Transcript Slide 1
Earth is composed of 3 layers: 1. Core 2. Mantle 3. Crust 1. Core (inner & outer) – made of iron & nickel a. inner – super hot solid -about 4,000 mi. below surface of earth b. outer – super hot liquid -about 1,800 mi. below the surface of earth -temperatures can reach 8,000*F 2. Mantle -hot, dense mostly liquid rock -pockets of magma (rise & fall) -made of silicon, aluminum, iron, magnesium, and oxygen 3. Crust -rocky shell which forms earth’s surface -broken into more than a dozen slabs of rock called plates that rest on layer of the upper mantle -these plates carry earth’s oceans & continents -Continental Drift : theory that continents were once joined and then slowly drifted apart *super-continent was called Pangaea PANGAEA -Plate Tectonics – term scientists use to describe the activities of continental drift and magma flow which create many of Earth’s physical features *plates crash into each other, pull apart, or grind and slide past each other (about 4 inches or less per year) -Why do plates move? -convection currents *hotter material is less dense & rises (toward crust of Earth) *cooler material is more dense & sinks (toward core of Earth) *creates continuous circular motion/movement Why might a scientist want to study plate tectonics? Divergent Boundary -Plates move apart (rift) from each other (tension) 1. Continental-Continental = creates gap (rift valley) in which water can flow in *ex: Red Sea; Great Rift Valley 2. Oceanic-Oceanic = magma rises up & creates new crust on edges of the 2 plates -enlarges the ocean floor & forms underwater mountain ranges called ocean ridges *example: Mid-Atlantic Ridge – North American plate & Eurasian & African plates pulling apart Convergent Boundary In general: - Plates move toward each other & collide (compression) - One plate is forced below the other (subduction) 1. Oceanic-Continental -subduction occurs = heavier sea plate dives beneath lighter continental plate *sea plate begins to melt into magma pressure builds magma bursts thru crust to form volcanic mtns *ex: Andes Mountains in S. America – collision of Nazca and SA plates 2. OceanicOceanic -subduction occurs *sea plate begins to melt & magma rises to ocean surface in form of volcanic islands *example: Philippine islandscollision of Philippine & Pacific plates 3. ContinentalContinental -pressure builds until one plate is subducted *sometimes sinking plate melts & rises as volcanic mountains are formed *example: Himalaya mountains (South Asia) – collision of Indian & Eurasian plate Transform Boundary -Plates slide past each other along faults (cracks in the earth’s crust) - Crust is pulled and stretched (tension) until tension is released (Earthquake) -example: San Andreas Fault in California HOT SPOTS -Magma rises thru the tectonic plate -The magma erupts on the surface as lava & hardens to form volcanic islands -Magma continues to rise from the hot spot, building up an undersea volcano that will one day become an island -a chain is formed Animations Hot Spot Animation Guess the Tectonic Activity! Oceanic-Oceanic Convergent Oceanic-Oceanic Divergent Transform Continental-Continental Convergent Continental-Continental Divergent Oceanic-Continental Convergent