Download Notes 9-4 Sea Floor Spreading Name p. 331

Notes 9-4 Sea Floor Spreading
Name _____________________________
p. 331-337
Period _____ Date __________
Even though there is no light and freezing temperatures at the depths of the ocean, the ocean floor is still
teeming with _____________. At the East Pacific Rise, ocean water sinks through ________________, or
______________ in the crust. The water is heated by contact with hot material from the
_____________________.
Bizarre creatures have been discovered at the hot-water _________________. This has provided scientists with
______________________ that supports Wegener’s hypothesis of _________________ __________________.
Mapping the Mid-Ocean Ridge
The longest chain of mountains in the world is the _________________________________. Scientists started
mapping this mountain range in the mid-1900s using ____________________. (a device that bounces
__________________ waves off underwater objects & records the echoes)
Parts of the mid-ocean ridge poke above the surface. For example, the island of _______________________.
A valley, almost twice as deep as the Grand Canyon splits the ___________ of the mid-ocean ridge.
Evidence for Sea-Floor Spreading
___________________ _______________, an American geologist began studying maps of the mid-ocean ridge
& reconsidered Wegener’s idea.
In 1960, Hess suggested that at the mid-ocean ridge, molten material _____________ from the
________________ and erupts. The molten material then _____________________ out, pushing
_________________ rock to both sides of the ridge.
Hess called the process that continually adds new material to the ocean floor _________-______________
_____________________.
Three types of evidence support Hess’ theory
1.
Evidence from ________________ ____________________: in the 1960s, scientists explored the
ocean floor in Alvin and found that new material is ___________________ along the mid-ocean ridge.
Rocks shaped like pillows or toothpaste can only form when molten material hardens
_________________ after erupting under water.
2. Evidence from _________________ _______________________: Earth’s magnetic poles reverse
themselves over time. The rock that makes up the ocean floor lies in a pattern of magnetized “stripes”.
These hold a record of _____________________ in the magnetic field. Molten material contains
_____________, which lined up in the direction of Earth’s magnetic poles when it cooled. This locked
in a “magnetic memory” in the rocks on the ocean floor.
3. Evidence from _______________ _______________________: The Glomar Challenger sent drilling
pipes through water ____ km deep in 1968. Samples from the sea floor allowed scientist to determine
the ages of rocks. Scientists found that the __________________ away from the M-OR, the
____________________ the rocks. The youngest rocks were always in the __________________ of the
ridge.
Subduction at Deep-Ocean Trenches
Ocean floor does not continue to get wider due to underwater canyons called ________________________________ ________________________. A deep ocean trench forms where the oceanic crust bends
_________________________.
____________________________ takes place at the deep-ocean trenches. This is the process by which the
ocean floor sinks beneath a deep-ocean trench and back into the _____________________.
________________________ _______________________ under the lithosphere push new crust that forms at
the MOR ____________________ from the ridge and toward a DOT (deep-ocean trench).
New oceanic crust is _____________. But as it moves away from the MOR, it cools & becomes more
__________________. Eventually, ____________________ pulls the older, denser crust down the trench.
At DOTs, subduction allows part of the ocean floor to sink back into the mantle in a process that takes tens of
_____________________ of years.
Subduction & Earth’s Oceans
Subduction & sea-floor spreading can change the ______________ & __________________ of the oceans.
Pacific Ocean: it is ___________________. How? A deep ocean trench __________________more crust than
the MOR can _____________________!
Atlantic Ocean: it is _______________________. It only has a ___________ short trenches. The spreading
ocean floor has nowhere to go! So the continents move also & the whole ocean gets ________________.