The Dynamic Crust

Earth’s Layers Terms Crust-the outermost layer of our planet varies from about 5 kilometers of thickness under the ocean to about 60 kilometers under some mountain ranges. Crust-the outermost layer of our planet varies from about 5 kilometers of thickness under the ocean to about 60 kilometers under some mountain ranges. Oceanic crust- under layers of marine sediment is composed of darker and Denser rock similar to basalt. Oceanic crust- under layers of marine sediment is composed of darker and Denser rock similar to basalt. Moho- thin layer or interface between the crust and mantle. Moho- thin layer or interface between the crust and mantle. Mantle- The layer below the Moho, it extends to a depth of about 2900 kilometers and includes most of the earth’s volume. Mantle- The layer below the Moho, it extends to a depth of about 2900 kilometers and includes most of the earth’s volume. Outer Core- It is thought to be liquid because S waves can’t go through it, composed of iron and nickel Outer Core- It is thought to be liquid because S waves can’t go through it, composed of iron and nickel Inner Core- Seems to be solid even though it is hotter than the outer core. Why Inner Core- Seems to be solid even though it is hotter than the outer core. Why Answer- The inner core has more pressure on it which keeps it solid.

Mantle/Crust Structure

Earth’s Structure

Convection Cells

Convection cells in the Mantle driving plate tectonics

A New Hope: Sea-floor Spreading

Today’s model:

Continental Drift

Theory of Continental Drift: The Crust is divided into plates, called Tectonic Plates The Crust is divided into plates, called Tectonic Plates The liquid of the mantle rises through the cracks between the plates and cools The liquid of the mantle rises through the cracks between the plates and cools Shifting of the plates causes Earthquakes, plates also buckle creating Mountains or Volcanoes Shifting of the plates causes Earthquakes, plates also buckle creating Mountains or Volcanoes

Evidence: Fossils

Evidence: Rock Sequences

Evidence: Glaciation

Evidence: Glaciation (cont’d)

“Problems with Continental Drift….

…an alternate explanation? 1928: Arthur Holmes suggested fluids rise toward the crust, spread, and sink again. 1930: Wegner dies, unable to adapt Holmes’ idea to his theory.

Testing the model….

Paleomagnetic reversals….

The seafloor spreading model is confirmed!

Magnetic variation animation o/flash/2_3.swf o/flash/2_3.swf o/flash/2_3.swf o/flash/2_3.swf

Convergent: Where compression forces push the earth’s plates together (where plates crash into each other)

1. Divergent: Where tension forces are pulling the earth’s plates apart. (where plates move away from each other)

Transform: Where shearing forces cause the earth’s plates to slide past each other. (where plates rub against each other in opposite directions)

We are going to fly over Alaska and the Aleutian Islands Aleutian Islands What features should we be looking for?

Unimak Island

Hot spot

SUMMARY OF P.T.: The plate tectonic model suggests: The plate tectonic model suggests: (1) continents can move across the surface of the globe (2) patterns of volcanism can change and shift across the globe as plates and their boundaries evolve and move (Ring of fire) (3) new oceans may grow (4) oceans basins close and are deformed to produce mountains

ANTICLINE  SYNCLINE  Folding

FAULTS Faults are CRACKS or FRACTURES in rocks caused by stress… Faults are CRACKS or FRACTURES in rocks caused by stress… They come in several varieties…. They come in several varieties….

SHEAR Shear stress is caused by side by side movement – example= TRANSFORM BOUNDARIES!

SHEAR (side-by-side) STRESS… can you think of an example?

This example of tension

This is a type of compression

NORMAL faults… FOOT WALL (‘STICKS’ OUT) HANGING WALL (‘HANGS’ ON)

REVERSE faults

STRIKE-SLIP faults (Transform)