Plate Tectonics
Seafloor Spreading
Plate Tectonics
4 – Name the four main layers of the earth from inside to outer most layer.
3 – Name the three physical structures of the Earth.
2 – Identify the state of matter for the two parts of the core.
1 – Write one fact about the Earth’s layers you find interesting.
When you are finished with Bellringer finish reading section 6.2 the rest of page 192 to page 195.
Bellringer
-Inner Core-Outer Core-Mantle-Crust
L-LithosphereA-AstenosphereM-MesosphereInner Core is SOLIDOuter Core is HOT MOLTEN LIQUID
I think it is interesting how the outer core spins around the inner core. What about you?
Plate Tectonics
Mid-Ocean Ridges • Mid-ocean ridge – undersea mountain chain
where new ocean floor is produced– Discovered by using sonar (a device that
bounces sound waves off underwater objects and then records the echoes)
• Harry Hess – (American) first geologists to study mid-ocean ridges– Found evidence to back up
Wegener’s Continental Drift Theory– Called this seafloor spreading
- Sea-Floor Spreading
Plate Tectonics
Mid-Ocean Ridges• The East
Pacific Rise is just one of the many mid-ocean ridges that wind beneath Earth’s oceans.
- Sea-Floor Spreading
Plate Tectonics
What Is Sea-Floor Spreading?• Sea-floor spreading –
The sea floor spreads apart along both sides of a mid-ocean ridge as new crust is added– Ocean floors move
like conveyor belts, carrying the continents along with them.
- Sea-Floor Spreading
Plate Tectonics
Evidence for Sea-Floor Spreading• Hess found evidence to support his theory of sea-
floor spreading, which included: – eruptions of molten material, magnetic stripes in
the rock of the ocean floor, and the ages of the rocks themselves.
- Sea-Floor Spreading
Plate Tectonics
Evidence for Sea-Floor Spreading• Evidence From Molten Material
– 1960’s – submarine Alvin found rocks along the ocean floor running parallel with the ridge
– These type of rocks only form when molten material hardens quickly after erupting under water
• Evidence From Magnetic Stripes – rock that makes up the ocean floor lies in
a pattern of magnetized “stripes.” – record of reversals in Earth’s magnetic
field.
- Sea-Floor Spreading
Plate Tectonics
Evidence for Sea-Floor Spreading• Evidence From Drilling Samples
– Glomar Challenger – (1968) drilling ship that obtained rock samples from the ocean crust
– Found that the rocks closest to the mid-ocean ridge were “younger.”
– The farther away from a ridge the samples were taken, the older the rocks were
Plate Tectonics
Subduction at Trenches• Deep-ocean trench – deep
valley along the ocean floor beneath which oceanic crust slowly sinks toward the mantle.– The oceanic crust bends
downward into the mantle• Subduction – process by
which oceanic crust sinks beneath a deep-ocean trench and back into the mantle. – Occurs at a convergent plate
boundary
Trench
Subduction
Plate Tectonics
Subduction at Trenches• In a process taking tens of millions of years, part
of the ocean floor sinks back into the mantle through deep-ocean trenches.
- Sea-Floor Spreading
Plate Tectonics
Growing an Ocean• Because of sea-
floor spreading, the distance between Europe and North America is increasing by a few centimeters per year.
- Sea-Floor Spreading
Plate Tectonics
Complete 6.2 Review on the answer sheet provided to you.
-Key Concepts: #’s 1-3-Critical Thinking: #’s 4-5
-Challenge: # 6YES YOU HAVE TO DO THE
CHALLENGE!!!!Also, complete the reverse side of
the answer sheet. Turn In!