Download Inside Earth - Davis` Dazzlers

Inside Earth:
Chapter 1: Plate Tectonics
Section 4: Sea-Floor Spreading
Vocabulary:
Mid Ocean Ridge: The longest chain of mountains in the world; runs under
Earth’s oceans
Sonar: device used to map mid-ocean-ridge; bounces sound waves off underwater
objects and records the echoes of their sound waves
Sea-Floor Spreading: a process that continuously adds new material to the ocean
floor
Deep-ocean trenches: deep underwater canyons that forms where the oceanic
crust bends downward
Important Facts:
 Sea Floor Spreading
o At the mid-ocean ridge, molten material rises from the mantle and
erupts. The molten material then spreads out, pushing older rock to
both sides of the ridge. The molten rock cools and forms new land
(salt) as the plates move. The older plate sinks below the other
plate and can make mountains and/or islands which will be
volcanic
o Force within Earth allows new oceanic crust to form (convection
current)
o Iceland is a part of the mid ocean ridge that is above sea level
(island)
o Younger ocean floor near the Mid-Ocean Ridge; less dense rock
o Older ocean floor near trenches; further away from mid ocean
ridge; more dense rock
EVIDENCE OF SEA-FLOOR SPREADING
Molten Material: Found in the middle of the Mid-Ocean Ridge. The newest molten
material pushes the old material away. Scientists have seen this lava erupting and they
call it pillow lava.
Drilling Samples: The newest molten material pushes the old material further away from
the MOR. Therefore, the newest molten rock is found closer to the mid-ocean ridge and
the older material is found farther away (moving toward trenches).
Magnetic Stripes: The rock of the ocean floor shows the direction of the magnetic force.
When the rock cools the iron in the rock leaves a magnetic memory. The ocean floor has
magnetic striping that show reversal of the magnetic field.