Dynamic+Crust

Science Notes 1-11-10

** (alfred wegener 1915)
 * THEORY OF CONTINENTAL DRIFT:

__**Pangea**__- A large landmass containing all of the continents. Which eventually broke into two land masses. Gondwanalando Africa, South America, Antarctica, Australia, India.
 * __Laurasia__**- North America, Europe, Asia.

Continents seem to fit together. Fossils of individual species can be found on many different continents which are not close together. (//ex. Lystrosaurus was located in Antarctica, South America, Africa, India.//) Deposits of certain rock and mineral types correlate among continents. Appalachian mountains found in north east of u.s. are similar in age and structure as mountains in greenland and scandinavia.
 * EVIDENCE: **

Pressure and temperature increase as you move toward the center of the earth. __Crust__- the outer most layer of the earth. __Lithosphere__- crust and uppermost solid part of the mantle. __Asthenosphere__- underlies the lithosphere, composed of partially molten rock. __Moho__- the boundary between the crust and the mantle. __Mantle__- the layer of molten rock extending from the crust downward 2850 KM. __Outer core__- between mantle and inner core, composed of iron and nickel. __Inner core__- solid iron and nickel located at the center of the earth.
 * STRUCTURE OF THE EARTH**
 * a)** Continental Crust- composed mainly of granite, low in density.
 * b)** Oceanic Crust- composed mainly of basalt, high in density.

HERE IS A SIMPLE DIAGRAM OF THE LAYERS OF THE EARTH, BELOW:


 * **THE OUTER CORE IS ACTUALLY LIQUID !**

PLATE TECTONICS ** -Plate tectonics is the study of **formation** and **movement** of plates. -Plates are composed of lithosphere //(continental= thick, oceanic= thin)// 12 major and several minor plates.

- An earthquake is a shaking of Earth's crust which is caused by the release of energy. The reason why they occur is because of the collapse of a cavern, eruption of a volcano, and impact of a meteor, sudden movement along a plate boundary caused by the release of stress.
 * 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. - They have specific patterns where earth quakes seem to occur.
 * DEPTH OF EARTHQUAKES **

- three basic kinds of waves. __P-waves__ (primary) - back and forth wave motion: can travel through any material; fastest. __S-waves__ (secondary) - side to side wave motion; can travel through solids but not through liquids or gases. __L-waves__ (surface) - form when P and S waves reach the surface which move slowly like ripples on a pond; slowest.
 * EARTHQUAKE WAVES **

__seismograph__- the instrument that detects and records earthquake waves. __seismogram__- the sheet which displays the zig-zag trace 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. triangulation You need //at least// **3 locations** to find the epicenter.
 * LOCATING AN EARTHQUAKE **
 * P-WAVES ALWAYS ARRIVE BEFORE S-WAVES!!> i guess if you wanted to remember with a "trick" P comes before S in the alphabet, and P waves arrive first.**

__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.
 * LOCATING AN EPICENTER**

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 earth's outer core. S- waves can not travel through the liquid outer core. While P waves are refracted (bent) in a smooth arc back to the surface.
 * SHADOW ZONE**

A circulatory motion in a liquid or gas transferring heat energy that results from differences in density within the fluid.
 * CONVECTION CELL:**

__divergent plate boundary__- place where two plates are moving apart from each other. to pull apart. a.) __mid- atlantic ridge__- sea floor spreading at the mid ocean ridges recorded by the reversal of the magnetic poles in mineral grains.
 * TYPES OF PLATE BOUNDARIES**:

DIVERGENT: - two plates are shifting apart, or to be pulled apart.

__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.


 * CONVERGENT PLATE BOUNDARY:**

-when two plates slide into one another __COLLISION__- WHEN TWO PLATES CARRYING CONTINENTS COLLIDE THEY PUSH USUALLY CAUSING MOUNTAINS. (//EX. HIMALAYAS//) __SUBDUCTION__- WHEN BOTH PLATES DO NOT CONTAIN CONTINENTS, ONE OF THE PLATES IS FORCED TO SINK UNDER THE OTHER ONE.
 * When two plates move toward each other.

THE PLATE WHICH SUBDUES IS COMPOSED OF A MORE DENSE MATERIAL.... __OCEANIC CONTINENT__- the ocean floor is more dense so it subdues to the continental causing offshore trenches, mountains or volcanoes. (//ex.// //western coast of south america. )//** __OCEAN-OCEAN__ **- one plate will subdue to the other one usually causing a deep trench (//EX. Mariana's trench//)**

San Andrea's fault- many earthquakes are common along the fault where the north american plate is sliding past the pacific plate.**
 * TRANSFORM PLATE BOUNDARY.....**
 * - When plates slide past one another usually causing a built up of pressure which is released in the form of an earthquake.

__The Ring of Fire-__ Edges of the Pacific Ocean.
 * EARTHQUAKE AND VOLCANIC ACTIVITY**

__Magma__ - molten rock underground. __Felsic__ - magmas with relatively high silica are thick, light colored, and slow moving. __Mafic__ - r elatively low silica content, thinner, darker, and flow more easily.
 * Volcanism****:

-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 eruption.

__Lava__ - molten rock that has reached the surface. __Felsic Lava__ - thick and stiff called __AA__ lava, Produce explosive eruptions __Mafic Lava__ -** thin and fluid called //Pahoehoe//** lava. Lava pours out smoothly. (less explosive.) **

LAVA FRAGMENTS below is an example:
 * __Tephra__ - solid fragments of lava produced from explosive eruption.**

KINDS OF ERUPTION two plates pull apart, magma comes up, flows out. - when lava flows out smoothly and fluidly it forms a volcanic mountain with a broad base and gently sloping sides called a //shield cone.
 * // __rift eruptions__ //- occur at long, narrow fractures in the crust such as mid- ocean spreading centers.

__Subduction boundary eruptions__- are the result of thick magma that forms at subduction boundaries. - these eruptions are more explosive due to the large amount of gases in the magma.

Forms a cinder cone with very steep sides: //** - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

//H O T S P O T S - Similar to rift eruptions. smooth flowing lava and shield cones. THE HOT SPOT STAYS IN THE SAME LOCATION AS THE LITHOSPHERIC PLATE ABOVE IT MOVES **//
 * -Hot spots are areas of volcanic activity in the __MIDDLE__ of the lithospheric plates.