Transcript 12earth6s
Earth Astronomy 311 Professor Lee Carkner Lecture 12 Terra -- The Earth Goddess We use the old English names for the Earth, Sun and Moon, rather than the Latin ones Earth Facts Size: 12700 km diameter Orbit: 1 AU (1.5 X 108 km) Description: wet, temperate, inhabited Earth’s Atmosphere Composition: 21% O2 Very different from other atmospheres Outer planets: mostly H2 Early Atmosphere Where did the original atmosphere come from? Bombardment of icy planetesimals (comets) Early composition: Water (H2O) Ammonia (NH3) Formation of Atmosphere Ultraviolet light breaks up some molecules (four key elements: C,H,O,N) CO2 dissolves in H2O, H2O rains out to form oceans, N2 left behind Life (plants) forms and produces O2 Final atmosphere -- O2 and N2 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 Inner Edge -- where water is lost by UV dissociation Outer Edge -- Note: planet needs to be large enough to have atmosphere and plate tectonics 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 Planet Temperature Can estimate a planet’s temperature by radiation balance: Emit radiation back into space Note: this assumes the planet is just a big uniform ball with no atmosphere or climate Remember 0 K is absolute zero and 300 K is about room temperature TF = 1.8TK - 460 Radiative Power Hot objects absorb and emit energy based on the Stefan-Boltzmann law P = sAT4 Where: s is a constant = 5.67 X 10-8 (W/(m2 K4)) for a sphere A = 4pr2 T is the temperature of the object (in K) Energy Balance If we compare the energy the Earth emits with the energy it gets from the Sun, we can find its temperature TE = [RS/(2 DS)]½ TS Where: TE TS is the temperature of the Sun RS DS is the distance from the Earth to the Sun Plate Tectonics The two top layers of the Earth are the crust and the mantle Crust is hard and rigid Plates move around and crash into each other forming trenches and mountains Plate tectonics and water resurface the Earth Most other planets resurfaced by volcanism and cratering How Plate Tectonics Work Plate Boundaries Plate Collision -- The Himalayas Seismic Waves Types of waves: P waves: pressure or compression wave example: S waves: shear waves example: 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 Core must be liquid There is a shadow zone where no P or S waves are detected Very faint P waves detected in shadow zone Refracted by solid inner core Structure of the Earth Structure of the Earth Crust: surface to 35 km Outer core 2900-5100 km Mantle 35-2900 km composed of silicates and heavier material Inner core 5100-6400 km composed of solid iron Next Time Read Chapter 8 Just the moon parts 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