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!