Astrobiology An Introduction

Astrobiology is a multidisciplinary pursuit that in various guises encompasses astronomy, chemistry, planetary and Earth sciences, and biology. It relies on mathematical, statistical, and computer modeling for theory, and space science, engineering, and computing to implement observational and experimental work. Consequently, when studying astrobiology, a broad scientific canvas is needed. For example, it is now clear that the Earth operates as a system; it is no longer appropriate to think in terms of geology, oceans, atmosphere, and life as being separate. Reflecting this multiscience approach, Astrobiology: An Introduction: Covers topics such as stellar evolution, cosmic chemistry, planet formation, habitable zones, terrestrial biochemistry, and exoplanetary systems Discusses the origin, evolution, distribution, and future of life in the universe in an accessible manner, sparing calculus, curly arrow chemistry, and modeling details Contains problems and worked examples, and includes a solutions manual with qualifying course adoption Astrobiology: An Introduction provides a full introduction to astrobiology suitable for university students at all levels.

Constants Acknowledgments Author Introduction Origin of the Elements Elements for Life The Universe Started from a Hot and Dense State Abundances of Primordial Elements Are Predicted by the Big Bang Hypothesis The Message of Light Atoms and Molecules Process Electromagnetic Radiation Electronic Transitions Are Quantized Energy Levels Govern Electronic Transitions in the Hydrogen Atom Spectrographs Are Used to Capture Spectra Stellar Spectra Encode Temperature and Elemental Abundances Stellar Evolution The Properties of Main Sequence Stars Are Determined by Their Masses Stars Form by the Collapse of Giant Molecular Clouds Protostars Contract Down Onto the Main Sequence Main Sequence Stars Fuse Hydrogen to Helium Many Low Mass Stars Become Red Giants High Mass Stars Make High Mass Elements The Chemistry of Space From Elements to Molecules Astrochemical Environments Cool Stars Have Molecular Absorption Lines The Interstellar Medium Is Extremely Tenuous The ISM Contains Dust Grains AGB Stars Have Either Oxygen- or Carbon-Rich Atmospheres Doing Chemistry in Space Different Chemistry Operates in Dense Clouds and Diffuse Clouds Molecular Spectroscopy Molecules Are Detected Mostly by Vibrational and Rotational Spectra Building Molecules Molecules in the ISM Reaction Mechanisms Chemical Networks Dust Grain Surfaces Catalyze Synthesis of Hydrogen Molecules Chemical Species Can Trace ISM Conditions and Processes Habitable Earth Earth in Context There Are Eight Major Planets The Planets Were Condensed from a Spinning Disc The Solar System Contains Numerous Small Bodies What Is a Planet? Habitability Is an Attribute of the Entire Earth System The Structure and Composition of the Solid Earth The Chondritic Earth Model Provides a First Approximation to Its Bulk Composition Seismology Provides a Picture of the Earth’s Interior What Makes Earth Habitable? Temperature at the Earth’s Surface Is Largely Determined by the Sun Liquid Water Exists on the Earth’s Surface Earth Is in a Stable Orbit in the Habitable Zone Earth’s Dense Atmosphere Contributes to Habitability A Global Magnetic Field May Be Required for Habitability Earth Seems Unique in Having Plate Tectonics Plate Tectonics Depends on a Weak Mantle Layer New Ocean Crust Is Made at Constructive Plate Boundaries Ocean Crust Is Destroyed at Destructive Plate Boundaries Hot Spot Volcanism: Evidence for Mantle Convection? Plate Tectonics Is Self-Regulating Plate Tectonics May Be Required for Habitability Plate Tectonics Seems Not to Operate on Mars or Venus Building the Solar System Planet Formation Is Contingent Planets Formed by Accretion from the Solar Nebula The Solar Nebula Was a Dynamic Environment The Solar Nebula Formed a Spinning Disc Planet and Star Formation Occur Together Condensation of Solids from the Solar Nebula Depended on Temperature Accretion Involves Several Distinct Mechanisms Heat Sources Drive Differentiation Differentiation Redistributes Elements Gas Giants Must Have Assembled Within a Few Million Years Accretion of Terrestrial Planets Took Tens of Millions of Years The Solar System Started with a Bang 26Mg Traces the Original 26Al Did the Decay of 26Al Make Life on Earth Possible? Dating Events in the Early Solar System Relies on Radioactive Isotopes Radiometric Dating Relies on the Exponential Decay of Radioisotopes Radiometric Dating Uses Isochron Plots Planetary Migration Is Required to Resolve Several Paradoxes Theories of Planetary Migration Have Been Derived Some Features of Solar System Architecture Have Been Hard to Explain The Nice Model Accounts for Solar System Architecture by Planetary Migration Early Earth Assembly of the Earth Can Be Modeled To First Approximation Earth Grew at a Decreasing Exponential Rate Accretion Was Probably Heterogeneous Early Earth Was Shaped by a Moon-Forming Impact The Moon-Forming Impact Is Supported by Theory and Geochemistry The Timing of the Moon-Forming Impact Is Poorly Constrained Tidal Forces Drove Evolution of the Earth–Moon System The Early Hadean Was Hot Earth’s Postimpact Atmosphere Was Largely Rock Vapor A Magma Ocean Remained After the Moon-Forming Impact The Hadean Mantle, Atmosphere, and Oceans Could Have Coevolved A Dry Accreting Earth Would Be Hot During the Hadean Late Events Modified the Composition of the Earth Earth’s Mantle and Crust Has an Excess of Siderophile Elements Core Separation Happened at High Pressure and Temperature Siderophile Elements Were Likely Delivered by a Late Veneer The Mantle Has Become More Oxidized with Time How Did the Terrestrial Planets Acquire Water? The Water Inventory of the Earth Is Not Well Known Did Terrestrial Planets Accrete Dry? Did Terrestrial Planets Accrete Wet? Volatile Delivery Could Have Occurred Late The Temperature of the Late Hadean and Archaean Are Not Well Constrained Geological Clues Suggest Early Earth Was Warm Rather Than Hot When Did the First Oceans Form? Plate Tectonics on Early Earth When Did Plate Tectonics Start on Earth? Plate Tectonics May Not Have Operated in the Hadean What Was the Nature of Early Plate Tectonics? Earth’s Atmosphere Has Changed over Time Earth’s Atmosphere May Come from Two Sources The Oxidation State of the Atmosphere Has Altered Nitrogen May Be Derived from Ammonia The Faint Young Sun Paradox Properties of Life Can Life Be Defined? Life Is a Complex, Self-Organizing, Adaptive Chemical System The Chemistry of Life Is Far from Equilibrium Life Requires an Energy Source Living Systems Are Capable of Self-Replication Life Exhibits Darwinian Evolution How Useful Are These Criteria for Detecting Life? Are There Universal Chemical Requirements for All Life? No Element Is More Versatile in Its Chemistry than Carbon Water as a Universal Solvent Terrestrial Biochemistry Building Blocks for Life Polymeric Macromolecules All Life on Earth Consists of Cells Information Flow in Cells All Life on Earth Has One of Two Basic Cell Architectures Gene Transfer Can Occur Vertically or Horizontally All Life on Earth Falls into Three Domains DNA Is the Universal Replicator All Life on Earth Uses DNA DNA Replication Was Deduced from Theory DNA Acts as a Template Metabolism Matches Lifestyle Living Systems Enhance Reaction Kinetics Life on Earth Has Three Metabolic Requirements Cells Harness Free Energy Respiration Requires an Exogenous Electron Acceptor Most Carbon Oxidation Happens in the Krebs Cycle Electron Chains "Quantize" Free Energy Availability ?G°' of Redox Reactions Can Be Calculated Proton Gradients Are the Core of Terrestrial Metabolism Anerobic Respiration Uses Electron Acceptors Other Than Oxygen Fermentation Uses an Endogenous Electron Acceptor Phototrophs Harvest Sunlight Not All Photosynthesis Produces Oxygen Oxygenic Photosynthesis Produces ATP and Reducing Power Prokaryotes Live in the Crust Crust Provides an Ecologic Niche Chemolithotrophs "Eat" Rock Origin of Life When Did Life Originate? When Did Earth Become Cool Enough for Life? Evidence for Early Life Precambrian Life Was Dominated by Stromatolites Building the Molecules of Life Where Did Prebiotic Synthesis Happen? Did Replication Precede Metabolism? Did Metabolism Emerge Before Replication? How Did Life Originate? What Were the First Organisms? What Was the Last Universal Common Ancestor? Hydrothermal Vents Are Prime Candidates for Genesis Early Life A Methane Greenhouse A Shift from CO2 to CH4 Greenhouse Happened in the Late Archaean An Organic Haze Would Form as CH4 Levels Rose The Great Oxidation Event The Oxygen Source Was Photosynthesis Evidence for the GOE is Geochemical Whiffs of Oxygen Preceded the GOE Glaciations Coincided with the GOE The "Boring Billion" O2 Levels Plummeted After the GOE The Canfield Ocean Is Anoxic and Sulfidic The Neoproterozoic Oxidation Event The Emergence of Life Methanogenesis and Sulfate Reduction Were Intertwined Nitrogen Fixation Probably Evolved Very Early Genome Expansion Occurred in the Archaean When Did Oxygenic Photosynthesis Start? Eukaryotes: Complex Life

Alan Longstaff originally trained as a biochemist and, after a senior lectureship in the Biosciences Department at the University of Hertfordshire, he became a university student once again to study astronomy and planetary science. He now divides his time between teaching and writing. Since 2003, he has worked part-time as an astronomy tutor and planetarium presenter for The Royal Observatory, Greenwich, and held part-time teaching posts at Queen Mary University of London, Waldegrave Science School for Girls, and the Open University. He has lectured to astronomical and geological societies, co/authored several textbooks, and is a regular contributor to Astronomy Now.