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Geo 2 EQ: How do we describe Earth’s position, and how do processes shape the earth How do we know anything about the Earth • • • • • • Interior structure Volcanoes and hotspots Earthquakes Tectonic plates Tectonic motion Reconstruction of the Earth’s history Interior Based on Composition • Crust – solid, relatively low density silicate rock • Mantle – Semi fluid, denser (iron and magnesium bearing) rocks • Core – Liquid then solid iron and nickel with traces of heavier elements Based on Motion • It turns out that the upper section of the mantle is adhered (stuck to the underside side of the crust to form what we call tectonic plates Volcanoes Volcanoes • Volcanoes are the result of hot spots within the crust or mantle of the earth. • The hot, liquid rock will break through weak spots in the surface and form volcanoes or flood basalts. • Many volcanoes do not release lava, instead they spit ash and small bits of lava called lapilli. • Some eruptions are quiet with very fluid (low viscosity) lava flows while others are explosive Volcanoes Quiet lava flows Volcanoes Mt. St. Helens before the explosive eruption Volcanoes Time lapse of the eruption Volcanoes Mt. St. Helens after the eruption Volcano locations Earthquakes Earthquakes • Earthquakes are a result of motion within the earth. • This only occurs where the earth is solid and therefore can only occur within about 100 miles of the surface • Earthquakes provide the best evidence regarding the interior structure of the Earth. Earthquakes Earthquakes Earthquakes Earthquakes Tidal waves or Tsunamis result when a large section of the sea floor suddenly moves and therefore displaces a massive amount of water. Earthquakes Earthquakes by depth. Notice that the deep earthquakes occur only at subduction zones. Tectonic Plates Types of Plate Tectonics Subduction: a heavier sea plate dives beneath a lighter continental plate. Accretion: pieces of the Earth’s crust come together slowly as the sea plate slides under the continental plate. Spreading: sea plates pulling apart Types of Plate Tectonics Subduction: Causes violent earthquakes and volcanic eruptions to form new land. Accretion: less violent pushes land up under ocean near shore line expand land outward. Spreading: Creates underwater volcanic eruptions that create new land between sea plates. Subduction Accretion Spreading Plates Spreading Faults - cracks in the Earth’s crust San Andreas Fault Tectonic Plates Our first evidence of tectonic motion is based on similar fossils and rock types on opposing sides of the ocean Tectonic Plates Pacific Ring of Fire Most volcanoes and earthquakes on Earth. Pangea • What is Pangaea? • Pangaea was a super continent at one time. • Scientists use the similarity of rock types and fossil types that date to the same age to support their theory that the continents were connected to form a super continent. • The map below give just one example of areas on different continents that show the same fossils and rock types. Pangea Pangea The break up of Pangea Where are we going? We appear to be headed for another super continent as North America, South America, Asia and Australia converge in the ever shrinking Pacific Ocean The Hydrosphere • About 70% of the earth’s surface! • Factor for settlement. The Water Cycle • Run and get a glass of water and put it on the table next to you. Take a good long look at the water. Now -- can you guess how old it is? • The water in your glass may have fallen from the sky as rain just last week, but the water itself has been around pretty much as long as the earth has! The Water Cycle Evaporation • The water cycle has no starting point. But, we'll begin in the oceans, since that is where most of Earth's water exists. The sun, which drives the water cycle, heats water in the oceans. Some of it evaporates as vapor into the air. Transpiration • Water transpired from plants and evaporated from the soil. Do plants sweat? Condensation • Water vapor in the air gets cold and changes back into liquid, forming clouds. This is called condensation. • Air currents move clouds around the globe • You can see the same sort of thing at home... pour a glass of cold water on a hot day and watch what happens. Water forms on the outside of the glass. That water didn't somehow leak through the glass! It actually came from the air. Water vapor in the warm air, turns back into liquid when it touches the cold glass. Precipitation • Precipitation occurs when so much water has condensed that the air cannot hold it anymore. The clouds get heavy and water falls back to the earth in the form of rain, hail, sleet or snow. Collection • When water falls back to earth as precipitation, it may fall back in the oceans, lakes or rivers or it may end up on land. When it ends up on land, it will either soak into the earth and become part of the “ground water” (infiltration). Some water infiltrates deep into the ground and replenishes aquifers (saturated subsurface rock), which store huge amounts of freshwater for long periods of time. Some infiltration stays close to the land surface and can seep back into surface-water bodies and some ground water finds openings in the land surface and emerges as freshwater springs. Over time, though, all of this water keeps moving, some to reenter the ocean, where the water cycle "ends" ... oops - I mean, where it "begins." Bodies of Salt Water • Oceans About 97 percent of the hydrosphere is a huge body of salt water divided into five oceans: the Atlantic, the Pacific, the Indian, Southern and the Arctic Oceans. • Seas, Gulfs, and Bays Large bodies of salt water partially enclosed by land comprise seas, gulfs, and bays How can we use this water? Desalination: converts ocean water into drinking water Why aren’t we all doing this? Climate vs. Weather Climate is often confused with weather… Weather is the condition of the atmosphere in one place during a limited period of time Climate is the term for the weather patterns that an area typically experiences over a long period of time. Climate vs. Weather con’t… • Example of WEATHER : When you look out the window or watch the news to see if you need an umbrella today. • Example of CLIMATE: People who live in Seattle frequently use umbrellas because of the rainy, wet climate. Climate vs. Weather con’t… The climate & weather in a particular region is determined by many factors…the most important of which is the earth’s position in relation to the sun. Earth’s Tilt & Rotation The Earth’s tilt is one reason for variations in sunlight. It is tilted at an angle, 23 ½ degrees, on an imaginary pole that runs from the North Pole to the South Pole. Tilt & Rotation Con’t… • Because of the tilt of this axis, not all places on the planet receive the same amount of direct sunlight at the same time. • For this reason, the angle of tilt affects the TEMPERATURE…areas that receive a large amount of direct sunlight have warmer temps than places that receive little sunlight. ROTATION The Earth rotates on it axis, making 1 complete rotation every 24 hours. It rotates from WEST to EAST. This is how we get day & night! REVOLUTION • While the planet is rotating on its axis, it is also REVOLVING around the sun. • It takes about 365 days to complete one trip around the sun. • The Earth revolves counterclockwise around the sun. • “About” refers to leap year, Feb. 29th, every four years, as a result of 365 ¼ days. Seasons • The earth’s tilt & it’s revolution cause changes in the angle and amount of sunlight that reach different locations on the planet. • This results in the seasons. SEASONS • Fall – September 22 • Winter – December 22 • Spring – March 21 • Summer – June 21 SOLSTICE • At 2 moments during the year the earth’s poles point toward or away from the sun more than at any other time. • Definition: The time that the earth’s poles point at their greatest angle toward or away from the sun is called a solstice. SOLSTICE con’t… • Solstices occur around Dec. 21 & June 21. • In the N. hemisphere, the day in Dec. on which the solstice occurs is the shortest day of the year and is the first day of winter. • The day in June on which the solstice occurs is the longest day of the year and is the first day of summer. EQUINOX • Definition: An equinox, which means equal night in Latin, occurs twice a year when the earth’s poles are not pointed toward or away from the sun. EQUINOX con’t • Both hemispheres receive an equal amount of sunlight-exactly 12 hours. • If you were to travel anywhere in the world during an equinox, daylight and darkness would last the same amount of time. • Equinoxes occur around March 21 & Sept. 22 • The March equinox signals the beginning of Spring & theSept. one signals the beginning of fall. POLES • The amount of sunlight at the Poles varies most dramatically as the earth’s revolution and tilt cause the changing seasons. • For 6 months of the year, one Pole is tilted toward the sun and receives continuous sunlight, while the other Pole it tilted away from the sun and receives little to no sunlight. POLES con’t… • At the North pole, the sun never sets from about March 20-Sept. 23. • It Is vice versa for the south pole. • It switches 6 months later for each location! This powerpoint was kindly donated to www.worldofteaching.com http://www.worldofteaching.com is home to over a thousand powerpoints submitted by teachers. 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