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Sea Floor Spreading
The Mid-ocean Ridge
•Sea-floor spreading
•Deep-ocean trench
•Mid-ocean ridge
60 years ago, in the
1950’s, Sonar was
Bats use it!
So do dolphins!
Sonar brought Wegner’s
theory back to life!
Soon, scientists observed a large
mountain chain running down the
center of the Atlantic ocean.
They quickly found that the
ridge ran around the world!
Harry Hess :
American Geologist
No! Harry Hess, not
Harry Potter!
Sea-Floor Spreading
• Harry
• An American
geologist who
studied mid-ocean
• He suggested that
the ocean floors
move like conveyor
belts, carrying the
continents along
with them.
Pillow Rock forms when
magma cools in water. This is
evidence of volcanic activity!
This shows you the age of the sea floor. The red areas
are new rocks and the blue areas are the oldest oceanic
Iceland is spreading
open on the MidAtlantic Ridge!
Can you see where the Mid-Atlantic Ridge bisects Iceland?
This is a rift valley!
Sea Floor Spreading
• pillow lava
• magnetic stripes
• Drilling rock samples
If new crust is being added to
Earth’s surface, is Earth
getting bigger?
Subduction is a process
where the ocean floor sinks back
into the mantle at a deep ocean