Transcript A) What is the process of sea-floor spreading?

At what places does material from Earth’s interior flow out onto the surface?
What causes lava to harden?
EQ:
A) What is the process of sea-floor
spreading?
B) What happens to the ocean floor at
deep ocean trenches?
C) How does sea-floor spreading
support Wegener’s theory of
Continental Drift?
Mid 1900s
used sonar
1) Sonar- device that uses sound waves to detect
objects.
2) The Mid-Ocean Ridge
longest chain of mountains in the world
found mainly in the Atlantic, Pacific, and Indian
Oceans
mostly under hundreds of meters of water, but
not entirely
Harry Hess, a scientist who
studied the mid-ocean ridge,
reconsidered Wegener’s
idea, and in 1960 proposed
radical idea that the ocean
floors move like conveyor
belts, carrying the continents
along with them. Hess called
the process sea-floor
spreading
Sea-floor spreading- the process that continually
adds new material to the ocean floor
molten rock erupts through crack
older rock is pushed aside
Molten rock cools to form strip of rock
rock
subducts
molten
rock cools
Molten rock cools
to form
to form strip strip
of rockof
rock
molten
rock
erupts
through
crack
older rock
is pushed
aside
1) Evidence from molten material
2) Evidence from magnetic stripes
-- in
in the
the past
past a
a compass
compass needle
needle would
would have
have pointed
pointed south.
south.
- rock on the ocean floor lies in a pattern of magnetized stripes
- rocks that harden at the same time have the same
“magnetic memory”
- the pattern of stripes are the SAME on both sides of the
mid- ocean ridge
3) Evidence from drilling samples
The Glomar Challenger
was the first research
ship designed to drill
samples of rock form the
deep-ocean floor.
3) Evidence from drilling samples
a) the farther away from the ridge that the samples
were taken, the older they were, and the youngest
samples were always in the center of the ridge
1) Subduction- the process by which the ocean
floor sinks beneath a deep-ocean trench
2)Deep-ocean trench- forms where the oceanic
crust bends downward
at deep ocean trenches, subduction allows part of the
ocean floor to sink back into the mantle
1) Subduction in the Pacific Ocean
a) Pacific Ocean is shrinking
2) Subduction in the Atlantic Ocean
a) Atlantic Ocean is expanding