Transcript Sea Floor Spreading

Sea Floor Spreading
The Mid-ocean Ridge
Vocabulary
•Sonar
•Sea-floor spreading
•Deep-ocean trench
•Subduction
•Mid-ocean ridge
60 years ago, in the
1950’s, Sonar was
invented.
http://www.soundsnap.com/tags/sonar
Bats use it!
So do dolphins!
So does this guy!
Sonar brought Wegner’s
theory back to life!
Sonar is a device that bounces
sound waves off underwater
objects and records the echos of
these sound waves. The time it
takes for the echo to arrive
indicates the distance to the
object. It made it possible for
us to observe the ocean floor.
http://www.soundsnap.com/tags/sonar
Soon, scientists observed a large
mountain chain running down the
center of the Atlantic ocean.
They quickly found that the
Mid Atlantic ridge ran
around the world!
Harry Hess :
American Geologist
No! Harry Hess, not
Harry Potter!
Sea-Floor Spreading
• Harry
Hess
Process that continually adds
new material to the ocean floor
while pushing older rocks away
from the ridge.
Process that continually adds
new material to the ocean floor
while pushing
older rocks
away
Moves
like a conveyor
belt
from the ridge.
carrying
continents with it.
New rock forms along the cracks
in the ocean crust as molten
material erupts from the mantle,
spreading out and pushing older
rock to the sides of the crack.
New rock is continually being
added by Sea floor Spreading..
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
trench.
Sea Floor Spreading is the
process…..What is the evidence?
Three key pieces of
evidence!!
#1
Pillow Lava
forms when magma cools in
water. This is evidence of
volcanic activity!
#2
Magnetic
Striping
https://www.geolsoc.org.uk/Plate-Tectonics/Chap3-PlateMargins/Divergent/Mid-Atlantic-Ridge
#3 Drilling for Rock Samples:
This shows you the age of the sea floor. The red
areas are new rocks and the blue areas are the
oldest oceanic rock.
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
• Sonar
• Mid-Ocean Ridge
• ocean is spreading open!!!
• pillow lava
• magnetic stripes
• Drilling rock samples