Suspended Space Shuttle Endeavor Mesosphere Stratosphere Troposphere 9 Feb 2010 Image Credit NASA Crew of Expedition 22 Course Announcements Quiz 3 available for collection ESA s ExoMars Trace Gas Orbiter TGO successfully in orbit ESA s ExoMars Schiaparelli Lander likely did not survive the landing but that wasn t the point Entry descent and landing Demonstrator Module EDM designed to test European Mars landing technology Upcoming Class Schedule Quiz 4 on Monday 24 October Exam 2 on Friday 28 October Will be releasing study materials and planning study sessions more info to come soon Assignments Reading Assignments No new reading Parallel Lectures CC Astronomy Episode 11 The Earth watch if you haven t yet Mastering Astronomy Chapter 7 Homework Due Monday 21 October at 11 59 PM EDT Quiz 3 Results Best quiz grade wise yet Raw w Bonus Point Mean 7 8 8 7 Median 8 0 9 0 Typo in Gas Giant Planet formation hypotheses question Core collapse Core accretion Credit given to everyone Very few instances of sharing Bonus Point Keyword Dumbledore Thanks for the honesty The Earth CHAPTER 7 Earth s General Stucture Mass 6 x 1024 kg 5 97 x 1024 kg Radius 6 400 km 6378 km Avg Density 5500 kg m3 or 5 5 g cm2 Inner Core 0 1300 km Outer Core 1300 3500 km Mantle 3500 6350 ish km Crust 5 50 km thick Oceanic Crust 5 km thick Continental Crust 30 50 km thick Hydrosphere All water Atmosphere Crust 100 km Magnetosphere 100 km The K rm n Line flight not possible Atmosphere technically extends to infinity Atmosphere Different than expected The composition of our atmosphere is not like our expectation of a secondary atmosphere dominated by CO2 Gas Formula by Volume Main Constituents Nitrogen N2 78 Oxygen O2 21 Argon Ar 0 9 Trace Gases Carbon Dioxide CO2 0 03 Other The rest Variable Amount Water Vapor H2O 0 1 3 0 Earth s early Secondary Atmosphere is expected to be mostly CO2 about 95 How did it becoming nitrogen dominated Where did the oxygen come from Origin of Earth s Atmosphere Not like the expected Secondary Atmosphere what gives Sarychev Eruption from ISS Earth s gravity too low to keep the primary atmosphere of hydrogen and helium inherited from the Solar Nebula Volcanic outgassing released gases trapped in Earth s interior create a secondary atmosphere Water vapor methane CO2 sulfur dioxide and nitrogen compounds N2 Ammonia nitric oxide etc Origin of Earth s Atmosphere Altering the Secondary Atmosphere Volcanic outgassing of water vapor methane CO2 sulfer dioxide and nitrogen compounds N2 Ammonia nitric oxide etc generate Earth s Secondary Atmosphere Expectation is primarily CO2 atmosphere Our atmosphere has significantly changed since then Photodissociation sunlight primarily UV light breaking apart molecules broke these molecules apart forming Inert non reactive N2 forms and builds up Loss of hydrogen atoms to outer space Water condensed into oceans and dissolves much of the CO 2 and sulfur dioxide Remaining CO2 sulfur dioxide etc reacts with surface rocks and becomes incorporated into the rocks Origin of Earth s Atmosphere Still need Oxygen Oxygen is very chemically reactive so why here Requires constant replenishment Life appeared in the oceans some 3 5 billion years ago but it wasn t until about 2 5 billion years ago that photosynthetic organisms cyanobacteria released oxygen O2 into the atmosphere Transition to dominance of photosynthetic life and oxygen in the atmosphere called the Great Oxidation Event Cyanobacteria Bloom Credit NASA MODIS Cyanobacteria Credit Queen Mary Univ Origin of Earth s Atmosphere Summary UV Light Photodissociates Nitrogen Compounds Free hydrogen escapes to space NH3 H NH3 N N CO2 SO2 H N2 Nitrogen N2 builds up in atmosphere Summary CO2 SO2 become part of oceans and rock Light splits nitrogen compounds and forms N2 which builds up in atmosphere Photosynthetic life provide O2 to atmosphere Left with N2 and O2 rich atmosphere 2 5 Billion Years ago Gya cyanobacteria generate O2 via photosynthesis O2 CO2 and SO2 dissolve in oceans and become part of the rocks Earth s Atmosphere Composition Our Oxygen makes us unique Gas Formula by Volume Main Constituents Nitrogen N2 78 Oxygen O2 21 Argon Ar 0 9 Trace Gases Carbon Dioxide CO2 0 03 Other The rest Variable Amount Water Vapor H2O 0 1 3 0 99 Earth s Atmosphere Lower Layers Ionosphere Thermosphere 100 km 80 km Ionized molecules and free electrons Mesophere 50 80 km Stratosphere 17 50 km Contains Ozone Layer Calm air where planes fly Troposphere 0 17 km Convection Occurs Place where weather is 80 of the mass Temperature K Earth s Atmosphere Lower Layers Boundaries between layers occur at temperature inversions How temperature changes with altitude switches Stratosphere increases in temperature with altitude due to ozone O3 absorbing UV sunlight Temperature K Troposphere Where weather happens In the Troposphere air is constantly being moved around through convection driven by Earth s warm surface Convection is the transfer of heat from one place to Convection Cell another through the movement of a gas or liquid Cools Down Warms Up Convection in Troposphere In Earth s Atmosphere Each circulation unit called is called a Convection Cell Sunlight Heats Surface Heat IN Convection In Earth s Atmosphere Earth s Surface warms the air above it This warm air is less dense thanks Ideal Gas Law and therefore rises i e it becomes buoyant wants to float upward As it rises the air cools and become more dense i e less buoyant and will sink back down toward the warm surface where it can warm back up Wash rinse repeat and you establish a cycle of upwelling warm air and concurrent downward flow of colder air arranged in circulation units called convection cells This is what causes Earth s weather Global winds trade winds jet stream etc local winds clouds storms hurricanes typhoons tornadoes etc Stratophere The calm ozone layer Where planes fly and where ozone lives No convection in the stratosphere so very calm why planes fly in this layer Ozone O3 is excellent absorber of UV photons Why there is a temperature inversion such that the stratosphere gets warmer with as you go higher in altitude UV radiation can cause damage to cells and so the Ozone Layer protects us and all life yea Altitude km There is a sharp peak in the amount of ozone about 10 parts per million at about 20 30 km above the surface Below this there are on average about 0 3 parts per million of ozone molecules Amount of ozone parts per million The Ozone Hole Large hole in the ozone
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