Notes of a Geobiology Watcher, or How to Love Your Bacteria Interactions Between Life Forms And The Earth’s Physical And Chemical Systems Prepared by Michael McGoodwin (MCM) Autumn 2007 TABLE OF CONTENTS Introduction and Disclaimers ...................................................................................................................................................3 Instructors, Website, and Recommended Textbooks .............................................................................................................4 Geobiology Journal..........................................................................................................................................................4 LECTURE-RELATED MATERIALS ....................................................................................................................................4 Definition of Geobiology and Course Emphases.....................................................................................................................4 Topics of Study in Geobiology..................................................................................................................................................5 Typical Geobiological Research Questions.....................................................................................................................5 What is Life?..............................................................................................................................................................................6 Some of the relevant issues and questions:......................................................................................................................6 Characteristics of Life as we know it:..............................................................................................................................7 What are the essential characteristics of life? (How could extraterrestrial life differ and still be life?) ..........................8 Origin Of Life (How Did Life Start?) ......................................................................................................................................9 Extraterrestrial Life ................................................................................................................................................................17 Habitable Planets: Factors Predisposing to Habitability .....................................................................................................18 Presumed Characteristics of Habitable Planets (and Moons) ........................................................................................18 Water and Ice Line ........................................................................................................................................................21 Circumstellar Habitable Zone........................................................................................................................................22 Faint Young Sun Paradox..............................................................................................................................................24 Runaway Greenhouse Effect .........................................................................................................................................25 Galactic Habitable Zone (GHZ) ....................................................................................................................................25 Potential Sites of Life in the Solar System ....................................................................................................................26 Martian Life...................................................................................................................................................................28 Life Outside the Solar System .......................................................................................................................................31 Panspermia.....................................................................................................................................................................31 How Did Earth Become Habitable? (Early Earth History) .................................................................................................31 1. When did Earth form? ...............................................................................................................................................32 2. Moon Forming Impact (and Attainment of Final Earth Mass): .................................................................................33 3. Earth Differentiation: When Did the Core Segregate From The Mantle? .................................................................35 4. Crustal Differentiation...............................................................................................................................................36 5. Where Did The Atmosphere Come From? ................................................................................................................37 6. When Did The Oceans Condense? ............................................................................................................................38 7. Impact Frustration of Life..........................................................................................................................................38 Archean Environment.............................................................................................................................................................39 1. Was Surface Temperature Similar to Present? ..........................................................................................................39 2. Were Day Length and Size of Tides Different in the Archean? ................................................................................41 3. Tectonic Evolution: How Early Did Plate Tectonics Start?.......................................................................................43 First Signs of Life (When Did Life First Appear?)...............................................................................................................46 1. Difficulties in Detecting Earliest Life........................................................................................................................46 2. Microfossils ...............................................................................................................................................................47 3, Stromatolites..............................................................................................................................................................48 4. Isotope Fractionation As Evidence of Archean Life:.................................................................................................49 Domains of Life........................................................................................................................................................................51 1. Construction of the Tree of Life (TOL).....................................................................................................................51 2. Pattern of the Tree of Life: Three Domains...............................................................................................................53 3. Bacteria Domain, Specific Additional Details...........................................................................................................57 4. Archaea Domain ........................................................................................................................................................62 5. Eukaryote Domain.....................................................................................................................................................65 GeobiologyESS313.doc 4/13/2008 21:21 Page 1 of 225 Biochemical Cycles ..................................................................................................................................................................67 1. Characteristics of Biochemical Cycles ......................................................................................................................67 2. Carbon Cycles............................................................................................................................................................67 Short Term Organic Carbon Cycle ........................................................................................................................68 Long Term Organic Carbon Cycle: .......................................................................................................................70 Inorganic Carbon Cycle.........................................................................................................................................71 3. Sulfur Cycle...............................................................................................................................................................73 4. Nitrogen Cycle...........................................................................................................................................................75 Microbial Mineralization ........................................................................................................................................................76 1. Carbonate Precipitation in Stromatolites ...................................................................................................................76