EAS 210 Study Notes.docx

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Earth and Atmospheric Sciences
Jeremy Richards

EAS 210 Study Notes Origins of the Earth  Universe originally 98% hydrogen and helium, 2% heavier elements  Heavier elements came from nucleosynthesis (dying stars)  Big Bang  13.7 Billion years ago (13.7 Ga)  Since then universe has been expanding  Picture here  Crust Formation  Primitive crust formed as lighter, silica rich material and solidified at surface  Early crust recycled to form continental crust ~2.5 Ga  Oceanic crust continues to be formed and recycled today  Continental Crust  Averages 40km thick (<= 70km)  Made up of lower density (~2.7g/cm^3) silica rich rocks  Oceanic Crust  Averages 7km thick (3-15km) made up of higher density (~3.0g/cm^3) silica poor rocks  Lithosphere  Rigid outer layer which includes the crust and part of the upper mantle  ~100km thick  Asthenosphere  Behaves plastically and extends ~200km  Moho  Density boundary b/w crust and boundary  Seen by change in speed of seismic waves  The boundary between asthenosphere and lithosphere is seen by the composition of rocks  Felsic Rocks (silicic or acidic)  Rocks rich in silica….feldspars and quartz  Lower density ~2.7g/cm^3  Mafic rocks (basic)  Poor in silica and rich in magnesium and iron  ~3.0g/cm^3 Composition of Earth  Principle of Isostasy  Lighter crust “floats’ on underlying denser ultramafic rocks  Dratts theory  Blocks of same mass but differing density  Describes continental crust and oceanic crust  Airy’s Theory  Blocks of same density, different masses  Thick continental crust rises higher than thinner continental crust (mountains)  Note that seawater does not affect crusts… it just fills in the low places  Formation of Early atmosphere  Large volumes of volatiles (hydrogen, water, nitrogen, carbon dioxide) released from primitive mantle via magmas erupted at surface and formed the early atmosphere  Lost most hydrogen to space. Only retained heavier gasses  Oxygen not built up in atmosphere until photosynthesizing organisms first appeared (~2.5 Ga)  Liquid water is the most unique feature of Earth  Ocean vastly unexplored  Large component in plate tectonics  Timeline for life  ~3.85 Ga earliest evidence for life  550Ma evolutionary big bang  First humans appeared ~4Ma ago  Homo sapiens only ~200000 years ago Atomic Compounds and Minerals  Isotopes- same amount of protons but different amounts of neutrons  12C and 13C and 14C. The last which is radioactive  Radioactive isotopes have half-life’s, which is the time in which it takes the isotope to be present in half its original concentration  Generally at 10 ½ lives concentration is essentially 0 and cannot be measured with any form of accuracy  Radioactive Decay – Its Natural  Alpha particle emission (nucleus loses 2n+2p)  Beta particle emission (which converts neutron to proton)  Electron Capture (which converts proton to a neutron)  Rubidium  ½ life of 48.83 billion years  87Rb weakly radioactive, breaks down by beta emission  Turns into 87Sr  Uranium  Long decay sequence  Intermediate step 222Rn is very dangerous  Nuclear Fission  Occurs when nuclei of large atoms split apart. Releases nuclear energy and neutrons possibly leading to more fission  Nuclear Fusion  Nuclei of small atoms fuse together  Like the sun (2H and 3H form 4He) Mineralogy  Mineral: A naturally occurring, inorganic, crystalline solid with a narrowly defined chemical composition and characteristic physical properties.  Poly morphs : same mineral, different shape  Physical Properties of minerals  Hardness  Cleavage – best seen in micas, different than habit and fracture  Fracture  Lustre  Metallic  Adamantite  Vitreous  Resinous  Greasy  Pearly  Silk  earthy  Color  Streak (Hematite)  Density  Crystal habit  MOH’s hardness scale  10-Diamond  9-Corundum  8-Topaz  7-Quartz  6-Orthoclase  5-Apatite  4-Fluorite  3-Calcite  2-Gypsum  1-Talc  Steel file is 6.5, glass is 5.5, copper is 3.5, fingernail is 2.5\ Coal Energy, Hydrocarbons  The types of energy we have used as humans have changed greatly with time. From wood to coal to hydrocarbons  Coal is abundant but dirty  Formed by progressive burial of plant matter  Plant matter decays in the absence of oxygen (underwater) subbitumous bituminous anthracite Peat Lignite coal coal coal graphite  Oil and Gas  Formed by progressive burial of organic matter  Oil and gas float on water and head towards surface so we look for places where they get trapped by impermeable cap rocks  Tar sands – large reserves but expensive to extract  Nuclear Power  No greenhouse gases  Socially unacceptable due to waste disposal Rocks and Rock Cycle     There are 3 main rock types  Sedimentary  Sedimentary Process  Uplift  Weathering and erosion  Transport  Deposition  Lithification, diagenesis  Igneous  Rock formed by solidification of magma  Metamorphic  Mineralogical and textual changes in rocks due to changes in pressure and temperature  Migmatite – partially molten metamorphic rock  Gneiss – high grade metamorphic rock  Two types of metamorphism  Regional – (tectonic plates colliding)  Contact – Rocks touching a pocket of magma Igneous Processes  Magma is a molten rock  Igneous rock is a solidification of magma  Texture  Extrusive – fast cooling – fine grained  Intrusive – slow cooling – coarse grained    Partial Melting in the crust and Mantle  Mafic magmas formed by melting of the ultramafic mantle  Felsic magmas formed by melting of felsic, continental crust  Intermediate magmas formed by interaction of mafic magmas with continental crust  Magmatic process  Partial melting – eutectic mel
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