#1 Exam Scientific Explanations are tentative, based on empirical obs., predictable and testable, and provide well defined natural cause to explain occ. Of natual event. Stars and Planets: stars use hydrogen as fuel. High temps. Stars fuse hydrogen atoms together=nuclear fusion and forms helium. When hydrogen is used up stars burn out. Violently=supernovas, Less violent=Sun, ends at carbon. When stars form, surrounded by disc of cosmic debris. Gravity pulls debris together=Planets. Heavy planets=close to star. Light planets=far from star. Stars and Planets form at SAME time. Big Bang=formation of universe, not solar system. Big Bang created hydrogen and helium. Hydrogen= 1 proton + 1 electron. Helium=2 protons+2 neutrons+2 electrons. 75% of universe is hydrogen/ 25% helium. Stars vary in size and age. Solar System: 8 planets, 4 Terrestrial=crust, mantle, core in layers=Mercury, Venus, Earth, Mars. 4 Jovial=large gas, with many moons and rings=Jupiter, Saturn, Neptune, Uranus. Earth, Sun and Seasons: season temp. changes due to tilt in earths axis and angle from sun rays. Tilt=23.5 degrees. Tropic of cancer and Capricorn are 23.5 N. and S. of equator. Wegener's Hypothesis: proposed continental drift hypothesis=continents came together to form Pangea, then split apart individual continents 200 MYA. Drifted to current pos. He made 3 observations: Matching Features-plant and animal fossils matched between continents, continuous mountain belt form if Pangea reassembled. Fit of Continents-fit together by the continental shelf. And unusual rock sequence between Africa and S. America. Paleoclimate (past climates)- thick ice sheet, glacial rocks in tropical condition. Hypothesis not accepted b/c he couldn't explain HOW continents moved and supporters of prior contracting theory had alt. explanations. Earthquake locations were NOT used to supp. Wegeners hypothesis. Evidence from Seafloor: Seafloor Topography-Continental Shelf-narrow, shallow, ocean surrounding continents (Bahamas) It gradually flattens out to form Abyssal Plains-level, often has volcanos (Bermuda islands) Going away from continents, abyssal plain go into Oceanic Ridge System-underwater mtn. belt and source of volcanic activity. Divided into 4 sections; Mid-Atlantic ridge, E. Pacific rise, Antartic ridge, and Indian Ridge. Occupy most seafloor in all ocean basins. Heat flow is greatest=hot magma erupting onto seafloor. (Ring of Fire) Oceanic Trenches-along margins of some continents or adjacent to volcanic island chains. Most common in Pacific. Earthquakes Narrow/Deepest. get deeper AWAY from trenches, Ridges are located near CENTERS of ocean basins, Trenches near MARGINS. Age of Ocean Floor-ocean crust is young compare to continents. Oldest oceanic rocks less than 200 MY old. Oldest rocks on Cont. Crust are 4 BY old. Age of ocean floor is YOUNGEST @ oceanic ridges, and OLDEST @ edges of ocean. Seafloor Spreading Hypothesis-new ocean floor is continuously forming along ridge system by magma rising from below, so existing rocks move away from ridge. Paleomagnetism-magnetic record stored in rocks. Eartths magnetic field varies w/ loc. And can be defined by its direction and inclination. Mag. Field is inclined down in N. Hem. And Up in S. Hem. Inclination increases between equator and poles. Mag. Field reversals-postive and negative mag. Poles have switched positions in the past. Plate Tectonics-8 plates; African ,Antartic, Eurasion, Indian-Australia, Nazca, N. American, Pacific, S. American. Most plates composed of BOTH continental and oceanic lithosphere. Lithosphere divided into mobile tectonic plates. Lithosphere=crust & upper mantle. Outermost layer of earth. Asthenoshpere=inner layer, located in mantle, solid rocks. Plate tectonic Cycle-oceanic lithosphere is created by magma rising from the asthenosphere at the ocean ridge, plates move away from ridge and may be consumed as they descend into mantle at subduction zone. Plate movements occur slowly. Transformslabs of lithosphere slide past one another (San Andreas Fault) Convergent-plates move toward eachother, oceanic lithosphere consumed at subduction. Divergent-plates move apart, new lithosphere is created, forms rift valley. Narrow=youth, wide=old. Rocks Melt- 1.) Increase in pressure, temp increases w/ depth but increase press. Impedes melting. Proximity of magma raises temp. 2.) Decreasing Pressuredecompression melting occurs as rocks rise toward surface (below oceanic ridges) 3.) Addition of waterchemical reactions in presence of water lower temp. necessary for melting minerals. Generation of Earthquakes and volcanoes: older oceanic lithosphere is destroyed at subduction zone to balance formation of new material. Chem. Reactions in descending plates release water, which lowers melting pointof minerals in mantle to cause melting and generate magma, to create volcanoes. Faults, Earthquakes and Plate Tectonics: Fault-fracture in crust on which movement has occurred. Zone of weakness where earthquakes occur. Focus-location where movement begins. Epicenter-location on