Astrobiology: an introduction
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| Language: | English |
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Boca Raton [u.a.]
CRC Press
2015
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| Series: | Series in astronomy and astrophysics
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| Physical Description: | XXXII, 422 S. Ill., graph. Darst. |
| ISBN: | 9781439875766 1439875766 |
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| 245 | 1 | 0 | |a Astrobiology |b an introduction |c Alan Longstaff |
| 264 | 1 | |a Boca Raton [u.a.] |b CRC Press |c 2015 | |
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| adam_text | Physics
Series in Astronomy and Astrophysics
Series Editors: M Birkinshaw, J Silk, and G Fuller
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.
Contents
o
yi
Constants.................................................................xxV
Acknowledgments.........................................................xxvii
Author...................................................................xxix
introduction.............................................................xxxi
1. Origin of the Elements.................................................1
1.1 Elements for Life.................................................1
1.2 The Universe Started from a Hot and Dense State...................1
1.2.1 Abundances of Primordial Elements Are Predicted by the
Big Bang Hypothesis......................................1
1.2.1.1 The Early Universe Was Dominated
by Radiation....................................1
1.2.1.2 Primordial Hydrogen and Helium Were
Synthesized in the First 20 min.................2
1.2.1.3 Lithium Abundance Is Problematic................4
1.3 The Message of Light..............................................4
1.3. 1 Atoms and Molecules Process Electromagnetic Radiation....4
1.3.2 Electronic Transitions Are Quantized.....................6
1.3.3 Energy Levels Govern Electronic Transitions in the
Hydrogen Atom............................................8
1.3.4 Spectrographs Are Used to Capture Spectra...............11
1.3.5 Stellar Spectra Encode Temperature and Elemental
Abundances..............................................11
1.3.5.1 Harvard Spectral Classification Is Based on the
Strength of Absorption Lines...................12
1.3.5.2 Luminosity Classes Are Based on the Sizes of
Stars..........................................14
1.3.5.3 A Plot of Luminosity against Temperature Is
a Hertzsprung-Russell Diagram..................15
1.4 Stellar Evolution................................................16
1.4.1 The Properties of Main Sequence Stars Are Determined
by Their Masses.........................................17
1.4.1.1 Brown Dwarfs Are Not Massive Enough to
Become Stars...................................18
1.4.1.2 The Boundary between Brown Dwarf and
Planet Is Hard to Define.......................18
1.4.1.3 The Upper Limit for Stellar Masses Is Not Well
Defined........................................19
1.4.2 Stars Form by the Collapse of Giant Molecular Clouds....19
1.4.2.1 Cloud Collapse Can Be Modeled
by Simple Physics..............................20
V
VI
Contents
1.4.2.2 Any Plausible Model of Star Formation Must
Be Able to Explain Several Key Facts...........21
1.4.2.3 Fragmentation and Accretion Are Key
Processes in Star Formation....................21
1.4.3 Protostars Contract Down Onto the Main Sequence..........22
1.4.3.1 Initial Protostar Contraction Is Isothermal.....22
1.4.3.2 Contraction onto the Main Sequence..............22
1.4.4 Main Sequence Stars Fuse Hydrogen to Helium.............22
1.4.4.1 Proton-Proton (PP) Chains Are the Main
Energy Yielding Fusion Reactions in Main
Sequence Stars..................................23
1.4.4.2 Stars Process y Radiation to Lower Energy
Radiation.......................................24
1.4.5 Many Low Mass Stars Become Red Giants...................24
1.4.5.1 Hydrogen Fusion Moves from Core to Shell........24
1.4.5.2 Core Fusion Reactions Generate Carbon and
Oxygen in Red Giant Stars.......................25
1.4.5.3 Asymptotic Giant Branch (AGB) Stars Build
Elements by Slow Neutron Capture................26
1.4.5.4 AGB Stars Distribute Metals into the
Interstellar Medium.............................27
1.4.5.5 Very Low Mass Stars Do Not Alter the
Interstellar Medium.............................27
1.4.6 High Mass Stars Make High Mass Elements..................28
1.4.6.1 Red Supergiants Can Forge Elements up to Iron..28
1.4.6.2 Core Collapse Supernovae Forms r-Process
Elements........................................29
1.4.6.3 Supernova Remnants Seed the Interstellar
Medium with Elements............................31
2. The Chemistry of Space...............................33
2.1 From Elements to Molecules...........................33
2.2 Astrochemical Environments......................................33
2.2.1 Cool Stars Have Molecular Absorption Lines...............33
2.2.2 The Interstellar Medium Is Extremely Tenuous.............33
2.2.2.1 Warm-Hot ISM Pervades Most of the Space
between the Stars...............................34
2.2.2.2 Atomic and Molecular Hydrogen Dominates
Diffuse and Dense Clouds........................35
2.2.3 The ISM Contains Dust Grains.............................37
2.2.4 AGB Stars Have Either Oxygen- or Carbon-Rich
Atmospheres..............................................39
2.2.4.1 Fusion Products Are Convected into the
Atmospheres of AGB Stars........................39
2.2.4.2 C/O Ratio Is the Key to Stellar Chemistry.......39
2.2.5 Doing Chemistry in Space.................................40
2.2.5.1 Astrochemistry Happens Over a Wide
Temperature Range...............................40
Contents vii
2.2.5.2 Astrochemistry Happens at Extraordinarily
Low Densities...................................41
2.2.5.3 Reaction Rate Constants Describe
Reaction Rates..................................41
2.2.6 Different Chemistry Operates in Dense Clouds and
Diffuse Clouds...........................................43
2.2.6.1 Dense Clouds Provide Safe Haven
for Molecules...................................43
2.3 Molecular Spectroscopy...........................................44
2.3.1 Molecules Are Detected Mostly by Vibrational and
Rotational Spectra.......................................44
2.3.1.1 Molecular Vibrations Are Quantized..............44
2.3.1.2 Molecules Are Similar to Springs................44
2.3.1.3 Not All Vibrations Are Infrared Active..........46
2.3.1.4 Molecular Rotations Are Quantized...............47
2.3.1.5 Rotational—Vibrational Spectra..................48
2.3.1.6 Isotopes Can Be Distinguished by
Rotational Spectra..............................50
2.3.1.7 Temperature Can Be Deduced from
Rotational Spectra..............................50
2.3.1.8 Polyatomic Molecules............................50
2.3.1.9 Electronic States of Molecules..................50
2.4 Building Molecules...............................................51
2.4.1 Molecules in the ISM.....................................51
2-4.2 Reaction Mechanisms....................................51
2.4.2.1 Ionization......................................51
2.4.2.2 Atomic Photoionization..........................51
2.4.2.3 Molecular Photoionization.......................52
2.4.2.4 Cosmic Ray Ionization...........................52
2.4.2.5 Photodissociation...............................52
2.4.2.6 Dissociative Recombination......................53
2.4.2.7 Dissociative Recombination of Molecules Is
Fast and Common.................................53
2.4.2.8 Neutral Chemistry...............................53
2.4.2.9 Ion—Molecule Reactions..........................54
2.5 Chemical Networks............*.....*............................54
2.5.1 Dust Grain Surfaces Catalyze Synthesis of
Hydrogen Molecules.......................................54
2.5.1.1 Molecular Hydrogen Is Protected by
Self-Shielding..................................55
2.5.1.2 Grain Surfaces Are Important for Oxygen
Chemistry.......................................56
2.5.1.3 Methanol Synthesis Involves Grain Surfaces......56
2.5.1.4 Diffuse Clouds Are Photon-Dominated Regions....56
2.5.1.5 X-Ray֊Dominated Regions.........................57
2.5.1.6 H3 Is the Starting Point for a Great Deal of
Chemistry.......................................58
2.5.1.7 Hydrocarbon Synthesis from H^ Gives Methane....59
viii
Contents
2.5.1.8 The C+ Ion Is a Starting Point for
PDR Chemistry....................................59
2.5.1.9 Nitrogen Chemistry Yields Ammonia................60
2.5.2 Chemical Species Can Trace ISM Conditions
and Processes.............................................60
2.5.2.1 CN, HCN, and NHC Are Intimately Related..........60
2.5.2.2 HCN and Friends Provide Clues to the State
of the ISM..................................... 61
3. Habitable Earth..........................................................63
3.1 Earth in Context.................................................63
3.1.1 There Are Eight Major Planets.............................63
3.1.1.1 Terrestrial Planets Have Low Masses..............63
3.1.1.2 Gas and Ice Giants Have High Masses..............63
3.1.1.3 Most Planets Have Moons..........................64
3.1.1.4 Many Solar System Bodies Are Differentiated......65
3.1.2 The Planets Were Condensed from a Spinning Disc..........65
3.1.3 The Solar System Contains Numerous Small Bodies..........65
3.1.3.1 The Scattered Kuiper Belt Is the Source of
Jupiter Family Short-Period Comets...............66
3.1.3.2 The Oort Cloud Is the Source of Halley Family
Short-Period and Long-Period Comets..............66
3.1.3.3 Asteroids Sample Very Early Solar System
Material.........................................67
3.1.4 What Is a Planet?.........................................67
3.1.4.1 A Planet Must Satisfy Three Criteria.............67
3.2 Habitability Is an Attribute of the Entire Earth System...........68
3.2.1 The Structure and Composition of the Solid Earth..........68
3.2.2 The Chondritic Earth Model Provides a First
Approximation to Its Bulk Composition.....................68
3.2.3 Seismology Provides a Picture of the Earth’s Interior.....69
3.3 What Makes Earth Habitable?.......................................70
3.3.1 Temperature at the Earth’s Surface Is Largely
Determined by the Sun.....................................71
3.3.2 Liquid Water Exists on the Earth’s Surface.............. 72
3.3.3 Earth Is in a Stable Orbit in the Habitable Zone..........73
3.3.3.1 The Inner Edge of the Habitable Zone Is
Defined by the Moist Greenhouse Effect...........74
3.3.3.2 The Outer Boundary of the Habitable Zone Is
Defined by Maximum C02 Greenhouse................75
3.3.3.3 The Habitable Zone Changes with Time............75
3.3.3.4 Habitable Zones Are Defined for Exoplanet
Systems..........................................75
3.3.4 Earth’s Dense Atmosphere Contributes to Habitability......76
3.3.4.1 A Planet’s Mass Determines What Gases It
Can Retain.......................................76
3.3.5 A Global Magnetic Field May Be Required
for Habitability..........................................80
Contents Іх
3.3.5.1 Earth’s Magnetic Field Helps It Retain Its
Atmosphere.....................................80
3.3.5.2 Earth’s Atmosphere Has Been Shielded by a
Magnetic Field for at Least 3 Gyr.............81
3.3.5.3 Mars Lacks a Magnetic Field and Has Lost
Much of Its Atmosphere.........................81
3.3.5.4 Venus Lacks a Magnetic Field yet Has a
Dense Atmosphere...............................81
3.3.5.5 A Global Magnetic Field Requires
a Liquid Core..................................81
3.3.5.6 The Core Has a Light Element That Is Crucial
for the Geodynamo..............................82
3.3.5.7 Why do Mars and Venus Lack Magnetic Fields?...82
3.4 Earth Seems Unique in Having Plate Tectonics...................83
3.4.1 Plate Tectonics Depends on a Weak Mantle Layer.........83
3.4.2 New Ocean Crust Is Made at Constructive
Plate Boundaries........................................84
3.4.3 Ocean Crust Is Destroyed at Destructive
Plate Boundaries........................................84
3.4.4 Hot Spot Volcanism: Evidence for Mantle Convection?.....85
3.4.5 Plate Tectonics Is Self-Regulating......................85
3.4.5.1 The Carbonate-Silicate Cycle Is a Planetary
Thermostat................................... 86
3.4.5.2 Silicate Weathering Reduces Atmospheric C02....87
3.4.5.3 Subduction Volcanism Increases
Atmospheric C02................................88
3.4.5.4 The Carbonate—Silicate Cycle Regulates
Temperature by Negative Feedback...............88
3.4.6 Plate Tectonics May Be Required for Habitability........89
3.4.7 Plate Tectonics Seems Not to Operate on Mars or Venus...89
4. Building the Solar System............................................91
4.1 Planet Formation Is Contingent.................................91
4.2 Planets Formed by Accretion from the Solar Nebula..............91
4.2.1 The Solar Nebula Was a Dynamic Environment..............91
4.2.2 The Solar Nebula Formed a Spinning Disc.................92
4.2.3 Planet and Star Formation Occur Together................92
4.2.4 Condensation of Solids from the Solar Nebula Depended
on Temperature..........................................93
4.2.4.1 The First Solids Condensed in the Solar Nebula
4.567 Gyr ago....................-............95
4.2.5 Accretion Involves Several Distinct Mechanisms..........95
4.2.5.1 Cohesion Builds Particles a Few Millimeters
in Size........................................95
4.2.5.2 Chondrules Formed in Episodes of
Intense Heating................................95
4.2.5.3 Assembly of Planetesimals Is
Poorly Understood..............................98
X
Contents
4.2.5.4 Runaway Growth Builds Oligarchs and
Planetary Embryos..............................98
4.2.5.5 Debris Discs Result from End Stages of Planet
Building........................................99
4.2.6 Heat Sources Drive Differentiation........................99
4.2.6.1 Vesta Is an Ancient Differentiated World.......100
4.2.7 Differentiation Redistributes Elements...................100
4.2.7.1 Elements Have Distinct Chemical Affinities.....100
4.2.8 Gas Giants Must Have Assembled Within a Few Million
Years................................................... 101
4.2.9 Accretion of Terrestrial Planets Took Tens of Millions of
Years....................................................102
4.3 The Solar System Started with a Bang............................102
4.3.1 26Mg Traces the Original 26A1............................102
4.3.2 Did the Decay of 26A1 Make Life on Earth Possible?.......103
4.4 Dating Events in the Early Solar System Relies on Radioactive
Isotopes.........................................................104
4.4.1 Radiometric Dating Relies on the Exponential Decay
of Radioisotopes.........................................104
4.4.2 Radiometric Dating Uses Isochron Plots...................105
4.5 Planetary Migration Is Required to Resolve Several Paradoxes....107
4.5.1 Theories of Planetary Migration Have Been Derived........107
4.5.1.1 Planets Embedded in a Gas Disc Experience
Type I Migration...............................108
4.5.1.2 Planets in Gaps Experience Type II Migration...108
4.5.1.3 Halting Migration..............................108
4.5.1.4 Gravitational Scattering.......................108
4.5.2 Some Features of Solar System Architecture Have Been
Hard to Explain..........................................109
4.5.2.1 The Late Heavy Bombardment (LHB) Is One
Model of Impact History........................109
4.5.3 The Nice Model Accounts for Solar System Architecture
by Planetary Migration.................................. 111
4.5.3.1 Simulating the Early Solar System............. Ill
4.5.3.2 The Original Nice Model Explains the
Eccentricities of the Giants.................. ill
4.5.3.3 The Nice Model Has an Explanation for the
Late Heavy Bombardment........................ 112
4.5.3.4 The Main Asteroid Belt May Provide Clues
to the Origin of the LHB...................... 112
4.5.3.5 The Grand Tack Accounts for the Inner Solar
System........................................ 115
5. Early Earth........................................................... 117
5.1 Assembly of the Earth Can Be Modeled........................... 117
5.1.1 To First Approximation Earth Grew at a Decreasing
Exponential Rate........................................ 117
5.1.2 Accretion Was Probably Heterogeneous.................... 117
C ontents xi
5.2 Early liarth Was Shaped by a Moon-Forming Impact.............. 117
5.2.1 The Moon-Forming Impact is Supported by Theory
and Cicochcmistry....................................... 1 IK
5.2.). 1 C omputcr Simulations Show a Moon-Forming
Impact Is Dynamically Feasible............... 1 IS
5.2.1.2 Much of Theia s Core Becomes Part of Earth s
Core ....................................... 119
5.2.1.3 Lunar Rocks Arc Depleted in Volatiles........ I 19
5.2.1.4 Harth and Moon Have the Same Oxygen and
Silicon Isotopes............................ 120
5.2.1.5 The Moon May Have Originated from the
Harth s Mantle after If Had Already Produced a
Crust ....................................... 121
5.2.1.6 Changing Model Parameters Can Achieve
Similar Isotopic Compositions for the Harth
and Moon..................................... 121
5.2.1.7 There Arc Difficulties with the Giant Impact
Theory....................................... 122
5.2.2 The Timing of the Moon-Forming Impact Is Poorly
Constrained............................................ 1 22
5.2.3 Tidal Forces Drove Evolution of the Earth-Moon System. 122
5.3 The Early Hadean Was Hot......................................1 23
5.3.1 Earth s Postimpact Atmosphere Was Largely
Rock Vapor............................................ 123
5.3.2 A Magma Ocean Remained After the Moon-Forming
Impact ................................................1 24
5.3.3 The Hadean Mantle. Atmosphere, and Oceans Could
Have Coevolved ....................................... 124
5.3.3.1 Early Hadean Earth Experienced a Runaway
Greenhouse...................................125
5.3.3.2 CO; Must Have Been Removed from the
Atmosphere................................. 126
5.3.4 A Dry Accreting E arth Would Be Hot During
the Hadean ............................................ 1 26
5.4 Late Events Modified the Composition of the Earth............. 127
5.4 1 Earth s Mantle and Cru^t Has an Excess of Sidcrophiic
Elements............................................. 1 27
5.4.2 Core Separation Happened at High Pressure
and Temperature ...................................... 127
5.4.3 Siderophtlc Elements Were Likely Delivered by a
Late Veneer.......................................... 1 28
5.4.4 The Mantle Has Become More Oxidized with Time.........128
5.4.4.1 Degassing Oxidized the Upper Mantle......... 129
5.4.4.2 Large Terrestrial Planets Self-Oxidizc...... 129
5.5 How Did the Terrestrial Planets Acquire Water?................130
5.5.1 The Water Inventory of the Earth Is Not Well Know n...130
5.5.2 Did Terrestrial Planets Accrete Dry?..................130
5.5.3 Did Terrestrial Planets Accrete Wet?................. 131
Xll
Contents
5.53 A Formation of Hydrated Minerals In Situ Is
Unlikely......................................131
5.53.2 Influx of Wet Planetesimals Could Have Been
Responsible for Wet Accretion.................132
5.5.4 Volatile Delivery Could Have Occurred Late.............133
5.5.4.1 Comets Are a Potential Source of Water.........134
5.5.4.2 Asteroids Are a Potential Source of Water.....134
5.5.4.3 Water Delivery May Have Been Stochastic.......135
5.6 The Temperature of the Late Hadean and Archaean Are Not
Well Constrained...............................................135
5.6.1 Geological Clues Suggest Early Earth Was Warm
Rather Than Hot.........................................135
5.6.2 When Did the First Oceans Form?.........................137
5.6.2.1 Do Zircons Provide Evidence for Oceans
by 4.4 Gyr?...................................137
5.6.2.2 Water-Lain Sediments Are Found at
3.85 Gyr......................................138
5.6.2.3 Evidence for Hydrothermal Activity Is Not
Evidence for Oceans...........................138
5.7 Plate Tectonics on Early Earth.................................139
5.7.1 When Did Plate Tectonics Start on Earth?................139
5.7.2 Plate Tectonics May Not Have Operated in the Hadean....139
5.7.2.1 High Resurfacing in the Hadean May Have
Led to Efficient Cooling......................140
5.7.3 What Was the Nature of Early Plate Tectonics?...........140
5.7.3.1 Most Continental Crust Formed
in the Archaean.............................. 141
5.7.3.2 The Style of Plate Tectonics Changed
3 Gyr Ago.....................................142
5.733 Vertical Tectonics May Have Generated the
First Continental Crust.......................142
5.8 Earth’s Atmosphere Has Changed Over Time.......................143
5.8.1 Earth’s Atmosphere May Come from Two Sources............143
5.8.2 The Oxidation State of The Atmosphere Has Altered.......144
5.8.3 Nitrogen May Be Derived from Ammonia....................144
5.8.4 The Faint Young Sun Paradox.............................146
5.8.4.1 Lower Albedo Is a Controversial Solution to
the Faint Young Sun Paradox.................. 147
5.8.4.2 Higher Amounts of Greenhouse Gases Could
Solve the Faint Young Sun Paradox.............147
5.8.4.3 The Pressure of the Earth’s Atmosphere
Was Less Than Twice Its Present Value
2.7 Gyr Ago...................................150
5.8.4.4 Carbon Dioxide Cannot Have Been Greater
Than 0.03 Bar in the Late Archaean
Atmosphere....................................152
5.8.4.5 Model Late Archaean Atmospheres Can Keep
Earth Warm....................................152
Contents xiii
5.8.4.6 There Are Several Abiotic Sources for
Atmospheric Methane............................154
5.8.4.7 Is Abiotic Methane Sufficient to Solve the
Faint Young Sun Paradox?.......................154
6. Properties of Life....................................................157
6.1 Can Life Be Defined?...........................................157
6.1.1 Life Is a Complex, Self-Organi zing, Adaptive Chemical
System..................................................157
6.1.1.1 Complexity in Living Systems Is Hard
to Define......................................157
6.1.1.2 Living Systems Have Emergent Properties........157
6.1.2 The Chemistry of Life Is Far from Equilibrium..........158
6.1.2.1 When Will a Reaction Happen Spontaneously?....159
6.1.2.2 Life Obeys the Second Law of
Thermodynamics................................ 161
6.1.2.3 Life Messes Up Its Environment................ 161
6.1.3 Life Requires an Energy Source......................... 162
6.1.3.1 Solar Radiation Can Be Harnessed Directly
by Photosynthesis............................. 162
6.1.3.2 Organic Carbon Is Oxidized in Respiration......164
6.1.3.3 Redox Reactions Are Coupled Reduction-
Oxidation Reactions............................165
6.1.3.4 Redox Reactions Are Quantified by Redox
Potentials.....................................165
6.1.3.5 Are Redox Mechanisms a Universal Attribute
for Life?......................................167
6.1.4 Living Systems Are Capable of Self-Replication......... 167
6.1.5 Life Exhibits Darwinian Evolution.......................167
6.1.5.1 Evolution Has No Goal..........................168
6.1.5.2 Complexity of Living Systems Tends to
Increase with Time.............................168
6.1.5.3 Is Darwinian Evolution Universal to Life
Everywhere?....................................169
6.1.6 How Useful Are These Criteria for Detecting Life?......169
6.2 Are There Universal Chemical Requirements for All Life?.........169
6.2.1 No Element Is More Versatile in Its Chemistry
Than Carbon.............................................169
6.2.1.1 Carbon Is Tetravalent......................... 170
6.2.1.2 Carbon Has a Moderate Electronegativity........170
6.2.1.3 Can Silicon Substitute for Carbon in
Biochemistry?................................. 171
6.2.2 Water As a Universal Solvent............................171
6.2.2.1 Alternative Solvents Have Been Postulated..... 172
7. Terrestrial Biochemistry............................................. 175
7.1 Building Blocks for Life....................................... 175
7.1.1 Polymeric Macromolecules............................... 175
XIV
Contents
7.1.1.1 Polypeptides Are Polymers of Amino Acids....... 175
7.1.1.2 Nucleic Acids Are Informational
Macro molecules.............................. 177
7.1.1.3 Polysaccharides Are Polymers of Sugars.........179
7.1.1.4 Lipids.........................................179
7.2 All Life on Earth Consists of Cells.............................182
7.2.1 Information Flow in Cells...............................182
7.2.1.1 Genes Have Several Components..................183
7.2.2 All Life on Earth Has One of Two Basic
Cell Architectures......................................184
7.2.2.1 Prokaryotes Have Simpler Genomes than
Eukaryotes.....................................184
1.2.2.2 Eukaryotes Have Mitochondria and
Chloroplasts...................................185
7.2.2.3 All Cells Have Internal Scaffolding............185
7.2.2.4 Almost All Organisms on Earth
Are Prokaryotes................................185
7.2.3 Gene Transfer Can Occur Vertically or Horizontally......186
7.2.4 All Life on Earth Falls into Three Domains..............186
7.3 DNA Is the Universal Replicator.................................188
7.3.1 All Life on Earth Uses DNA..............................188
7.3.2 DNA Replication Was Deduced from Theory.................188
7.3.3 DNA Acts as a Template..................................189
7.3.3.1 DNA Replication Is Fast........................189
7.3.3.2 DNA Replication Requires Catalysts.............191
7.3.3.3 DNA Replication Is High Fidelity...............191
7.3.3.4 DNA Mutations Are the Source of Variation......191
7.3.3.5 The Genetic Code Shows a Single Origin of
All Life.......................................191
7.3.3.6 The Genetic Code Provides Clues to
Its Origin.....................................192
7.4 Metabolism Matches Lifestyle....................................193
7.4.1 Living Systems Enhance Reaction Kinetics................194
7.4.2 Life on Earth Has Three Metabolic Requirements..........195
7.4.2.1 Organisms Can Be Categorized
by Metabolism................................ 195
7.5 Cells Harness Free Energy.......................................196
7.5.1 Respiration Requires an Exogenous Electron Acceptor.....196
7.5.2 Most Carbon Oxidation Happens in the Krebs Cycle........196
7.5.3 Electron Chains “Quantize” Free Energy Availability.....198
7.5.4 AG° of Redox Reactions Can Be Calculated...............198
7.5.4.1 Exergonic Reactions Have Positive A££..........198
7.5.5 Proton Gradients Are the Core of Terrestrial
Metabolism..............................................200
7.5.5.1 Prokaryotes Pump Proteins Across Their Cell
Membrane.......................................200
7.5.5.2 Eukaryotes Make ATP in Mitochondria............200
7.5.5.3 Electron Transport Uses Metal Ions.............202
Contents
XV
7.5.6 Anerobic Respiration Uses Electron Acceptors Other
Than Oxygen...........................................202
7.5.7 Fermentation Uses an Endogenous Electron Acceptor......204
7.6 Phototrophs Harvest Sunlight...................................205
7.6.1 Not All Photosynthesis Produces Oxygen.................205
7.6.2 Oxygenic Photosynthesis Produces ATP and Reducing
Power.................................................205
7.7 Prokaryotes Live in the Crust..................................206
7.7.1 Crust Provides an Ecologic Niche.......................206
7.7.2 Chemolithotrophs “Eat” Rock............................207
8. Origin of Life.....................................................
8.1 When Did Life Originate?....................................
811 When Did Earth Become Cool Enough for Life?.............
8.1.2 Evidence for Early Life.............................
8.1.2.1 Do Light Carbon Isotopes Hint at First Life?..
8.1.2.2 Fossils or Artifacts?......................
8.1.3 Precambrian Life Was Dominated by Stromatolites.....
8.2 Building the Molecules of Life..............................
8.2.1 where Did Prebiotic Synthesis Happen?...............
8.2.LI Urey-Miller Experiments Have a Fatal Flaw..
8.2.1.2 Carbonaceous Chondrites Are Rich
in Organics...............................
8.2.1.3 Most Organic Carbon in Meteorites and
Comets Is Unavailable.....................
8.2.2 Did Replication Precede Metabolism?.................
8.2.2.1 Did Life Begin with a Self-Copying
Molecule?.................................
8.2.2.2 Ribozymes Support an RNA World.............
8.2.2.3 Evidence for the RNA World.................
8.2.2.4 Making Ribonucleosides Is a Problem........
8.2.2.5 Pyrimidine Ribonucleotide Synthesis Can
Happen Under Prebiotic Conditions.........
8.2.2.6 Abiotic Synthesis of Self-Replicating RNA
Is a Problem..............................
8.2.2.7 Was There a Pre-RNA Replicator?............
8.2.2.8 Why the RNA World Idea Might Be Wrong...
g ^ Did Metabolism Emerge Before Replication?...........
How Did Life Originate?.....................................
* What Were the First Organisms?........................
•3.2 What Was the Last Universal Common Ancestor?..........
8.3.2.1 LUCA Lacked Several Traits.................
8.3.2.2 LUCA Was a Hyperthermophile................
^ Hydrothermal Vents Are Prime Candidates for Genesis.
8.3.3.1 Black Smokers Are Acidic
Hydrothermal Vents........................
8.3.3.2 Acidic Vents Were Initially Proposed for
Life’s Origin.............................
209
209
209
209
210
212
212
214
214
215
216
217
218
218
218
219
220
220
220
221
222
223
223
224
224
225
225
225
226
226
XVI
Contents
8.3.3.3 Alkaline Vents Are More Favorable Cradles
Than Acidic Vents..............................227
8.3.3.4 Serpentinization Makes Hydrogen
and Methane....................................228
8.3.3.5 Alkaline Vents Can Provide Energy for Life....229
8.3.3.6 Did the First Metabolic Pathway Reduce C02
with H2 to Produce Acetate?....................229
8.3.3.7 Alkaline Vents Have Proton Gradients...........231
8.3.3.8 Did the First Pathway Make
Acetyl Phosphate?..............................231
8.3.3.9 Temperature Gradients Encourage
Polymerization................................232
8.3.3.10 DNA, RNA, and Proteins Evolved in the Vent....232
9. Early Life............................................................235
9.1 A Methane Greenhouse............................................235
9.1.1 A Shift from C02 to CH4 Greenhouse Happened
in the Late Archaean.................................. 235
9.1.2 An Organic Haze Would Form as CH4 Levels Rose...........235
9.2 The Great Oxidation Event.......................................236
9.2.1 The Oxygen Source Was Photosynthesis....................236
9.2.2 Evidence for the GOE is Geochemical.....................237
9.2.2.1 Sulfur Isotopes Time the GOE...................237
9.2.2.2 Banded Iron Formations: A Red Herring? ........238
9.2.3 Whiffs of Oxygen Preceded the GOE.......................240
9.2.4 Glaciations Coincided with the GOE......................240
9.3 The “Boring Billion”............................................240
9.3.1 02 Levels Plummeted After the GOE.......................241
9.3.2 The Canfield Ocean Is Anoxic and Sulfidic...............241
9.3.2.1 Euxinia Locks Up Essential Trace Metals.......243
9.3.3 The Neoproterozoic Oxidation Event......................243
9.3.3.1 Oxidation Produced Glaciation..................243
9.3.3.2 Continent Configuration Contributed to
the Freeze.....................................243
9.4 The Emergence of Life...........................................244
9.4.1 Methanogenesis and Sulfate Reduction
Were Intertwined........................................244
9.4.2 Nitrogen Fixation Probably Evolved Very Early...........244
9.4.3 Genome Expansion Occurred in the Archaean...............245
9.4.4 When Did Oxygenic Photosynthesis Start?.................246
9.4.4.1 Anoxygenic Photosynthesis Evolved First........246
9.4.4.2 12C, BIFs, and Cyanobacterial Biomarkers
Are Red Herrings...............................247
9.4.4.3 Did Oxygenic Photosynthesis Start
-2.4 Gyr ago?..................................247
9.5 Eukaryotes: Complex Life.......................................247
9.5.1 When Did Eukaryotes Appear?.............................247
9.5.2 Eukaryotes Are Archaeon—Bacteria Chimeras............. 248
Contents xvii
9.5.2.1 Endosymbiotic Origin for Eukaryotes Is a
Nineteenth Century Idea........................248
9.5.2.2 Eukarya Only Evolved Once......................248
9.5.3 The Hydrogen Hypothesis Explains Endosymbiosis.........249
9.5.3.1 Symbiosis Is a Two-Way Exchange................249
9.5.3.2 Symbiosis Had to Be Rapid......................251
9.5.3.3 Mitochondria Lost Genes to the Nucleus.........251
9.5.4 Eukaryotes Inherited Bacterial Lipids...................251
9.5.5 Eukaryotes Have Huge Advantages Over Prokaryotes.......251
9.5.5.1 Prokaryotes with Small Genomes Are Favored.....252
9.5.5.2 Small Is Best for Energy Efficiency............252
9.5.6 Mitochondria Are Advantageous for Energetics............252
9.5.6.1 Oxidative Phosphorylation Is Normally
Demand Led..................................253
9.5.6.2 Oxidative Phosphorylation Can Be Supply Led....253
9.5.7 Large Size Is Advantageous for Eukaryotes...............253
9.6 The Fate of Life on Earth.......................................254
9.6.1 Earth Will Be Habitable for Another 1.5 Billion Years..254
10. Mars...................................................................255
10.1 Martian Romance.................................................255
10.LI Mariner Missions Reveal a Cold Arid World................255
10.2 Martian Geology............................................... 255
10.2.1 Mars Is a Planetary Embryo..............................255
10.2.1.1 The Martian Core Is Totally or Partly Liquid..256
10.2.1.2 When Mars Lost Its Magnetic Field
Is Significant.................................256
10.2.2 Mars Has Two Very Different Hemispheres................257
10.2.2.1 The Origin of the Northern Lowlands Is
Uncertain......................................257
10.2.2.2 The Tharsis Bulge Is the Highest Region
on Mars........................................257
10.2.2.3 Cratering Rates Provide Clues to
Mars’ History..................................259
10.2.3 Spectrometry Reveals the Nature of Planetary Surfaces..260
10.2.3.1 Gamma Ray Spectrometry (GRS)...................260
10.2.3.2 Alpha-Particle-X-Ray Spectrometry (APXS)......261
10.2.3.3 Thermal Emission Spectrometry (TES)............261
10.2.3.4 Reflectance Spectrometry.......................262
10.2.3.5 X-Ray Diffraction (XRD)........................262
10.2.4 The Martian Crust Is Mostly Basalt.....................263
10.2.4.1 Much of the Surface of Mars Is Covered by
Regolith.......................................264
10.3 Water Ice Is Abundant on Mars...................................264
10.3.1 Mars Has Substantial Frozen Water.......................264
10.3.1.1 Obliquity Swings Redistribute Water Ice........264
10.3.1.2 Subsurface Water Ice Is Revealed by
Geological Features
265
Contents
10.3.1.3 Subsurface Water Ice Has Been Detected by
Geophysics....................................265
10.3.1.4 Water Ice Has Been Seen Directly.............265
10.3.1.5 The Cryosphere Is a Thick Permafrost Layer...267
10.3.1.6 Extensive Groundwater Aquifers Are Missing...267
10.4 Water Has Flowed on Mars.......................................267
10.4.1 Mars Has Numerous Fluvial Features.....................268
10.4.1.1 Valley Networks Are Not Like Terrestrial River
Beds..........................................268
10.4.1.2 Outflow Channels Were Formed by Episodic
Floods........................................268
10.4.1.3 Did Early Mars Have a Northern Ocean?........269
10.4.1.4 Martian Gulleys Are Enigmatic................270
10.4.2 Mars Exploration Rovers Have Searched for Signs of
Liquid Water........................................ 270
10.4.2.1 Water Interaction at Gusev Has Been Limited..270
10.4.2.2 Meridiani Hosts Water-Formed Minerals........270
10.4.2.3 Was Meridiani Plain a Sulfate Brine Lake?....271
10.4.3 Global Geological Markers Can Reveal How Long Mars
Was Wet...............................................271
10.4.3.1 Lack of Carbonates Is a Red Herring..........272
10.4.3.2 The Martian Surface Has Not Suffered Much
Alteration by Water...........................272
10.4.3.3 Clays Provide Insight into Water Action......272
10.4.3.4 Martian Clays Are Generally Noachian.........272
10.4.3.5 Much Hydrothermal Activity Was Produced
by Impacts on Early Mars......................273
10.4.4 Mars Has Experienced Three Climates....................274
10.4.4.1 Clays Formed in the Phyllocian Era...........274
10.4.4.2 Sulfates Were Produced in the Theiikian Era..275
10.4.4.3 The Siderikan Era Made Mars Red..............275
10.5 Atmosphere.....................................................275
10.5.1 Liquid Water Cannot Exist at the Martian Surface Today.276
10.5.2 Detection of Methane in the Martian Atmosphere Is
Dubious...............................................276
10.5.3 Atmosphere of Early Mars...............................276
10.5.3.1 Mars Probably Lost Most of Its Water Early On.... 277
10.5.3.2 Mars Probably Lost Most of Its Atmosphere
Early On.................................. 277
10.5.3.3 Several Atmosphere Loss Mechanisms Likely
Operated on Mars..............................277
10.5.3.4 Impacts Can Remove Substantial Amounts of
Atmosphere.................................. 277
10.5.3.5 Sputtering Mass Fractionates Isotopes........278
10.5.3.6 What Was the Atmospheric Pressure of Early
Mars?.........................................279
10.5.3.7 Early Mars Probably Had a
Reduced Atmosphere............................280
Contents
XIX
10.5.3.8 Climate Models Struggle to Warm Early Mars.....280
10.5.3.9 Hydrogen Might “Rescue” a Warm Climate.........282
10.5.4 Was Mars Episodically Warm and Wet?.....................282
10.5.4.1 Can Impact Precipitation Account for the
Fluvial Features?.............................284
10.6 Mars and Life..................................................284
10.6.1 The Viking Experiments Were Designed to Detect Life.....284
10.6.1.1 Pyrolytic Release Tests for Carbon Fixation....284
10.6.1.2 Labeled Release (LR) Tests for Metabolism.......285
10.6.1.3 GCMS Detects Organic Compounds................285
10.6.1.4 What Was the Legacy of Viking?................285
10.6.2 Does ALH84001 Harbor Evidence of Life?..................286
10.6.2.1 ALH84001 Has Had a Shocking History...........286
10.6.2.2 Four Features Hinted at Relic Life............286
10.6.2.3 Complex Organic Molecules Were Detected.......286
10.6.2.4 Iron Sulfide (Fe(II)S) and Iron Oxides
Appeared Together.............................287
10.6.2.5 Magnetite Crystals Are Enigmatic............ 287
10.6.2.6 “Fossil Bacteria” Seem Too Small..............287
10.6.2.7 ALH84001 Does Not Provide Evidence
for Life......................................287
10.6.3 Martian Life Could Be Based on Iron and Sulfur
Metabolism..............................................287
10.6.3.1 Terrestrial Iron-Oxidizing Bacteria “Breathe”
Nitrate.......................................287
10.6.3.2 Mars Is Rich in Electron Acceptors for Fe-
and S-Reduction...............................288
11. Icy Worlds............................................................289
11.1 Life Might Exist Beyond the Conventional Habitable Zone........289
11.2 Titan..........................................................289
11.2.1 Titan Has a Dense Atmosphere............................290
11.2.1.1 A Methane Cycle Operates on Titan.............290
11.2.1.2 Titan Is an Ice-Silicate World................292
11.2.1.3 Titan Harbors a Subsurface Water Ocean........293
11.2.1.4 Ammonia Is an Anti-Freeze.....................294
1 1.2.2 Atmospheric Methane Must Be Continually Regenerated.....295
1 1.2.2.1 Subsurface Methane Reservoirs Must Exist......295
11.2.2.2 Why the Ocean Cannot Be the Source of
Atmospheric Methane...........................296
11.2.2.3 Cryovolcanism.................................296
11.2.3 Organic Chemistry Occurs in Titan’s Atmosphere..........297
11.2.3.1 Low Temperatures Make for Slow Kinetics.......297
11.2.3.2 Free Radical and Ion-Neutral Chemistry
Dominates.....................................298
11.2.3.3 Methane Is the Precursor Hydrocarbon .........299
11.2.3.4 Nitrogen Leads to Nitriles....................300
11.2.3.5 Tholins Are Formed by Ion-Neutral Reactions...300
XX
Contents
11.2.3.6 Titan Chemistry Is Being Explored in the
Laboratory...................................301
11.2.4 Could There Be Life on Titan?..........................301
11.2.4.1 Is the Subsurface Ocean Habitable?............301
11.2.4.2 Terrestrial-Style Methanogenesis Is Dubious...302
11.2.4.3 Titan’s Atmosphere Poses Paradoxes............302
11.3 Enceladus......................................................303
11.3.1 Enceladus Has Been Resurfaced Multiple Times............304
11.3.2 Enceladus Cryovolcanic Plumes Contain Water Vapor.......304
11.3.3 What Heats Enceladus Now?.............................306
11.3.3.1 Tidal Stresses Control Eruptions..............307
11.3.3.2 Cryovolcanism Is Probably Driven by
Ammonia-Water Magma..........................308
11.3.3.3 Putative Organisms Are Water-Based...........308
11.4 Europa.........................................................308
11.4.1 Europa Is a Differentiated World......................309
11.4.2 There Is Good Evidence for a Europan Ocean............310
11.4.3 How Thick Is the Europan Crust?.......................310
11.4.3.1 Europa Experiences Tidal Heating.............311
11.4.3.2 Crustal Thickness Can Be Estimated from
Mechanical Properties...................... 312
11.4.3.3 Surface Features Are Evidence for an Ocean....312
11.4.3.4 Chaos Terrain Implies a Thin Crust...........312
11.4.3.5 Water-Ice Cryovolcanism May Occur
on Europa....................................313
11.4.4 The Europan Surface Is Chemically Altered.............313
11.4.4.1 Europa’s Surface Is Altered by Radiolysis....314
11.4.4.2 The Europan Ocean May Resemble Earth’s
Oceans.......................................315
11.4.4.3 Low Hydrogen Peroxide Abundance
May Limit Oxidation of the Ocean.............316
11.4.4.4 How Effectively Do the Surface and Ocean
Communicate?.................................316
11.4.5 What Is the Astrobiologie al Potential of Europa?.....317
11.4.5.1 A Reducing Ocean Would Be a
Sink for Oxidants............................317
11.4.5.2 Could H202 Support Biology?..................318
11.4.5.3 Energy for Hydrothermal Vents................318
11.4.5.4 What Is the Oxidation State of the Europa
Mantle?......................................319
12. Detecting Exoplanets.................................................321
12.1 Exoplanet Bonanza..............................................321
12.1.1 The First Exoplanets Were Found by Timing Pulsars.....321
12.1.2 The First Exoplanet Around a Main Sequence Star
Was Discovered in 1995................................321
12.2 Some Exoplanets Can Be Imaged Directly.........................322
12.2.1 Planets Are Extremely Dim Compared to Their Host Stars.322
Contents xxi
12.2.2 Coronagraphs Create Artificial Hclipscs.................323
12.2.3 Nulling Interferometry Cuts Out Starlight...............323
12.2.4 Direct Imaging Reveals High Mass Planets................323
12.3 Astrometry Detects Binary Systems by Stellar ‘Wobble”..........324
12.4 The Radial Velocity Method Uses the Doppler Effect..............325
12.4.1 Defining the Radial Velocity............................326
12.4.1.1 Determining Radial Velocity Is a Challenge.....326
12.4.1.2 RV Calculations Must Sidestep the Unknown
Inclination...................................326
12.4.2 Finding the Period and Semi-Major Axis of an
Exoplanet s Orbit.......................................327
12.4.3 The RV Method Provides a Lower Bound on
Planetary Mass..........................................328
12.4.4 The RV Method Is Biased to Detect Massive Planets
with Short Periods......................................329
12.5 Exoplanets Are Revealed When They Transit Their Star............331
12.5.1 Exoplanet Transits Dim Starlight........................331
12.5.2 The Transit Method Allows Several Parameters to Be
Deduced.................................................333
12.5.2.1 The Period Gives the Semi-Major Axis of the
Exoplanet’s Orbit.............................333
12.5.2.2 Transits Allow Mass to Be Refined..............334
12.5.2.3 Exoplanet Radius. Volume, and Bulk Density
Can Be Found..................................336
12.5.2.4 Exoplanetary Temperature and Atmosphere
Composition May Be Revealed ................ 336
12.5.2.5 Exoplanet Albedo Can Be Estimated..............336
12.5.2.6 False Positives Arise with the Transit Method..336
12.5.3 Transit Timing Variation Uncovers Multiple and
Circumbinary Exoplanets.................................337
12.5.4 Transits Can Potentially Detect Earth-Mass Planets......337
12.5.5 Most Transit Detections Have Been Made from Space.......338
12.5.5.1 Kepler Had 961 Confirmed Exoplanets
by April 2014.................................338
12.6 Gravitational Tensing Can Unveil Exoplanets.....................339
12.6.1 Gravitational Microlensing Events Are Short-Lived.......339
12.6.2 Microlensing Yields Information About
Exoplanet Systems.......................................339
12.6.3 There Are Both Pros and Cons to Lensing.................341
12.7 Detection Methods Are Biased.....................................341
12.7.1 Survey Statistics Can Estimate What We
Cannot Detect...........................................342
13. Exoplanetary Systems.................................................343
13.1 Surveys Probe Exoplanet Properties....................343
13.1.1 Exoplanet Diversity Is Large............................343
13.1.2 Exoplanets Are Classified According to Their Size.......343
13.1.3 Hot Jupiters Were Discovered Early......................345
XXII
Contents
13.1.4 Small Exoplanets Are Commonest...........................345
13.1.4.1 The Planet/Star Ratio Is of Order One..........346
13.1.5 Exoplanet Composition Can Sometimes Be Deduced...........346
13.1.5.1 Compositions Can Be Plotted on a Ternary
Diagram.........................................346
13.1.5.2 Protoplanets with Mass Greater than 1.5Me
May Become Mini-Neptunes........................348
13.1.5.3 Could Water Worlds Exist?......................349
13.1.5.4 How Big Must a Planet Be to Have Plate
Tectonics?......................................349
13.1.6 Exoplanet Temperature Can Be Estimated...................349
13.2 Exoplanet Host Star Properties...................................349
13.2.1 Metal-Rich Stars Are More Likely to Host Gas Giants......349
13.2.2 Did Terrestrial Planets Form 11 Billion Years Ago?.......350
13.2.3 Most Stars with Planets Have Low Lithium Abundance.......350
13.3 Habitable Exoplanets.............................................351
13.3.1 rje Is the Proportion of Stars with Habitable Planets....351
13.3.2 An Earth-Sized Planet in the Habitable Zone Has Been
Discovered...............................................351
13.3.3 How to Define a Habitable Zone...........................352
13.3.3.1 Conservative HZ................................352
13.3.3.2 Optimistic HZ..................................352
13.3.3.3 HZ Location Varies with Stellar Temperature....353
13.3.3.4 Desert Worlds Can Be Very Close to Their
Host Stars......................................353
13.3.3.5 Three-Dimensional Climate Models
Are Needed......................................353
13.3.3.6 The HZ Depends on the Planetary Mass...........354
13.3.3.7 Is a Planet in the HZ?.........................354
13.3.4 r Has Been Derived from Kepler Data....................355
13.3.5 Habitable Planets Around M-Dwarfs?.......................355
13.3.5.1 Habitable Planets Around M-Dwarfs May Be
Tidally Locked..................................356
13.3.5.2 M-Dwarf Radiation Could Be Problematic.........357
13.3.5.3 Red Dwarf Magnetic Fields Are
Problematic................................... 357
13.3.5.4 Planets Around M-Dwarfs Are Probably
Water-Depleted..................................357
13.3.6 Eccentric Orbits Influence Exoplanet Habitability........357
13.3.6.1 Giant Planets Can Clear Out the
Habitable Zone..................................358
13.3.6.2 Can Life Survive on Worlds in
Eccentric Orbits?...............................359
13.3.7 Planets Exist in Binary Systems..........................361
13.3.7.1 S Orbits Are Possible for Close Binaries.......361
13.3.7.2 Habitable Planets Probably Exist in Binary
Systems.........................................361
13.3.7.3 Circumbinary Planets Have Been Identified......363
Contents
xxiii
13.4 The Galactic and Habitability.................................. 366
13.4.1 The Milky Way Is a Spiral Galaxy.........................366
13.4.2 Galactic Chemistry Influences Habitability...............366
13.4.3 The Galaxy Has a Habitable Zone..........................367
13.4.3.1 Low Metallicity Chokes Planet Accretion........367
13.4.3.2 The Galactic Center Is Dangerous...............368
13.4.3.3 The Boundary of the GHZ Has Been Defined.......369
13.4.4 Are There Habitable Planets in Clusters?..................369
13.4.4.1 Globular Clusters Are Probably Barren...........369
13.4.4.2 Open Clusters Likely Harbor Planets.............370
13.4.5 Biosignatures.............................................370
13.4.5.1 Earth Provides Practice in Acquiring
Biosignatures...................................370
13.4.5.2 Atmosphere Spectra Have Been Obtained...........372
13.4.5.3 Water Need Not Mean Habitability................372
13.4.5.4 Some Biosignature Gases Are Produced by
Metabolism......................................373
13.4.5.5 The Red Edge Is a Relatively Unambiguous
Biosignature....................................374
13.4.5.6 Time-Varying Signatures Could indicate
Habitability....................................375
14. Prospecting for Life....................................................377
14.1 Rare Earth versus the Principle of Mediocrity......................377
14.1.1 Is an Early Origin a Guide to the Probability of Life?...377
14.1.1.1 Earth Is Not a Randomly Selected System.........377
14.1.1.2 If Biogenesis Is a Lottery It Is Likely.........378
14.1.1.3 If We Account for Selection Effects
Biogenesis Is Rare..............................378
14.1.2 Life May Be Rare or Common in the Galaxy.................380
14.1.3 Several Hard Steps Could Be Needed for intelligent
Observers to Emerge.......................................381
14.1.3.1 How Many Steps Are Needed?......................381
14.1.4 What Are the Hard Steps?..................................382
14. i 4. 1 Several Hard Step Sequences Have Been
Proposed........................................382
14.1.4.2 Unique Events Are Presumably the Hardest........383
14.1.4.3 Some Events May Have Happened
Only Once.......................................383
14.1.4.4 Is Intelligence with Language Sufficient?.......383
14.2 Is Life Seeded from Space?.........................................383
14.2.1 Survival of Ancient Bacteria Makes Panspermia
Plausible.................................................384
14.2.2 Life May Be Uncommon Despite Panspermia...................384
14.2.3 Radiation Is a Major Hazard...............................385
14.2.3.1 Some Bacteria Have High Radiorésistance.........385
14.2.3.2 Experiments Have Revealed Limits to
Survival in Space...............................386
XXIV
Contents
14.2.4 Can Micro-Organisms Survive Lithopanspermia?..............387
14.2.4.1 Extremophiles Can Survive High Accelerations...387
14.2.4.2 Are We All Martians?............................387
14.3 Metrics for Extraterrestrials.....................................389
14.3.1 Is the Drake Equation More Than a Guess?..................389
14.3.2 Alternatives to the Drake Equation Have Been Developed...391
14.4 SETI and the Fermi Paradox........................................392
14.4.1 Radio SETI................................................393
14.4.2 Optical SETI..............................................393
14.4.3 How Far Away Would Passive Radiation Reveal Our
Presence?.................................................395
14.4.4 Where Is Everybody?.......................................396
14.4.4.1 SETI Has Not Been Long or Far-Reaching
Enough...........................................397
14.4.4.2 Extraterrestrial Civilizations May Be Widely
Separated in Time................................397
14.4.4.3 Extraterrestrial Civilizations Are Widely
Separated in Space...............................397
14.4.4.4 Are There Resource Constraints on Interstellar
Travel?..........................................398
14.4.4.5 Are Extraterrestrial Civilizations Intrinsically
Rare?............................................398
Bibliography................................................................ 399
Index.........................................................................407
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| any_adam_object | 1 |
| author | Longstaff, Alan 1950-2016 |
| author_GND | (DE-588)1123217653 |
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| author_role | aut |
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| author_variant | a l al |
| building | Verbundindex |
| bvnumber | BV042380538 |
| callnumber-first | Q - Science |
| callnumber-label | QH326 |
| callnumber-raw | QH326 |
| callnumber-search | QH326 |
| callnumber-sort | QH 3326 |
| callnumber-subject | QH - Natural History and Biology |
| classification_rvk | US 9800 WH 2800 |
| ctrlnum | (OCoLC)904443385 (DE-599)BVBBV042380538 |
| dewey-full | 576.8/39 576.839 |
| dewey-hundreds | 500 - Natural sciences and mathematics |
| dewey-ones | 576 - Genetics and evolution |
| dewey-raw | 576.8/39 576.839 |
| dewey-search | 576.8/39 576.839 |
| dewey-sort | 3576.8 239 |
| dewey-tens | 570 - Biology |
| discipline | Physik Biologie |
| format | Book |
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| id | DE-604.BV042380538 |
| illustrated | Illustrated |
| indexdate | 2024-07-10T01:20:00Z |
| institution | BVB |
| isbn | 9781439875766 1439875766 |
| language | English |
| oai_aleph_id | oai:aleph.bib-bvb.de:BVB01-027816634 |
| oclc_num | 904443385 |
| open_access_boolean | |
| owner | DE-188 DE-703 |
| owner_facet | DE-188 DE-703 |
| physical | XXXII, 422 S. Ill., graph. Darst. |
| publishDate | 2015 |
| publishDateSearch | 2015 |
| publishDateSort | 2015 |
| publisher | CRC Press |
| record_format | marc |
| series2 | Series in astronomy and astrophysics |
| spelling | Longstaff, Alan 1950-2016 Verfasser (DE-588)1123217653 aut Astrobiology an introduction Alan Longstaff Boca Raton [u.a.] CRC Press 2015 XXXII, 422 S. Ill., graph. Darst. txt rdacontent n rdamedia nc rdacarrier Series in astronomy and astrophysics Exobiology Astrobiologie (DE-588)4112608-7 gnd rswk-swf Astrobiologie (DE-588)4112608-7 s DE-604 Digitalisierung UB Bayreuth - ADAM Catalogue Enrichment application/pdf http://bvbr.bib-bvb.de:8991/F?func=service&doc_library=BVB01&local_base=BVB01&doc_number=027816634&sequence=000003&line_number=0001&func_code=DB_RECORDS&service_type=MEDIA Klappentext Digitalisierung UB Bayreuth - ADAM Catalogue Enrichment application/pdf http://bvbr.bib-bvb.de:8991/F?func=service&doc_library=BVB01&local_base=BVB01&doc_number=027816634&sequence=000004&line_number=0002&func_code=DB_RECORDS&service_type=MEDIA Inhaltsverzeichnis |
| spellingShingle | Longstaff, Alan 1950-2016 Astrobiology an introduction Exobiology Astrobiologie (DE-588)4112608-7 gnd |
| subject_GND | (DE-588)4112608-7 |
| title | Astrobiology an introduction |
| title_auth | Astrobiology an introduction |
| title_exact_search | Astrobiology an introduction |
| title_full | Astrobiology an introduction Alan Longstaff |
| title_fullStr | Astrobiology an introduction Alan Longstaff |
| title_full_unstemmed | Astrobiology an introduction Alan Longstaff |
| title_short | Astrobiology |
| title_sort | astrobiology an introduction |
| title_sub | an introduction |
| topic | Exobiology Astrobiologie (DE-588)4112608-7 gnd |
| topic_facet | Exobiology Astrobiologie |
| url | http://bvbr.bib-bvb.de:8991/F?func=service&doc_library=BVB01&local_base=BVB01&doc_number=027816634&sequence=000003&line_number=0001&func_code=DB_RECORDS&service_type=MEDIA http://bvbr.bib-bvb.de:8991/F?func=service&doc_library=BVB01&local_base=BVB01&doc_number=027816634&sequence=000004&line_number=0002&func_code=DB_RECORDS&service_type=MEDIA |
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