Plate Tectonics

Mrs. Anton

Continental Drift Caused By Plate Tectonics

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

Africa3. 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?• 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.

The Continents Today. Know Them

The Tectonic Plates – Know Them

Boundaries

• 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 Fold Mountains.Know where they are.

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 is younger closer to the rift valley • Sea floor is older 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 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)

New and Old Crust

QUESTIONS

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

• Answer: Mid-Ocean RidgeQuestion #2Where does magma pour out of on the sea floor?Answer:Rift ValleyQuestion #3:Where is the older sea floor, and where is the younger sea floor?

Answer: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

• First you need to know some vocab.Trench -long v-shaped valleythe deepest part of the ocean-Many at coast lines of continents

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

Evidence for Sea Floor Spreading

Evidence #1 – Disappearing CrustEarth 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

• 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