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Transcript
Physical Science Review: Earth Science Earth’s Interior • The layers of the Earth are the crust, the mantle, and the core. • Crust- top layer, made up of solid rock Oceanic crust- beneath oceans, about 2.5-4.3 miles thick Continental crust- less dense but thicker than oceanic crust, about 12-25 mi. thick Abundance of Elements in Earth’s Crust • Mantle- layer of rock beneath the crust, about 1800 mi. thick. Makes up 80% of Earth’s volume. Outer mantle is solid, but inner mantle is hot and pliable. • Core- Composed mainly of iron and nickel. Inner core is solid metal, outer core is liquid metal. • Earth’s interior gets warmer with depth. Contains radioactive isotopes. Plate Tectonics • Continents may have at one time been one supercontinent called Pangaea. The mechanism by which the continents moved apart was continental drift. • Plate tectonics- theory that Earth’s surface is made up of large moving plates. Plate tectonics, cont. • Lithosphere- the thin outer shell of the Earth consisting of the crust and rigid upper mantle. • Beneath the lithosphere is the asthenosphere, consisting of slow-flowing molten rock. • Plates of the lithosphere “float” on top of the asthenosphere due to convection currents. Divergent Plate Boundaries • A divergent boundary occurs where two plates move apart, creating a gap. Magma rises from the asthenosphere and cools to form new lithospheric rock. • Rift valleys and mountain systems, such as midocean ridges, form at divergent plate boundaries. • The most studied mid-ocean ridge is the MidAtlantic Ridge, which extends from the Artic Ocean to the southern tip of South America. Convergent Plate Boundaries • Convergent plate boundaries are sites where oceanic plates slide beneath oceanic or continental plates and into the asthenosphere. • Ocean trenches, mountains, and volcanoes are formed at these subduction zones. • The deepest ocean trench is the Mariana Trench in the Pacific Ocean off the coast of Asia (6.8 mi. deep) Mountains • Mountains can form at the boundary between oceanic crust and continental crust. Oceanic plate melts, rising magma pushes up crust above it forming a mountain. • Example: Andes Mountains • Collision of continental plates also can form mountains. Example: Himalayas Transform fault boundaries • Fault- crack in the lithosphere where rocks move past one another. • Transform faults occur where plates move horizontally past each other at faults along plate boundaries. • Earthquakes often result from this plate movement. • Example: San Andreas fault Evidence for Plate Tectonics • The alignment of iron minerals in oceanic rocks supports the theory of plate tectonics. • Rocks at the center of a ridge are younger, and get older moving away from the ridge. • This suggests that the crust was moving away from the plate boundary. Earthquakes • Earthquakes result from sudden movement within the Earth’s lithosphere. As plates move, rocks along the edge experience immense pressure and break along a fault line. • Energy is released as vibrations or seismic waves. • Seismology is the study of earthquakes. • The Richter scale measures the magnitude of earthquakes Earthquakes, cont. • Focus- point where rocks first break, origin of the earthquake • Epicenter- point on Earth’s surface immediately above the focus. • Earthquakes generate three types of waves: 1) P waves (primary)- longitudinal waves, move fastest through rock 2) S waves (secondary)- transverse waves, move slower than p waves 3) Surface waves- move along Earth’s surface, cause the most destruction Volcanoes • Volcanoes are openings (vents) in Earth’s crust where magma has reached the surface. • Types of volcanoes: 1) Shield- gently sloping mountain formed by mild, frequent eruptions releasing fluid lava. Ex) Mauna Loa, HI 2) Composite- steep-sloped volcano made of alternating layers of ash, cinders, and lava Ex) Mt. Fuji, Japan 3) Cinder cone- smallest and most abundant, formed by violent eruptions releasing ash and lava. Active for a short time, then dormant Ex) Paricutin, Mexico Volcanoes, cont. • Volcanoes forming underwater are called seamounts. • Volcanoes occur at convergent plate boundaries. 75% of active volcanoes are located along the edge of the Pacific Ocean where oceanic plates collide with continental plates. “Ring of Fire” • Volcanoes can also form at divergent plate boundaries. When plates diverge, magma fills the gap and creates volcanic mountains. Ex) Iceland on the Mid-Atlantic ridge is a volcanic island Minerals and Rocks • Minerals are nonliving substances found in the Earth that have a definite chemical composition and structure. • Rocks are made up of minerals. • The three categories of rocks include: Igneous, Sedimentary, and Metamorphic. • Rocks are continually broken down and reformed by a process called the Rock Cycle. Types of Rocks • Igneous- rock formed from cooled and hardened magma (lava). 1)Extrinisic- cools on Earth’s surface ex) obsidian 2)Intrinsic- cools beneath Earth’s surface ex) granite • Sedimentary- formed from compressed deposits of sediments Ex) sandstone • Metamorphic- formed from other rocks as a result of heat, pressure, or chemical processes. Ex) marble How Old Are Rocks? • Principle of Superposition- Assuming no change in the position of rock layers, the oldest will be on the bottom and the youngest on top. Gives relative age of rocks. • Radioactive dating can give the absolute age of rocks. Weathering of Rocks • Physical weathering breaks down rocks by water erosion, ice wedging, plant root wedging, wind abrasion, and other physical forces. • Chemical weathering occurs when minerals in the rock react chemically and break down, such as in the presence of acid rain. The Atmosphere • The atmosphere is a layer of gases surrounding the Earth. • The main gases in the atmosphere are nitrogen (78%) and oxygen (21%) and other gases in trace amounts. • The atmosphere shields living things from harmful UV radiation, and helps maintain surface temperatures suitable for life. Layers of the Atmosphere • Troposphere- dense layer closest to Earth’s surface where weather occurs, temp. decreases with altitude • Stratosphere- contains the ozone layer which protects against UV rays, temp. increases with altitude. • Mesosphere- coldest layer • Thermosphere- temp. increases with altitude Changes in Earth’s Atmosphere • Photosynthetic organisms add O2 to the atmosphere. • Animals release CO2 into the atmosphere through cellular respiration. • Burning fossil fuels releases large amounts of carbon dioxide, which may lead to global warming. • Manmade chemical released into the air are depleting the ozone layer. Greenhouse Effect • The greenhouse effect keeps the Earth warm. • Greenhouse gases such as water vapor and carbon dioxide absorb energy from the sun, which warms the troposphere. • Global warming results when too much heat is trapped, which could cause polar ice caps to melt, ocean levels to rise, and droughts to occur in some places. Water • Water is continually moved through the troposphere by the water cycle. • Water from oceans and lakes evaporates and rises in the atmosphere. After it cools and condenses, the water falls back to Earth as precipitation. • Humidity is the amount of water vapor in the atmosphere. • Warm air can hold more moisture than cooler air. • Clouds form as warm, moist air rises. • Clouds are classified according to their appearance and the altitude at which they occur. Wind • Wind is caused by differences in air pressure. • The air in a pressure gradient moves from areas of high pressure to areas of low pressure. • Earth’s rotation affects the direction of winds. This is the Coriolis effect. • Winds in the Northern Hemisphere curve right, while winds in the Southern Hemisphere curve left. Weather and Climate • Weather refers to the atmospheric conditions at a certain location at a given time. • Climate refers to weather patterns occurring over an extended period of time. • Climate is influenced by latitude, topography (landforms), air circulation, and ocean currents. • Coastal areas tend to have warmer climates than inland areas due to warm ocean air. • A warm front forms as a warm air mass moves over a slower cold air mass. • A cold front forms as a cold air mass moves under a slower warm air mass. • Tornadoes are high-speed rotating winds that form as air begins to rotate around quickly rising warm air. • Hurricanes are large storm systems that are characterized by high-speed winds and very low pressures. Seasons • Earth’s tilt on its axis as it revolves around the Sun causes the seasons. • Summer occurs in the Northern Hemisphere when the North Pole is tilted toward the Sun. • The summer solstice is the longest day of the year, around June 21. • When the North Pole is tilted away from the Sun, it is winter. • The winter solstice, the day with the shortest period of daylight, occurs around December 21. • The spring equinox (Mar. 21) and autumn equinox (Sept. 22) are days when daylight and dark are equal. The Seasons