Week 3 in Class Notes
Week 3 in Class Notes ASTR 115
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This 5 page Class Notes was uploaded by Evan Kirkpatrick on Sunday October 18, 2015. The Class Notes belongs to ASTR 115 at University of Washington taught by in Fall 2015. Since its upload, it has received 22 views. For similar materials see INTRO ASTROBIOLOGY (NW) in Environmental Science at University of Washington.
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Date Created: 10/18/15
Week 3 in Class Notes Day 1 How do We Learn the History of the Planet Rocks 0 Igneous Molten material that solidi es when it hits the surface 0 Metamorphic When heat and pressure causes mineral chemical or structural change Not melting Occurs deep in the earth in extreme pressures and temperature 0 Sedimentary Layered compressed sediments from bodies of water or air fall Seismology 0 When earthquakes occur we are able to time the waves and deduce the internal composition of the Earth Layers of the Earth from the Outside to the Center 0 Crust 1064km o Asthenosphere100725km o Mantle Max thickness is 2980km Igneous rocks formed in the mantle 0 Outer Core 2260 km Liquid layer of molten iron and rock 0 Inner Core 1220 Slowly crystalizing into a nickel and iron core The Rock Cycle You can transfer any types of rocks to other kinds of rocks through temperature pressure melting deposition or erosion What are Rocks Made of Minerals A type of rock that is composed of a single type of molecule that form at speci c pressures and temperatures and have unique structure and composition 4000 distinct mineral types are known and are often grouped by their primary constituents 0 Eg Silicates are minerals that contain large amounts of silicon and oxygen Can be classi ed in numerous ways 0 Eg Grain or crystal size Small crystals are from fast cooling above the surface Large crystals are from slow cooling below the surface 23 of minerals are created by life Sedimentary Rocks and Fossils Fossils are normally only found in sedimentary rocks because other rocks require processes that would destroy the fossils 0 Eg Melting or extreme pressures Steno s Principles 1 Superposition In undisturbed sequences more deeply buried layers are older 2 Original Horizontality If we take 2 rock samples and they horizontally line up then we can assume that the similar layers occurred at the same time 3 Lateral Continuity If layers of two samples are similar then we can assume that a layer that we don t see of one of them is the same as the layer we can see in the other one Absolute Time Radiometric Dating A radioactive element s nucleus can undergo spontaneous change 0 Breaks apart or captures or releases electrons to turn a neutron into a proton or vice versa The halflife is the time it takes 50 of the quotparentquot atoms in a sample to change to another element quotdaughter atoms 0 Half lives are different for different isotopes Isotopes Isotopes An isotope is an atom that has the same number of protons but different number of neutrons C12 C13 are stable isotopes and don t decay C14 is unstable and radioactive Uranium238 goes through a process of decay until it reaches Lead206 which is nally stable 0 This whole process takes about 44 billion years so it is ideal for dating how old certain rocks are Geological Time Scale Divided into 4 types of eons Phanerozoic 541 Ma to present 0 Visible Lifequot fossils of plants and animals Proterozoic 25 Ga to 541 Ma 0 quotearlier lifequot fossils of mainly singlecelled organisms Archean 38 Ga to 25 Ga Geology and Astrobiology Solar System age can be determined by measuring the age of the meteorites 0 Earth is a bit younger than our solar system The Hadean Period 4538 Ga 0 First 700 billion years of Earth s history 0 Earth formed with a fraction of water rich planetesimals Water released as steam via volcanism Volcanic gases H20 C02 N2 S02 H2S H2 This quotoutgassingquot provided the water for our oceans and gases for the atmosphere Atmosphere was likely C02 N2 and water vapor dominated No 02 o Oceans and early continents had probably formed by 44 Ga 0 Moon is key because we ve been there taken samples and done radiometric dating White features are highlands formed about 44 bya Dark features are quotmarequot or valleys formed about 393 bya More recent rock has few craters Late Heavy Bombardment 39 to 38 bya 0 Moon Formation Giant Impact Hypothesis A planetesimal crashed into Earth at a glancing blow and heated up the Earth Remaining part of the planetesimal began to orbit the Earth and accrete nearby material Eventually became our moon Earth s Interior Key to magnetic eld and tectonics Lithosphere Rigid outer part of Earth which includes crust and upper mantle o This is broken into plates Crust Has distinct mineral composition compared to mantle Common Error To con ate crust and lithosphere The outer core remains liquid because its not ender enough pressure to solidify and it s hot Outer core convection creates electric currents which in turn create a magnetic eld Energy Sources in Earth Differentiation Settling of heavy elements to center releases energy Inner Core Nucleation Solidi cation of core releases latent heat Radiogenic Heating Radioactive decay o Mainly in mantle 0 13 to 12 of heat from radioactive decay o Geoneutrinos are released during radioactive decay and We have built things that use neutrinos to measure Earth s power Heat Form Formation Leftover energy from Moonforming impact Global Magnetic Fields What do we need 0 An interior region of electrically conducting uid such as molten metal 0 Convection in that layer They protect our atmosphere 0 A magnetic eld protects against quotsolar wind strippingquot of a planetary atmosphere 0 Particles are de ected around the Earth a few come in at the poles causing aurorae Plate Tectonics Earth is the only planet in the Solar System with plate tectonics Earth is the only habitable planet Coincidence To have plate tectonics you need heatdriven mantle convection and a lithosphere thin enough to be fractured by the movement of the mantle Plates spread apart on sea oors and collide and subduct at ocean trenches Some plates collide and push the crust upward Himalayas Hot spot volcanism 0 Present on Earth in the middle of plates but may be the only way for some planets and moons to release internal energy The Carbon Cycle Helps in understanding the surface and atmosphere of the Earth including effects on life This climate stabilizing cycle that operates on million year timescales is called the carbonate silicate cycle 0 Too slow to help with humaninduced global warming Snowball Earth The icecaps grow towards the equator o lcecaps re ect light which makes the planet colder o This creates a positive feedback loop where the Earth just continues to get covered in ice and colder and colder There is no way for the C02 to get back into the ocean because it is all ice so slowly the atmosphere gets lled with C02 and heats the planet 0 Eventually the ice starts to melt and another positive feedback loop where the Earth melts the ice and gets hotter which melts more ice Always end back in the same state you were in Snowball Earth is not an Ice Age 0 Snowball All of Earth is covered in snow Can last tens of millions of years 0 Ice Ages Partially covered in ice Lasts millions of years Ice Ages What causes ice ages 0 Changes in Earth s orbit Change in Earth s tilt Volcanic Eruptions Fluctuations in the Sun Changes in Ocean Currents This ice age triggered by connection of North and South America 0000 Our Atmosphere 5 layers of our atmosphere are de ned by temperature in ections From highest to lowest 0 Exosphere 500 km 0 Thermosphere 80km 500 o Mesosphere 50km 80km o Stratosphere 10km 50km Contains maximum ozone layer hot section 0 Troposphere 0km 10km Planetary Surface Temperature Earth s temperature is determined by 3 things 0 1 Amount of incident solar radiation 0 2 How much sunlight is re ected Albedo o 3 quotGreenhouse Warmingquot Trapping of sunlight near the surface by gases ike C02 H20 and CH4 0 Anything with a nite temperature emits radiation The hotter it is the shorter the peak wavelength Blue light is hotter than red The Greenhouse Effect Sunlight comes in through the atmosphere and warms up the surface of the Earth Because Earth is heated it will then emit radiation Greenhouse gases trap this radiation and continues to heat the Earth Some molecules are transparent in visible light but opaque in the infrared 0 These are greenhouse gases The infrared light does not immediately escape to space 0 Causes surface warming Works on every planet with an atmosphere and molecules ike CO2
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