1) Tubeworms survive through a symbiotic relationship with bacteria that live inside them. The bacteria convert chemicals from deep sea vents into food for the worm. 2) Sonar uses sound waves to determine the distance to underwater objects by measuring the echo return time. 3) Sea-floor spreading was discovered by Harry Hess in the 1960s and explains how new ocean crust continually forms at mid-ocean ridges, pushing older rocks away.

1. Sea-Floor SpreadingSea-Floor Spreading

2. Sea-Floor SpreadingSea-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.

3. Sea-Floor SpreadingSea-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.

4. Sea-Floor SpreadingSea-Floor Spreading
1.1. Mid-Ocean RidgeMid-Ocean Ridge – the longest chain– the longest chain
of mountains in the world---these areof mountains in the world---these are
divergentdivergent plate boundaries.plate boundaries.

5. Sea-Floor SpreadingSea-Floor Spreading
3. 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

6. Sea-Floor SpreadingSea-Floor Spreading

7.  Ocean floor moves like aOcean floor moves like a conveyorconveyor beltbelt
carrying continents with it.carrying continents with it.
 NewNew ocean floorocean floor forms along cracks informs along cracks in
the ocean crust as molten material eruptsthe ocean crust as molten material erupts
from the mantle spreading out andfrom the mantle spreading out and
pushingpushing older rocksolder rocks to the sides of theto the sides of the
crack. New ocean floor is continuallycrack. New ocean floor is continually
added by the process ofadded by the process of sea-floorsea-floor
spreading.spreading.

8. Sea-Floor SpreadingSea-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

9. Sea-Floor SpreadingSea-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

10. Sea-Floor SpreadingSea-Floor Spreading

11. Sea-Floor SpreadingSea-Floor Spreading

12. Sea-Floor SpreadingSea-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

13. Sea-Floor SpreadingSea-Floor Spreading
8. Subduction –
Process by
which the ocean
floor sinks
beneath a deep-
ocean trench
and back into
the mantle;
allows part of
the ocean floor
to sink back
into the mantle

14. Sea-Floor Spreading:Sea-Floor Spreading:
Subduction zoneSubduction zone
Deep-Ocean
Trench –
Occurs at
subduction
zones. Deep
underwater
canyons form
where oceanic
crust bends

15. Sea-Floor SpreadingSea-Floor Spreading