Dynamic Earth Notes

Final Review

Theories of crustal movement

1.       Wegener- Continental drift-

 At one time all the continents were together in a giant continent called Pangaea.

Over time they have moved apart to where they are today.

Evidence-

1.    Continents appear to fit together like puzzle pieces.

2.    Fossils and rock types match up along edges of continents where they fit.

3.    Mountain ranges match up.

4.    Fossils of warm weather plants found in Antartica and glacial evidence found by equator.

Problems- No idea what caused this only that it did happen.

Not believed by other scientists.

2.       J Tuzo Wilson-Plate tectonics and Sea floor speading

Modified Wegener’s theory with reason behind movement of plates.

Plates move due to density differences in the earth’s mantle.  Hot molten material rises up toward surface because it is less dense, and colder, more dense material sinks down toward center of the earth.  This is called convection currents or convection cells.

Explains- way plates move at boundaries

1.       Convergent continental plates- 2 continental plates come together and form mountains where they collide.

2.       Transform plates- 2 plates slide past each other like at San Andreas fault in California.

3.       Divergent oceanic plates- 2 oceqn plates separate at mid-ocean ridge forming new crust and under water mountain chain.

4.       Convergent oceanic and continental plates- one oceanic runs into continental plate forming trench where is subducted or forced beneath it.

-Sea floor spreading

Sea floor moves apart at divergent boundaries

Evidence-

1.    younger rock found at ridge while oldest rock found nearer continent

2.    can match up when rock is formed at ridge on either side by looking at the way magnetic crystals in rocks line up

if the magnetic particles are facing toward magnetic north where it is today, they were formed when magnetic north was at geographic north

if they are facing toward geographic south, the rock must have been formed when magnetic north was at the south pole.

( this also shows that the earth’s magnetic poles have changed position over time)

3.    Can match up ages on either side of ridge in stripes from youngest to oldest

4.    pillow rocks, type of igneous rock are found running along the ridge- formed from molten material cooling rapidly under water

How we prove plates move today

1.       Satellites- monitor movement of  plates by following sensors in the ground.