Dynamic+Crust


 * Dynamic Crust**

Theory of Continental Drift (Alfred Wegener 1915)



 a) Laurasia- North America, Europe, Asia b) Gondwanaland- Africa, South America, Antarctica, Austrailia, and India

__Evidence__ · Continents seem to fit together · Fossils of individual species can be found on many different continents which are not close together. (example: Lystrosaurus was located in Antarctica, South America, Africa, India · Deposits of certain rock and mineral types correlate among continents. · Appalachian Mountains found in Northeast of United States are similar in age and structure as mountains in Greenland and Scandinavia.

__Structure of the Earth__ · Pressure and temperature increase as you move toward the center of the earth · Crust- the outer layer of the earth a) continental crust- composed mainly of the granite, low in density b) oceanic crust- composed mainly of basalt, high in density · Lithosphere- crust and the uppermost solid part of the mantle · Asthenosphere- underlies the lithosphere, composed of partially molten rock · Moho- the layer of molten rock extending from the crust downward 2850 KM · Outer Core- between mantle and inner core, composed of iron and nickel (liquid)  · Inner Core- solid iron and nickel located at the center of the earth

__Plate Tectonics__ · Plate tectonics is the study f the information and movement of plates · plates are composed of lithosphere (continental= thick, oceanic= thin) 12 major and several minor plates

__Earthquakes__ · An earthquake is a shaking of earth's crust caused by the release of energy - Reasons why the occur a) eruption of volcano b) the collapse of a cavern c) the impact of a meteor d) sudden movement along a plate boundary caused by the release of stress

__Depth of Earthquakes__ · Focus- the point on a fault plane at which the first movement occurs · epicenter- the point on earth's surface directly above the focus

__Earthquake Waves__ · Three basic kind of waves 1) Primary Waves (P-Waves)- back and forth wave motion; can travel through any material; fastest 2) Secondary Wave (S-Waves)- side to side wave motion; can travel through solids but not through liquids or gases 3) Surface Waves (L-Waves)- form when P and S waves reach the surface which move slowly like ripples on a pond; slowest

__Locating an Earthquake__ · Seismograph- the instrument that detects and records earthquake waves · Seismogram- the sheet which display the zig- zag traces of earthquake waves  · P and S wave arrival time difference can then be used to determine the distance from the recording station to the epicenter
 * P-Waves always arrive before S-Waves**

__Locating the Epicenter__ - Triangulation -We then use the epicenter distance's from at least 3 recording stations to locate the epicenter - You need to next measure the distance to scale and drawing a circle from each station. Once 3 circles are drawn they will intersect at one common point. This location is the epicenter.

__Shadow Zone__ · The shadow zone is a wide belt around earth on the side opposite the focus of the earthquake. Seismic stations receive neither P nor S waves. · The cause of the shadow zone is the earths outer core. S-Waves cannot travel through the liquid core. While P-Waves are refracted (bent) in a smooth BC back to the surface.

__Convection Cells__

-Convection Cell- a circulatory motion in a liquid or gas transferring heat and energy that results from differences in density within the fluid. __Types of Tectonic Plates__ a) MID- Atlantic ridge- sea floor spreading at the mid ocean ridges recorded by the reversal of the magnetic poles in mineral grains
 * Plates move because of convection cells in the asthenosphere**
 * -Divergent Plate Boundary**
 * Place where two plates are moving away from each other
 * Paleomagnetism****-** the study of magnetism in ancient rocks
 * Polar Wandering-** as metallic mineral grains align themselves with their magnetic poles rock records show that the grains reverse the direction in which they point

__Collision__- when two plates carrying continents collide they push up usually causing mountains (Example: Himalayas) __Subduction__- when both plates do not contain continents, one of the plates is forced to sink under the other one. **
 * -Convergent Plate Boundary
 * When two plates move towards each other*

__Ocean-Continent__ - the ocean floor is more dense so it subdues to the continental causing offshore trenches, mountains or volcanoes (Example Western Coast of South America) __Ocean-Ocean__ - one plate will subdue to other one usually causing a deep trench (Example: Mariana's Trench)
 * The Plate Which Subdues is Composed of a More Dense Material**

When plates slide past one another usually causing a build up of pressure which is released in the form of an earthquake San Andrew Fault- many earthquakes are common along the fault where the north american plate is sliding past the pacific plate **Earthquakes and Volcanic Activity
 * Transform Plate Boundary
 * The Ring of Fire- a ring of earthquakes and volcanoes along the edge of the Pacific Ocean**

Felsic- magmas with relatively high silica are thick, light colored, and slow moving Mafic- relatively low silica content, thinner, darker, and flow more easily. - Magma contains dissolved gases that are given off as the magma erupts. The most important of these gases are water vapor, carbon dioxide, and sulfur. - Magmas containing large amounts of dissolved gases tend to produce more explosive eruptions. Lava- molten rock that has reached the surface Felsic Lava- thick and stiff called AA lava. Produce explosive eruptions. Mafic Lava- thin fluid called Pahoehoe lava. Lava pours out smoothly (less explosive)
 * Volcanism**
 * Magma- molten rock underground

**Lava Fragments Tephra- solid fragments of lava produced from explosive eruptions.

SMALL **ASH** . . **LAPILLI** . LARGE **BOMBS

Kinds of Eruptions Rift Eruptions- occur at long, narrow fractures in the crust such as mid- ocean spreading centers -When lava flows out smoothly and fluidly it forms a volcanic mountain with a broad base and gently sloping sides called a shield cone. Subduction Boundary Eruptions- are the result of thick magma that forms at subduction boundaries. -These eruptions are more explosive sue to the large amount of gases in the magma. -Forms a Cinder Cone with very steep sides. **Hot Spots - **Hot Spots are areas of volcanic activity in the MIDDLE of lithospheric plates. - Similar to the rift eruptions. Smooth flowing lava and shield cones.** Hot Spot stays in the same location as the lithospheric plate above it moves


 * Convergent Boundary Link- http://geology.com/nsta/convergent-plate-boundaries.shtml

Divergent Boundary Link- http://geology.com/nsta/divergent-plate-boundaries.shtml

Transform Boundary Link- http://geology.com/nsta/transform-plate-boundaries.shtml **