Acknowledgements xv About the CompanionWebsite xvii
1 Astrobiology and Life 1
1.1 About this Textbook 1
1.2 Astrobiology and Life 4
1.3 What is Astrobiology? 4
1.4 History of Astrobiology 6
1.5 What is Life? 9
1.6 Conclusions 12
Further Reading 12
2 Matter, the Stuff of Life 13
2.1 Matter and Life 13
2.2 We are Made of `Ordinary’ Matter 13
2.3 Matter: Its Nucleus 14
2.3.1 Isotopes 14
2.4 Electrons, Atoms and Ions 15
2.5 Types of Bonding in Matter 15
2.6 Ionic Bonding 15
2.6.1 Ionic Bonds and Life 16
2.7 Covalent Bonding 17
2.7.1 Covalent Bonds and Life 17
2.8 Metallic Bonding 19
2.9 van der Waals’ Interactions 19
2.9.1 Dipole–dipole (Keesom) Forces 19
2.9.2 Dipole–induced Dipole (Debye; Pronounced deh-beye) Forces
19
2.9.3 Dispersion Forces 20
2.9.4 van der Waals’ Interactions and Life 20
2.10 Hydrogen Bonding 20
2.10.1 Hydrogen Bonds and Life 21
2.11 The Equation of State Describes the Relationship between
Different Types of Matter 21
2.12 Phase Diagrams 22
2.12.1 Matter and Mars 23
2.12.2 Phase Diagrams and Life 24
2.13 Other States of Matter 25
2.13.1 Plasma 25
2.13.2 Degenerate Matter 25
2.14 The Interaction between Matter and Light 27
2.14.1 The Special Case of the Hydrogen Atom 29
2.14.2 Uses to Astrobiology 29
2.15 Conclusions 30
Further Reading 30
3 Life’s Structure: Building the Molecules 33
3.1 Building Life 33
3.2 The Essential Elements: CHNOPS 33
3.3 Carbon is Versatile 34
3.4 The Chains of Life 35
3.5 Proteins 35
3.6 Chirality 37
3.7 Carbohydrates (Sugars) 38
3.8 Lipids 39
3.9 The Nucleic Acids 39
3.9.1 Ribonucleic Acid 40
3.10 The Solvent of Life 43
3.10.1 Water as the Best Solvent 43
3.11 Alternative Chemistries 44
3.11.1 Alternative Core Elements 44
3.11.2 Alternative Solvents 47
3.12 The Structure of Life and Habitability 48
3.13 Conclusion 49
Further Reading 49
4 Life’s Structure: Building Cells from Molecules 51
4.1 From Molecules to Cells 51
4.2 Types of Cells 51
4.3 Shapes of Cells 53
4.4 The Structure of Cells 53
4.5 Membranes 55
4.5.1 Gram-negative and Positive Prokaryotic Membranes 56
4.5.2 Archeal Membranes 58
4.6 The Information Storage System of Life 58
4.6.1 Transcription – DNA to RNA 59
4.6.2 Translation – RNA to Protein 60
4.6.3 A Remarkable Code 62
4.6.4 DNA Replication 62
4.6.5 Plasmids 64
4.6.6 eDNA 65
4.7 Cell Reproduction 65
4.8 The Growth of Life 67
4.9 Moving and Communicating 68
4.9.1 Movement in Prokaryotes 68
4.9.2 Communication in Prokaryotes 68
4.10 Eukaryotic Cells 70
4.10.1 Endosymbiosis 72
4.11 Viruses 72
4.12 Prions 74
4.13 Conclusions 74
Further Reading 74
5 EnergyforLife 77
5.1 Energy and Astrobiology 77
5.2 Life and Energy 78
5.3 The Central Role of Adenosine Triphosphate 78
5.4 Chemiosmosis and Energy Acquisition 80
5.5 What Types of Electron Donors and Acceptors can be Used? 83
5.6 Aerobic Respiration 83
5.7 Anaerobic Respiration 86
5.8 Fermentation 88
5.9 Chemoautotrophs 88
5.9.1 Methanogens and Methanotrophs 90
5.9.2 Sulfur Cycling 91
5.9.3 Iron Oxidisers 91
5.9.4 Nitrogen Cycling and the Chemoautotrophs 91
5.10 Energy from Light: Oxygenic Photosynthesis 92
5.11 Anoxygenic Photosynthesis 94
5.12 Global Biogeochemical Cycles 97
5.13 Microbial Mats – Energy-driven Zonation in Life 99
5.14 The Thermodynamics of Energy and Life 100
5.14.1 Gibbs Free Energy: The Energy in Reactants and Products
100
5.14.2 Gibbs Free Energy: The Concentration of Compounds 100
5.14.3 Gibbs Free Energy: Using Redox Reactions 100
5.15 Life in Extremes 103
5.16 Conclusions 103
Further Reading 103
6 TheTreeofLife 105
6.1 A Vast Diversity of Life 105
6.2 The Tree of Life 106
6.3 Some Definitions 106
6.4 Classifying Organisms 106
6.5 Homology and Analogy 109
6.6 Building a Phylogenetic Tree 110
6.7 Some Definitions and Phylogenetic Trees 112
6.8 Types of Phylogenetic Trees 113
6.9 Using Phylogenetic Trees to Test Hypotheses 113
6.10 Complications in Building the Universal Tree of Life 115
6.10.1 Endosymbiosis 116
6.10.2 Horizontal Gene Transfer 117
6.11 The Last Universal Common Ancestor 119
6.12 Molecular Clocks 120
6.13 Alien Life 121
6.14 Conclusions 121
Further Reading 121
7 The Limits of the Biospace 123
7.1 The Biospace 123
7.2 The Importance of the Biospace for Astrobiology 123
7.3 The Edges of the Biospace are Dominated by Microbes 124
7.4 Life at High Temperatures 126
7.4.1 Uses for Thermostable Molecules 127
7.5 Life at Low Temperatures 127
7.6 Salt-loving Organisms 129
7.6.1 Salt-in Strategy 130
7.6.2 Salt-out Strategy 130
7.6.3 Low Water Activity 130
7.7 pH Extremes 130
7.8 Life Under High Pressure 132
7.9 Tolerance to High Radiation 132
7.10 Life in Toxic Brews 134
7.11 Life on the Rocks 134
7.12 Polyextremophiles – dealing with Multiple Extremes 136
7.13 Life Underground 137
7.14 Dormancy in Extreme Conditions 138
7.15 Eukaryotic Extremophiles 139
7.16 Are there Other Biospaces? 140
7.17 The Limits of Life: Habitability Revisited 140
7.18 Conclusions 140
Further Reading 141
8 The Formation of the Elements of Life 143
8.1 In the Beginning 143
8.2 Low Mass Stars 147
8.3 High Mass Stars 149
8.4 The Elements of Life 150
8.5 The Hertzsprung–Russell Diagram 152
8.6 The Sun is a Blackbody 156
8.7 The Formation of Planets 157
8.8 Types of Objects in our Solar System 159
8.9 Laws Governing the Motion of Planetary Bodies 160
8.10 Meteorites 163
8.11 Conclusions 165
Further Reading 165
9 Astrochemistry – Carbon in Space 167
9.1 Astrochemistry: The Molecules of Life? 167
9.2 Observing Organics 167
9.3 In the Beginning 168
9.4 Different Environments 169
9.4.1 Diffuse Interstellar Clouds 169
9.4.2 Molecular Clouds 169
9.4.3 Protoplanetary Disc 170
9.4.4 Carbon-rich Stars 171
9.4.5 Shock Waves from Supernova Explosions and Other Astrophysical
Violence 172
9.5 How are Compounds Formed? 172
9.6 Interstellar Grains 174
9.7 Forming Carbon Compounds 175
9.8 Polycyclic Aromatic Hydrocarbons 176
9.9 Even More Carbon Diversity 176
9.9.1 Prebiotic Compounds 177
9.10 Comets 178
9.11 Chirality 179
9.12 Laboratory Experiments 179
9.13 Observing these Molecules 180
9.14 Conclusions 181
Further Reading 182
10 The Early Earth (The First Billion Years) 183
10.1 The First Billion Years of the Earth 183
10.2 The Earth Forms and Differentiates 183
10.3 The Formation of the Moon 184
10.4 The Early Oceans 186
10.5 The Early Crust 187
10.6 The Early Atmosphere 188
10.7 The Temperature of the Early Earth 189
10.8 The Late Heavy Bombardment 189
10.9 Implications of the Early Environment for Life 192
10.10 Conclusion 194
Further Reading 194
11 The Origin of Life 197
11.1 Early Thoughts on the Origin of Life: Spontaneous Generation
197
11.2 Some Possible Ideas for the Origin of Life 200
11.3 The Synthesis of Organic Compounds on the Earth 200
11.3.1 Possible Reaction Pathways 202
11.4 Delivery from the Extraterrestrial Environment 204
11.5 The RNA World 206
11.6 Early Cells 208
11.7 Where did it Happen? 210
11.7.1 Deep Sea Hydrothermal Vents 210
11.7.2 Land-based Volcanic Pools 211
11.7.3 Impact Craters 211
11.7.4 Beaches 212
11.7.5 Bubbles 213
11.7.6 The Deep Sub-Surface 213
11.7.7 Mineral Surfaces 213
11.8 A Cold Origin of Life? 214
11.9 The Whole Earth as a Reactor? 214
11.10 Conclusions 214
Further Reading 214
12 Early Life on Earth 217
12.1 Early Life on the Earth 217
12.2 Early Life – Metabolisms and Possibilities 217
12.3 Isotopic Fractionation 220
12.3.1 Carbon Isotopes 221
12.4 Measuring the Isotope Fraction: The Delta Notation 221
12.5 Sulfur Isotope Fractionation 223
12.6 Using Ancient Isotopes to Look for Life 223
12.7 Morphological Evidence for Life 225
12.7.1 How are Microorganisms Fossilised? 225
12.7.2 Evidence for Fossil Microbial Life 225
12.7.3 Stromatolites 229
12.8 Biomarkers 230
12.9 The Search for Extraterrestrial Life 230
12.10 Conclusions 231
Further Reading 231
13 The History of the Earth 233
13.1 The Geological History of the Earth 233
13.2 Minerals and Glasses 233
13.3 Types of Rocks 235
13.3.1 Igneous Rocks 235
13.3.2 Sedimentary Rocks 235
13.3.3 Metamorphic Rocks 236
13.4 The Rock Cycle 237
13.5 The Composition of the Earth 239
13.6 The Earth’s Crust and Upper Mantle 239
13.7 Plate Tectonics 240
13.8 Dating Rocks 244
13.9 Age-dating Rocks 246
13.9.1 Absolute Dating of Rocks 246
13.9.2 Relative Dating 250
13.9.3 Unconformities 251
13.10 Geological Time Scales 252
13.11 The Major Classifications of Geological Time 252
13.12 Some Geological Times and Biological Changes 254
13.12.1 The Precambrian 254
13.12.2 The Phanerozoic: The Rise of Animals and Complexity 254
13.13 Conclusion 259
Further Reading 260
14 The Rise of Oxygen 261
14.1 Dramatic Changes on the Earth 261
14.2 Measuring Oxygen Through Time 262
14.2.1 Minerals that Form at Low Oxygen Concentrations 262
14.2.2 Changes in the Oxidation State of Elements 263
14.2.3 Banded Iron Formations and their Isotopes 264
14.2.4 Sulfur Isotope Fractionation 264
14.3 Summarising the Evidence for the Great Oxidation Event 265
14.4 The Source of Oxygen 266
14.5 Sinks for Oxygen 266
14.6 Why did Oxygen Rise? 267
14.7 Snowball Earth Episodes 268
14.8 Other Biological Consequences of the Rise of Oxygen 270
14.9 Oxygen and the Rise of Animals 271
14.10 Periods of High Oxygen 272
14.11 Conclusions 273
Further Reading 273
15 Mass Extinctions 275
15.1 Extinction 275
15.2 What is Extinction? 275
15.3 Five Major Mass Extinctions 277
15.4 Other Extinctions in Earth History 278
15.5 Causes of Mass Extinction 278
15.6 The End-Cretaceous Extinction 279
15.7 The Other Four Big Extinctions of the Phanerozoic 284
15.7.1 End-Ordovician Mass Extinction 284
15.7.2 Late Devonian Mass Extinction 285
15.7.3 The Largest of all Mass Extinctions: The End-Permian
Extinction 285
15.7.4 End-Triassic Mass Extinction 287
15.8 Impacts and Extinction 287
15.9 Some Questions About Extinctions and Life 287
15.10 The Sixth Mass Extinction? 289
15.11 Conclusions 290
Further Reading 290
16 The Habitability of Planets 291
16.1 What is Habitability? 291
16.2 The Habitable Zone 292
16.2.1 Star Types 293
16.2.2 Continuously Habitable Zone 294
16.2.3 The Galactic Habitable Zone 294
16.2.4 The Right Galaxy? 295
16.3 Maintaining Temperature Conditions on a Planet Suitable for
Water and Life 295
16.3.1 Effective Temperature and the Greenhouse Effect 295
16.3.2 The Carbonate–Silicate Cycle 297
16.4 Plate Tectonics 299
16.5 Do We Need a Moon? 300
16.6 Surface Liquid Water, Habitability and Intelligence 301
16.7 Uninhabited Habitats: Habitats Need Not Always Contain Life
301
16.8 Worlds More Habitable than the Earth? 302
16.9 The Anthropic Principle 303
16.10 The Fate of the Earth 303
16.11 Conclusions 304
Further Reading 304
17 The Astrobiology of Mars 307
17.1 Mars and Astrobiology 307
17.2 Martian History: A Very Brief Summary 308
17.3 The Deterioration of Mars 309
17.4 Missions to Mars 311
17.5 Mars and Life 314
17.5.1 Liquid Water and Mars 314
17.5.2 Basic Elements for Life on Mars 320
17.5.3 Trace Elements for Life on Mars 321
17.5.4 Energy and Redox Couples for Life on Mars 321
17.5.5 Physical Limits to Life: Radiation 324
17.5.6 Physical Limits to Life: pH 324
17.5.7 Physical Limits to Life: Salts 325
17.5.8 Habitat Space for Microbes on Mars 325
17.6 Trajectories of Martian Habitability 325
17.6.1 Trajectories for an Uninhabited Mars 326
17.6.2 Trajectories for an Inhabited Mars 328
17.7 The Viking Programme and the Search for Life 329
17.7.1 GCMS Analysis 329
17.7.2 Gas Exchange Experiment 329
17.7.3 Labelled Release Experiment 330
17.7.4 Pyrolytic Release Experiment 330
17.7.5 Viking: A Lesson in Science 331
17.8 Martian Meteorites 331
17.9 Mars Analogue Environments 333
17.10 Panspermia – Transfer of Life Between Planets? 333
17.10.1 Ejection from a Planet 334
17.10.2 Interplanetary Transfer Phase 335
17.10.3 Arriving at the Destination Planet 336
17.11 Conclusions 338
Further Reading 338
18 The Moons of Giant Planets 341
18.1 The Astrobiology of Moons 341
18.2 The Moons of Jupiter: Europa 342
18.2.1 A Sub-Surface Ocean? 344
18.3 The Moons of Jupiter: Ganymede and Callisto 347
18.4 The Moons of Jupiter: Io 348
18.5 The Moons of Saturn: Enceladus 349
18.5.1 The Plumes of Enceladus 349
18.6 The Moons of Saturn: Titan 352
18.7 Other Icy Worlds 359
18.7.1 Triton 359
18.7.2 Ceres 359
18.7.3 Pluto 360
18.8 Planetary Protection 360
18.9 Conclusions 362
Further Reading 362
19 Exoplanets: The Search for Other Habitable Worlds 363
19.1 Exoplanets and Life 363
19.2 Detecting Exoplanets 364
19.3 Transit Method for Detecting Exoplanets 364
19.4 Doppler Shift/Radial Velocity Method of Detecting Exoplanets
366
19.5 Astrometry 368
19.6 Variations in Other Attributes of Stars 368
19.7 Orbital Brightness Changes 368
19.8 Gravitational Lensing 368
19.9 Direct Detection 369
19.10 Using Direct Detection to Study Protoplanetary Discs 369
19.11 Exoplanet Properties 371
19.11.1 General Properties 371
19.11.2 Hot Jupiters and Neptunes 371
19.11.3 Super-Earths and Ocean Worlds 371
19.11.4 Rocky Planets in the Habitable Zone 374
19.11.5 Planets in Binary and Multiple Star Systems 374
19.11.6 Strange Worlds 375
19.12 Detecting Life 376
19.12.1 Biosignature Gases 376
19.12.2 Surface Biosignatures 380
19.12.3 How Likely are These Signatures? 381
19.13 Conclusions 382
Further Reading 382
20 The Search for Extraterrestrial Intelligence 385
20.1 The Search for Extraterrestrial Intelligence 385
20.2 The Drake Equation 386
20.3 Methods in the Search for Extraterrestrial Intelligence
387
20.4 Communication with Extraterrestrial Intelligence 389
20.5 The Fermi Paradox 391
20.5.1 Civilisations are too Far Apart in Space 393
20.5.2 No Other, or Very Few, Civilisations have Arisen 393
20.5.3 Intelligent Life Destroys Itself 394
20.5.4 Life is Periodically Destroyed by Natural Events 394
20.5.5 It is the Nature of Intelligent Life to Destroy Other
Civilisations 394
20.5.6 They Exist, But We See No Evidence of Them 394
20.5.7 They are in the Local Area, But Observing us Rather Than
Attempting to Make Contact 395
20.5.8 They are too Busy Online 395
20.5.9 They are Here 395
20.5.10 The Evidence is Being Suppressed 395
20.6 Classifying Civilisations 396
20.7 Policy Implications 397
20.8 Conclusions 398
Further Reading 398
21 Our Civilisation 399
21.1 Astrobiology and Human Civilisation 399
21.2 The Emergence of Human Society 399
21.3 Threats to a Civilisation 402
21.4 Climate Change and the Challenge to Seven Billion Apes 404
21.5 The Human Future Beyond the Earth 407
21.5.1 The Rocket Equation 407
21.6 Settling the Solar System 408
21.7 Avoiding Extinction or Collapse: A Multiplanet Species 411
21.8 Environmentalism and Space Exploration as a Single Goal?
413
21.9 Sociology: The Overview Effect 414
21.10 Will We Become Interstellar? 414
21.11 Conclusions 415
Further Reading 415
Appendix 417
A.1 The Astrobiological Periodic Table 417
A.2 Units and Scales 417
A.2.1 Standard International Base Units 417
A.2.2 Basic Physical Constants 418
A.3 Temperature Scale Conversion 418
A.4 Composition of the Sun 419
A.5 Some of the Major Star Types and Temperatures and Colour
419
A.6 Three- and One-letter Designations of Amino Acids 419
A.7 Codon Table for the Genetic Code (also shown in Chapter 4;
Figure 4.12) 420
A.8 Planetary Data 421
A.9 Geological Time Scale 421
Glossary 423
Index 443
Charles Cockell is Professor of Astrobiology at the University of Edinburgh. His research interests are focused on the study of life in extreme environments and understanding the habitability of planets. After a doctorate at the University of Oxford he worked at the NASA Ames Research Centre, the British Antarctic Survey and The Open University. He has published widely in astrobiology and carried out fieldwork in locations from the Arctic to the Antarctic.
"Cockell’s Astrobiology is a high-level but entirely approachable
textbook that will likely be used in many universities.
Astrobiology Journal (vol 15, no.5, 2016)
"A hugely useful resource for new students of astrobiology,
regardless of your background or `home’ discipline."
Lewis Dartnell, The Astrobiology Society of Britain
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