Life in the Universe: Expectations and Constraints

Life in the Universe: Expectations and Constraints

by Dirk Schulze-Makuch, Louis Neal Irwin
     
 

ISBN-10: 3540307087

ISBN-13: 9783540307082

Pub. Date: 02/28/2006

Publisher: Springer Berlin Heidelberg

Examines each of these parameters in crucial depth and makes the argument that life forms we would recognize may be more common in our solar system than many assume.

Considers exotic forms of life that would not have to rely on carbon as the basic chemical element, solar energy as the main energy source, or water as the primary solvent and the question of

Overview

Examines each of these parameters in crucial depth and makes the argument that life forms we would recognize may be more common in our solar system than many assume.

Considers exotic forms of life that would not have to rely on carbon as the basic chemical element, solar energy as the main energy source, or water as the primary solvent and the question of detecting bio- and geosignatures of such life forms, ranging from earth environments to deep space.

Seeks an operational definition of life and investigate the realm of possibilities that nature offers to realize this very special state of matter.

Avoids scientific jargon wherever possible to make this intrinsically interdisciplinary subject understandable to a broad range of readers.

Product Details

ISBN-13:
9783540307082
Publisher:
Springer Berlin Heidelberg
Publication date:
02/28/2006
Series:
Advances in Astrobiology and Biogeophysics Series
Edition description:
1st ed 2004. 2nd printing
Pages:
172
Product dimensions:
6.32(w) x 9.26(h) x 0.47(d)

Table of Contents

1 Introduction 1

2 Definition of Life 7

2.1 Problems with Common Assumptions about the Nature of Life 7

2.2 Historical Views on the Definition of Life 12

2.3 Modern Definitions of Life 13

2.4 Thermodynamic Criteria 14

2.5 Bioinformatic Criteria 15

2.6 Evolutionary Criteria 16

2.7 Life as a Global Entity 16

2.8 Life as a Collection of Attributes 17

2.9 A Utilitarian and Generic View 17

2.9.1 Self-organizing and Bounded Environments in Thermodynamic Disequilibrium 18

2.9.2 Transformation of Energy to Maintain a Low Entropy State and Perform Work 20

2.9.3 Information Encoding and Transmission 21

2.10 Implications for the Remote Detection of Life 22

2.11 Chapter Summary 24

3 Origin of Life 25

3.1 Scenarios for the Origin of Life 25

3.1.1 A Lukewarm Marine Origin of Life 27

3.1.2 A Benthic Thermophilic Origin of Life 28

3.1.3 An Ice Water Origin of Life 28

3.1.4 A Comprehensive Scenario for the Origin of Life 29

3.2 Inferences for the First Cellular Membranes 32

3.3 Inferences with Regard to the First Metabolism 33

3.4 Inferences for the First Replication Mechanism 35

3.5 Other Inferences 37

3.5.1 Size 37

3.5.2 Environmental Conditions 37

3.5.3 Medium 38

3.5.4 Minerals and Substrates 39

3.5.5 Implications for the Possibility of Life on Other Worlds 40

3.6 Chapter Summary 41

4 Lessons from the History of Life on Earth 43

4.1 A Brief History of Life on Earth 43

4.2 Lessons from the History of Life on Earth 45

4.2.1 Life Arises Relatively Quickly under Conducive Conditions 45

4.2.2 Life Tends to Stay Small and Simple 46

4.2.3 Most Organisms Remain Relatively Unchanged over their Evolutionary Life Spans 47

4.2.4 Evolutionis Accelerated by Environmental Changes 49

4.2.5 Complexity Inevitably Increases but as the Exception rather than the Rule 50

4.2.6 Biodiversity is Promoted by Heterogeneous Environments 51

4.2.7 Individuals are Fragile, but Life is Hardy 52

4.3 Adaptations to Extreme Environments 52

4.3.1 Temperature Extremes 54

4.3.2 Extreme pH-Conditions 56

4.3.3 Low Availability of Water 57

4.3.4 Low Oxygen Availability 59

4.3.5 Pressure 60

4.3.6 Radiation 61

4.3.7 Low Nutrient Availability and Chemical Extremes 62

4.4 Questions Unanswered by the History of Life on Earth 63

4.5 Chapter Summary 64

5 Energy Sources and Life 65

5.1 Life As We Know It 65

5.1.1 Oxidation-Reduction Chemistry as an Energy Source for Life 66

5.1.2 Light as an Energy Source for Life 68

5.2 Life As We Don't Know It 68

5.2.1 Electromagnetic Waves (other than Visible Light) 69

5.2.2 Thermal Energy 70

5.2.3 Kinetic Energy 73

5.2.4 Osmotic or Ionic Gradients 74

5.2.5 Magnetic Fields 77

5.2.6 Gravitational Forces 81

5.2.7 Tectonic Stress 82

5.2.8 Pressure Gradients 82

5.2.9 Spin Configurations 83

5.2.10 Radioactivity 84

5.3 The Question of Entropy, Uniformity, and Origin 85

5.4 Survey of Energy Sources in our Solar System 86

5.5 Chapter Summary 88

6 Building Blocks of Life 89

6.1 The Uniqueness of Carbon 89

6.2 An Alien Carbon Biochemistry? 93

6.3 Alternatives to Carbon as the Universal Building Block of Life 94

6.4 The Possibility of Silicon-Based Life 95

6.4.1 Physical Properties of Silicon 95

6.4.2 Role of Silicon for Life on Earth 97

6.4.3 Polymeric Chemistry of Silicon 100

6.4.4 Environmental Conditions for the Possibility of Silicon-Based Life 102

6.5 Other Alternatives as Building Blocks of Life 106

6.6 Chapter Summary 108

7 Life and the Need for a Solvent 109

7.1 Water as the Universal Solvent for Life on Earth 111

7.2 Polar Inorganic Solvents as Alternatives to Water 116

7.2.1 Ammonia 117

7.2.2 Hydrocyanic Acid 120

7.2.3 Hydrofluoric Acid 121

7.2.4 Hydrogen Sulfide, Sulfur Dioxide and Sulfuric Acid 122

7.2.5 Hydrogen Peroxide 123

7.2.6 Hydrazine 124

7.2.7 Supercritical Fluids: Carbon Dioxide 124

7.3 Organic and Non-Polar Solvents 125

7.3.1 Organic Non-Polar Compounds 126

7.3.2 Organic Polar Compounds 127

7.3.3 Inorganic Non-Polar Compounds 128

7.4 Quantitative Assessment of Solvent Candidates 128

7.5 Some Additional Thoughts 131

7.6 Chapter Summary 132

8 Habitats of Life 133

8.1 Life on the Surface 133

8.2 Life Beneath the Surface 134

8.3 Life in the Atmosphere 137

8.4 Life in the Space Environment 141

8.5 Cosmic Biogeography 143

8.6 Chapter Summary 147

9 Ideas of Exotic Forms of Life 149

9.1 Life Based on Spin Configurations 149

9.2 Fred Hoyle's Black Cloud and Similar Ideas 151

9.3 Life on a Neutron Star 151

9.4 Life on a Brown Dwarf 152

9.5 Life on a Rogue Planet 153

9.6 Some Other Ideas on Forms of Exotic Life 153

9.7 Chapter Summary 154

10 The Future and Fate of Living Systems 155

10.1 Evolutionary Alternatives 155

10.1.1 Plateau 156

10.1.2 Collapse 157

10.1.3 Transition 158

10.2 Evolution of Intelligence 159

10.3 The Rise of Technological Competence and its Fate 160

10.4 Application to the Possibility of Life on other Worlds 162

10.5 Chapter Summary 163

11 Signatures of Life 165

11.1 Searching for Signatures of Life 165

11.1.1 Atmospheric Composition of a Planetary Body 166

11.1.2 Geological Evidence 167

11.1.3 Fossil Evidence 168

11.1.4 Macromolecules and Chirality 169

11.1.5 Presence of Metabolic By-Products and End-Products 169

11.1.6 Production of Biogenic Heat 170

11.1.7 Signatures of More Advanced Life 170

11.2 Geoindicators of Life 171

11.2.1 Presence of an Atmosphere or Ice Shield 171

11.2.2 Internal Differentiation 172

11.2.3 Polymeric Chemistry 173

11.2.4 Energy Source 173

11.2.5 Liquid Medium 175

11.3 Geoindicators for Life in our Solar System 176

11.4 Extrasolar Planetary Detection 180

11.5 Chapter Summary 182

12 Life Detection - Past and Present 183

12.1 The Viking Mission 183

12.1.1 The Viking Landers 183

12.1.2 Mission Preparation 185

12.1.3 Mission Results 186

12.1.4 Interpretation of Mission Results 188

12.2 Martian Meteorites and Evidence for Ancient Life 191

12.2.1 The Claim of Fossilized Life in Martian Meteorite ALH84001 192

12.2.2 A Cold Reception by the Scientific Community 194

12.2.3 Signs of Ancient Life in another Martian Meteorite? 198

12.2.4 Conclusions Concerning Biomarkers in Martian Meteorites 199

12.3 Current Life Detection Instrumentation 199

12.4 Planetary Protection Considerations 201

12.5 Chapter Summary 201

13 Optimizing Space Exploration 203

13.1 Mars 204

13.1.1 Robotic Missions to Mars 204

13.1.2 Human Missions to Mars 205

13.1.3 A Vision for Mars Exploration 207

13.2 The Moon 208

13.3 Venus 209

13.4 Other Exploration Targets 209

13.5 Chapter Summary 211

References 213

Index 243

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