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No part of this book may be reproduced in any form – by photoprinting, microfilm, or any other means – nor transmitted or translated into a machine language without written permission from the publishers. Registered names, trademarks, etc. used in this book, even when not specifically marked as such, are not to be considered unprotected by law. Typesetting Dçrr + Schiller GmbH, Stuttgart Printing betz-Druck GmbH, Darmstadt Binding Litges & Dopf Buchbinderei GmbH, Heppenheim Printed in the Federal Republic of Germany Printed on acid-free paper ISBN: 978-3-527-40660-9 V Table of Contents 1 Astrobiology: From the Origin of Life on Earth to Life in the Universe Andr Brack 1.1 General Aspects of Astrobiology 1 1.1.1 Historical Milestones 1 1.1.2 Searching for Emerging Life 3 1.1.3 The Role of Water 4 1.1.4 The Physicochemical Features of Carbon-based Life 4 1.1.5 Clays as Possible Primitive Robots 6 1.2 Reconstructing Life in a Test Tube 7 1.2.1 The Quest for Organic Molecules 7 1.2.1.1 Terrestrial Production 7 1.2.1.2 Delivery of Extraterrestrial Organic Molecules 8 1.2.2 Space Experiments 10 1.2.3 Attempts to Recreate Life in a Test Tube 11 1.2.4 A Primitive Life Simpler than a Cell? 13 1.3 The Search for Traces of Primitive Life 14 1.3.1 Microfossils 14 1.3.2 Oldest Sedimentary Rocks 15 1.4 The Search for Life in the Solar System 15 1.4.1 Planet Mars and the SNC Meteorites 15 1.4.2 Jupiter’s Moon Europa 17 1.4.3 Saturn’s Moon Titan 18 1.5 The Search for Life Beyond the Solar System 19 1.5.1 The Search for Rocky Earthlike Exoplanets 19 1.5.2 Detecting Extrasolar Life 20 1.6 Conclusions 20 1.7 Further Reading 21 1.7.1 Books and Articles in Books 21 1.7.2 Articles in Journals 21 1.7.3 Web Sites 22 Complete Course in Astrobiology. Edited by Gerda Horneck and Petra Rettberg Copyright 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim ISBN: 978-3-527-40660-9 VI Table of Contents 2 From the Big Bang to the Molecules of Life Harry J. Lehto 2.1 Building Blocks of Life 23 2.2 Big Bang: Formation of H and He 25 2.3 First Stars: Formation of Small Amounts of C, O, N, S and P and Other Heavy Elements 28 2.4 Normal Modern Stars, Bulk Formation of C, O, N, S, P and Other Heavy Elements 29 2.5 The First Molecules (CO and H2O) 35 2.6 Interstellar Matter 35 2.6.1 Interstellar Clouds 37 2.6.2 Interstellar Grains 39 2.6.2.1 Formation 39 2.6.2.2 Observed Properties 40 2.6.3 Ices 41 2.6.4 Molecules in the Gas Phase 42 2.6.4.1 Observed Properties 42 2.6.4.2 Formation of H2 43 2.6.4.3 Formation of CO and H2O 44 2.7 Generation of Stars: Formation of the Sun and Planets 44 2.7.1 Accretion Disk of the Sun 44 2.7.2 Formation of the Earth 46 2.7.3 Early Rain of Meteorites, Comets, Asteroids, and Prebiotic Molecules 47 2.7.4 D/H Ratio and Oceans 49 2.8 Further Reading 51 2.8.1 Books or Articles in Books 51 2.8.2 Articles in Journals 51 2.8.3 Web Sites 53 2.9 Questions for Students 53 3 Basic Prebiotic Chemistry Herv Cottin 3.1 Key Molecules of Life 55 3.1.1 Dismantling the Robots 56 3.1.2 Proteins and Amino Acids 58 3.1.3 DNA, RNA, and Their Building Blocks 60 3.1.4 First “Prebiotic Robot” 63 3.2 Historical Milestones 63 3.3 Sources of Prebiotic Organic Molecules 69 3.3.1 Endogenous Sources of Organic Molecules 69 3.3.1.1 Atmospheric Syntheses 69 3.3.1.2 Hydrothermal Vents 70 3.3.2 Exogenous Delivery of Organic Molecules 71 3.3.2.1 Comets 71 3.3.2.2 Meteorites 73 Table of Contents VII 3.3.2.3 Micrometeorites 74 3.3.3 Relative Contribution of the Different Sources 74 3.4 From Simple to Slightly More Complex Compounds 75 3.4.1 Synthesis of Amino Acids 75 3.4.2 Synthesis of Purine and Pyrimidine Bases 76 3.4.3 Synthesis of Sugars 78 3.4.4 Synthesis of Polymers 80 3.5 Conclusions 81 3.6 Further Reading 82 3.6.1 Books or Articles in Books 82 3.6.2 Articles in Journals 82 3.7 Questions for Students 83 3.7.1 Basic-level Questions 83 3.7.2 Advanced-level Questions 83 4 From Molecular Evolution to Cellular Life Kirsi Lehto 4.1 History of Life at Its Beginnings 85 4.2 Life as It Is Known 88 4.2.1 The Phylogenetic Tree of Life 88 4.2.2 Life is Cellular, Happens in Liquid Water, and Is Based on Genetic Information 88 4.2.2.1 Genetic Information 92 4.2.2.2 The Genetic Code and Its Expression 94 4.3 Last Universal Common Ancestor (LUCA) 96 4.3.1 Containment in a Cell Membrane 97 4.3.2 Genes and Their Expression 99 4.3.3 Hypothetical Structure of the LUCA Genome 103 4.4 “Life” in the RNA–Protein World: Issues and Possible Solutions 105 4.4.1 Evolutionary Solutions 106 4.4.2 Solutions Found in the Viral World 107 4.5 “Life” Before the Appearance of the Progenote 108 4.5.1 The Breakthrough Organism and the RNA–Protein World 108 4.5.2 Primitive Translation Machinery 108 4.5.3 Origin of Ribosomes 109 4.6 The RNA World 111 4.6.1 Origin of the RNA World 113 4.6.1.1 Prebiotic Assembly of Polymers 113 4.6.1.2 The Building Blocks of the RNA World 114 4.6.1.3 Where Could the RNA World Exist and Function? 115 4.7 Beginning of Life 117 4.8 Further Reading 118 4.8.1 Books 118 4.8.2 Articles in Journals 118 4.9 Questions for Students 120 VIII Table of Contents 5 Extremophiles, the Physicochemical Limits of Life (Growth and Survival) Helga Stan-Lotter 5.1 A Brief History of Life on Earth 121 5.1.1 Early Earth and Microfossils 121 5.1.2 Prokaryotes, Eukaryotes, and the Tree of Life 123 5.1.3 Some Characteristics of Bacteria and Archaea 126 5.1.3.1 Cell Walls, Envelopes, and Shape 126 5.1.3.2 Lipids and Membranes 127 5.2 Extremophiles and Extreme Environments 127 5.2.1 Growth versus Survival 129 5.2.2 The Search for Life on Mars: The Viking Mission 130 5.2.3 Temperature Ranges for Microorganisms 132 5.2.4 High-temperature Environments 133 5.2.4.1 Geography and Isolates 133 5.2.4.2 Molecular Properties of Hyperthermophiles 136 5.2.4.3 Early Evolution and Hyperthermophiles 137 5.2.4.4 Applications 138 5.2.5 Low-temperature Environments 138 5.2.5.1 Geography and Isolates 138 5.2.5.2 Molecular Adaptations 139 5.2.6 Barophiles or Piezophiles 140 5.2.7 High-salt Environments 140 5.2.7.1 Hypersaline Environments and Isolates 140 5.2.7.2 Viable Haloarchaea from Rock Salt 141 5.2.7.3 Molecular Mechanisms 142 5.2.7.4 Extraterrestrial Halite 143 5.2.8 Subterranean Environments 144 5.2.9 Radiation 145 5.3 Microbial Survival of Extreme Conditions 146 5.4 Conclusions 148 5.5 Further Reading 149 5.5.1 Books or Articles in Books 149 5.5.2 Articles in Journals 149 5.5.3 Web Sites 150 5.6 Questions for Students 150 6 Habitability Charles S.