earth’s magnetic
field
Evidence #2: Magnetic Stripes
 Scientists discovered
that the rock that makes
up the ocean floor lies
in a pattern of
magnetized “stripes”.
 They hold a record of
reversals in Earth’s
magnetic field.
Sea-Floor Spreading
Earth's magnetic field comes from this ocean of
iron, which is an electrically conducting fluid in
constant motion
Supercomputer models of
Earth's magnetic field.
Sea-Floor Spreading
3. Evidence
from Drilling
Samples – Core
samples from the
ocean floor show
that older rocks
are found farther
from the ridge;
youngest rocks are
in the center of
the ridge
Sea-Floor Spreading
Subduction –
Process by
which the ocean
floor sinks
beneath a deepocean trench
and back into
the mantle; this
part of the
ocean floor
melts in the
process
Sea-Floor Spreading:
Subduction zone
Deep-Ocean
Trench –
Occurs at
subduction
zones. Deep
underwater
canyons form
where oceanic
crust bends
downward
Sea-Floor Spreading
http://www.wwnorton.com/college/geo/egeo/animations/ch2.htm
http://science.discovery.com/videos/100-greatest-discoveries-shortsmagnetic-field-reversal.html
http://www.youtube.com/watch?v=4LoiInUoRMQ&feature=fvw
http://www.youtube.com/watch?v=6CsTTmvX6mc