Name: _______________________________ Date: ______________ Period:_________
Sea-Floor
Spreading
 Mapping the Mid-Ocean Ridge
 The mid-ocean ridge is the longest chain of ____________________________
in the world.
 Scientists mapped the mid-ocean ridge using __________________________.
 Sonar is a device that bounces sound waves off underwater objects and
records it.
 Describing Sea-Floor Spreading
 At the mid-ocean ridge, ____________________________ material
rises from the mantle and erupts. The molten material
__________________________________, pushing
_________________ rock to both sides of the ridge.
 This process that
_______________________________________________________________ is sea floor spreading.
 Evidence for Sea Floor Spreading: Pillow shaped rocks
 In the 1960s scientists found evidence that
__________________________________________ is erupting along
the
____________________________________________________________.
 The presence of ______________________________________________________________ has
showed that molten material has erupted again and again.
 Evidence for Sea Floor Spreading: Magnetic Reversal
 Evidence in the rocks shows that Earth’s _________________________________________ have
___________________________________________________.
 The iron bits lined up in the ___________________________________________________ shows
this evidence.
 Evidence for Sea Floor Spreading: Age of rocks from drilling samples
 Evidence from _____________________________________ into the sea
floor shows evidence of the _______________________________ of rocks
 The ______________________________ you get to the mid-ocean ridge
the _______________ the rock. The _________________________ you get,
the ______________________ the rock.
 Subduction in Deep-Ocean Trenches
 As the ocean spreads apart, it also plunges into deep water canyons
called
________________________________________________________________.
 Subduction is the process by which the ocean floor ____________________________________
_____________________________________________________________________________.
 Subduction creates new ocean floors
 The processes of subduction and sea-floor spreading
can change the ______________________
______________________________________ of the
oceans.
 Because of this processes, the ocean floor is
_______________________________ about every __________________________ million years.
 Subduction changes the size of the oceans
 The Pacific Ocean is ___________________________________! This is due to the fact that a deepocean trench is _______________________________ more crust than the mid-ocean ridge can
___________________________________.
 The Atlantic Ocean however, is _____________________________________!
Evidence for Seafloor Spreading
Youngest
Oldest
WORD BANK
New
Mid-ocean ridge
1) Age of Fossils:
 Rock samples closest to the mid ocean ridge has the ______________fossils.

Rock samples farthest away from mid ocean ridge has the ______________fossils.

The fossil evidence supports the idea that _______ oceanic crust is forming along the ________.
WORD BANK
North
South
New
Switched
2) Magnetic Fields:
 The Earth’s magnetic poles have ___________ many times.
Spreading

When rocks with magnetic minerals are formed, their minerals point to where the Earth’s magnetic
______________ pole was when the minerals were formed.

Scientist found bands of rock with minerals pointing towards present day _________ and these
alternated with bands of rock pointing towards present day ______________.

This pattern of evidence shows that _______ocean floor is being created and that the seafloor is
_____________.
CHALLENGE
How do the processes of subduction and sea-floor spreading change the size of the oceans?
A. It causes the oceans to get bigger.
B. It causes the oceans to get smaller.
C. The ocean stays about the same size because sea-floor spreading causes the ocean to get
bigger and subduction cause the ocean to get smaller.