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Chapter 2 Lesson 1

 Textbook pages 50-59

EARTH·S

STRUCTURE

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Core

Crust

LithosphereMantle

Plate tectonics

Plate boundaries

 WORDS TO KNOW

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Earth is made up of several layers of rock and metals.

� Crust: thinnest layer, almost all solidrock 

� Mantle: solid rock just below the crust,more than 2/3 of the Earth·s mass

� Lithosphere: rigid (hard) shell formed where the mantle and the crust meet

� Core: inside layer, divided into twolayers.

� Outer core: the only liquid layer, mostly molten(melted) iron and nickel, with some sulfur andoxygen

� Inner core: hotter than the outer core, but solidbecause of the high pressure

EARTH·S LAYERS

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 Alfred Wegener

German meteorologist and geologist

�

In 1915, he said that continents weremoving across Earth·s surface.

� E vidence: same kind of fossils foundon opposite sides of an ocean or onthe edges of different continents

�

He couldn·t explain how thecontinents moved, since the crust wassolid, so most scientists of his timebelieved he was wrong.

CONTINENTAL DRIFT THEORY 

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In the 1950·s, scientists discoveredmolten (melted) rock from themantle was rising to the Earth·s

surface in the ocean basins. They began to believe that thelithosphere might be made of giantpieces of rock, called  plates, that´floatµ on top of the mantle,slowly moving across the Earth·s

surface. This theory is known as plate tectonics.

� Oceanic plates: made of ocean-floor material

� Continental plates: lighter rock ´ridingµ on top of the dense

rock 

PLATE TECTONICS

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 A boundary is where two plates meet.

 A. Diverging Boundaries: The two

plates are moving away from eachother. Molten rock rises to fill thegap, which makes new crust as itcomes to the surface.

B. Converging Boundaries: The twoplates are pushed together.

Sometimes one plate will move underthe other one.

C. Sliding Boundaries: The two platesslide past each other, moving inopposite directions. These aresometimes called transform

boundaries.

 TY PESOF PLATE BOUNDARIES