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Plate Tectonics. Mrs. Anton. Continental Drift Caused By Plate Tectonics. Continental Drift. C ontinents once one large landmass - Pangea Broke and moved apart into 7 continents Alfred Wegener Proof – there are three 1 . Fossil E vidence – Mesosaurus found on Africa and S. America.

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Plate tectonics

Plate Tectonics

Mrs. Anton

Continental drift
Continental Drift

  • Continents once one large landmass - Pangea

  • Broke and moved apart into 7 continents

  • Alfred Wegener

  • Proof – there are three

    • 1. Fossil Evidence –

      • Mesosaurus found on Africa and S. America.

      • Mesosaurus can’t live in salty water. How did it swim across the salty Atlantic?

      • Continued ………………..

More proof of drift

  • 2. Coastline Evidence

    • Continents seemed to fit like puzzle – S. America and Africa

      3. Mountain Ranges Evidence –

    • Ages and kinds of rocks seem to be the same

    • Like one long chain

    • Mountain Chain along eastern US and Canada similar to Greenland and Europe

    • Famous fold mountain ranges – Andes (S. America), Rockies(N. American), Alps (Eurasia), Himalyas(Eurasia)

Why continents are drifting
Why Continents are Drifting?

  • Plates located on lower part of mantle - flows on a thick liquid. Like life rafts on a lake

  • Two types plates – oceanic (more dense) and continental

  • So oceanic subducts under continental plates

  • Plates move the continents and oceans a few centimeters each year.

  • Convection Currents move the plates

  • Convection Currents – hot mantle rock rises, while cool rock sinks, causing plates to move.

    Think of an egg on the surface of boiling water.

    Egg moves as convection currents move the water.


  • Divergent – When two plates move apart

  • Convergent – when two plates move together

  • Fold mountains are caused when two plates move together and squeeze the land above them. Causes a wrinkle or fold.

  • Fold Mountains – Andes, Rockies, Alps, Himalayas

4 f old m ountains know where they are
4 Fold Mountains.Know where they are.

Sea floor spreading
Sea Floor Spreading

  • Process that forms new sea floor

  • Two kinds of crust – oceanic and continental

  • Oceanic is heavier (more dense) – made of basalt rock

  • Theory by Harry Hess

  • Mid- Ocean Ridges – mountain ranges under the ocean. Mid-Atlantic Ridge is an example

  • Proof of spreading – Rift Valley -a deep crack with magma found running down center of Mid- ocean ridge

  • Sea floor isyounger closer to the rift valley

  • Sea floor isolder further away by the coasts of the continents

    When it shows above the water, it’s an island

    • Example – Iceland ( a mountain peak on the Mid-Atlantic Ridge

Sea floor spreading1
Sea Floor Spreading

When a mid ocean ridge (ocean mountain) shows above the water, it’s an island

  • Example – Iceland ( a mountain peak on the Mid-Atlantic Ridge)


What is the term used for the chain of mountains on the sea floor?

Plate tectonics

  • Answer: Mid-Ocean Ridge

    Question #2

    Where does magma pour out of on the sea floor?


    Rift Valley

    Question #3:

    Where is the older sea floor, and where is the younger sea floor?


    The older sea floor is closer to the continents and the younger sea floor is close to the rift valley (middle of ocean).

Vocab for sea floor spreading
Vocab for Sea Floor Spreading

  • First you need to know some vocab.


    -long v-shaped valley

    the deepest part of the


    -Many at coast lines of


    Subduction Zone – Place where old crust is pushed down into a trench

Evidence for sea floor spreading
Evidence for Sea Floor Spreading

Evidence #1 – Disappearing Crust

Earth is 4.5 billion years old BUT the oldest rocks on sea floor is only 175 million years old

  • Where has the old sea floor gone?

    It is believed – old sea floor has subducted into the trenches, down into the mantle.

    What would happen to the Earth if the sea floor didn’t subduct into the trenches?

What to study
What To Study

  • Study this powerpoint

  • Your own notes – you may have added some hints

  • Your own illustrations of continental drift and the illustrations you took during the centers