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Transcript
Earth Astronomy 311 Professor Lee Carkner Lecture 12 Terra -- The Earth Goddess Earth Facts Size: 12700 km diameter Orbit: Description: Earth’s Celestial Motions Earth is tilted on its axis by 23 1/2 degrees Earth has large satellite, The Moon May stabilize tilt of axis Earth’s Atmosphere Composition: Very different from other atmospheres Early Atmosphere Where did the original atmosphere come from? Early composition: Formation of Atmosphere Start with CO2, H2O, CH4, NH3 C, H, O form H2O, CO2 Final atmosphere -- O2 and N2 Earth’s Atmosphere Atmosphere and Temperature Planets with no atmosphere have a temperature determined by radiation balance: For a steady temperature, both rates must be equal K stands for Kelvin, a temperature scale where 0 K is absolute zero To convert K to F: TF = 1.8TK - 460 The Habitable Zone In order to support life a planet must be in the habitable zone Width of zone determined by the effectiveness of the carbonate-silicate cycle For our solar system habitable zone width is about 0.95-1.37 AU Too hot, water is destroyed can’t remove CO2 Too cold, try to warm up with more CO2 but CO2 forms clouds and blocks sunlight Just right, temperature kept stable at ~273 K (water is liquid) Hypothetical Habitable Zone Why is the Earth Habitable? It has the right temperature for liquid water (~273 K) because: Not too close or too far from the Sun Climate Two basic sources of convection The Earth’s rotation breaks the atmosphere up into convection cells that keep the air circulating, producing global weather patterns The Earth’s Surface What shapes the Earth’s surface? Also, volcanoes and cratering Resurfacing is cyclical and constant Unlike other planets the Earth does not have many craters Plate Tectonics The two top layers of the Earth are the crust and the mantle Crust is broken up into plates that float on the upper mantle Plates move around and crash into each other forming trenches and mountains How Plate Tectonics Work Plate Boundaries Water The Earth has more liquid water on its surface than any other planet Water is present on Earth in all three phases (ice, liquid water, vapor) and continuously cycles between them Water on the Earth Plate Collision -- The Himalayas The Grand Canyon Meteor Crater The Earth’s Interior The crust and atmosphere are very thin compared the rest of the planet (like the skin of an orange) We learn about them by studying the seismic waves from earthquakes Seismic Waves Types of waves: P waves: S waves: The different densities of the inner earth refract the waves When an earthquake occurs we can measure the strength of S and P waves all over the Earth Earthquake Studies of the Earth’s Interior Seismic Waves and the Earth’s Interior No S waves detected on opposite side of Earth There is a shadow zone where no P or S waves are detected Very faint P waves detected in shadow zone Structure of the Earth Structure of the Earth Crust: Mantle Outer core Inner core Density increases toward the center Summary Earth is unique for at least two reasons Large amounts of liquid water constantly reshapes the surface Large amounts of free oxygen produced by life Earth has liquid water and life because it is in the habitable zone Summary: Atmosphere Earth’s initial atmosphere composed of CHON H and O form water -- oceans C and O form carbon dioxide -- rock N stays in atmosphere Plants produce oxygen Mild temperature maintained by carbonate-silicate cycle Summary: Surface Solid iron inner core, liquid iron outer core, solid mantle and crust Crust is broken up into plates which slide around on the upper mantle Plate tectonics and erosion constantly alter surface