Earliest Life on Earth: Habitats, Environments and Methods of Detection (eBook)

Preface 5
Contents 9
Contributors 11
Dedication to John F. Lindsay 15
Introduction 17
References 24
Earliest Seafloor Hydrothermal Systems on Earth: Comparison with Modern Analogues 29
1 Introduction 30
2 Sulfur Isotopes in Seafloor Hydrothermal Systems and Sediments 31
3 Geologic Setting of Dresser Formation and Sulphur Springs Deposit 34
4 Sampling and Analytical Methods 36
5 Geochronology 40
6 Stable Isotopes 45
6.1 Dresser Formation 46
6.2 Sulphur Springs 51
7 Summary and Conclusions 55
References 56
Archaean Hydrothermal Systems in the Barberton Greenstone Belt and Their Significance as a Habitat for Early Life 64
1 Introduction 64
2 Geological Setting 65
2.1 Onverwacht Group 65
2.2 Fig Tree Group 66
2.3 Moodies Group 68
3 Hydrothermal Systems in the Onverwacht Group 68
3.1 Silica Alteration Zones 68
3.2 Bedded Cherts 71
3.3 Chert Veins 73
3.4 Ironstone Pods: Archaean Hydrothermal Systems or Products of Recent Weathering 74
3.5 Heat Source for Onverwacht Hydrothermal Activity 76
3.6 Buck Reef Chert: Deposition During Hydrothermal or Normal Marine Conditions? 77
4 Hydrothermal Systems of the Fig Tree Group 81
4.1 Baryte 81
4.2 Hydrothermally Altered Shales and Sandstones 83
4.3 Bien Venue Massive Sulphide Deposit 84
4.4 Heat Source for Fig Tree Hydrothermal Activity 85
5 Implications of Hydrothermal Activity for Early Life in the Barberton Greenstone Belt 86
References 87
Birth of Biomolecules from the Warm Wet Sheets of Clays Near Spreading Centers 92
1 Introduction 93
2 The Primordial Womb Hypothesis 94
3 Background 97
3.1 Organic Geochemistry 97
3.2 Clay Minerals 98
3.3 Natural Clays in Hydrothermal Systems 102
4 Experimental Design for Evaluating the Role of Clay in Biosynthesis Reactions 102
4.1 Experimental Methods 104
4.2 Analytical Methods 104
4.2.1 Organic 104
4.2.2 Mineral 105
5 Results 105
5.1 Summary of Experimental Results 107
6 Discussion 107
6.1 Thermodynamic Analysis of the Hydrothermal Organic Synthesis Experiment 108
6.2 Reaction Pathways of the Hydrothermal Organic Synthesis Experiment 109
6.2.1 Early-Stage Reactions: Hydrogen Production 109
6.2.2 Late-Stage Reactions: Clay–Surface Interactions 113
6.2.3 Hydrogen Consumption in Montmorillonite-Containing Experiments 115
6.2.4 Oxidation State 117
7 Summary 117
references 119
Towards a Null Hypothesis for Stromatolites 127
1 Peculiar Contortions 127
2 Implications 133
References 136
Trace Element Geochemistry as a Tool for Interpreting Microbialites 138
1 Introduction 139
1.1 How Do Microbialites Form? 141
1.2 Biosignatures in Microbialites 146
2 Trace Element Geochemistry and Microbialites 148
2.1 The Use of Trace Elements to Help Reconstruct Environments of Deposition 151
2.2 Effect of Microenvironments on Trace Element Inventories 155
2.3 Bioactive Metal Accumulation 158
3 Diagenetic Disruption of Trace Metal Signatures 162
4 Outlook 164
5 Summary 169
References 170
A Modern Perspective on Ancient Life: Microbial Mats in Sandy Marine Settings from the Archean Era to Today 182
1 Introduction 182
2 Microbially Induced Sedimentary Structures – MISS 184
3 Modern MISS and Their Formation 186
4 Classification of MISS 187
5 How to Interprete Archean MISS by Using Modern Analogues of the Structures 189
6 Conclusive Remarks and the Question Which Microbiota Formed Microbial Mats in the Archean Era 190
References 191
Early Life Record from Nitrogen Isotopes 194
1 Introduction 195
2 Nitrogen in Rocks 196
3 Nitrogen Isotopes in Modern Marine Sediments: The Cycle 197
4 The Preservation of the Isotopic Signature of N in the Rock Record: The Role of Metamorphism and Alteration 199
5 The Significance of 15N-Depleted Nitrogen in Early Archean Organic Matter 202
6 Isotopic Shifts Recorded by N, C and Fe at Late Archean: A Reaction to the Progressive Oxygenation of the Earth 206
7 Enhanced Denitrification or N Imbalanced Fluxes in the Ocean as a Response to the Oxygenation of the Earth 208
8 Conclusions 210
References 211
Integration of Observational and Analytical Methodologies to Characterize Organic Matter in Early Archaean Rocks 218
1 Introduction 219
2 Geological Setting of the Warrawoona Group 221
2.1 Dresser Formation 222
2.2 Apex Basalt 223
3 Materials and Methodology 224
3.1 Organic Petrology 224
3.2 Electron Microscopy 225
3.3 C-Isotope Analysis 225
3.4 Total Organic Carbon (TOC) and Elemental Analysis 226
4 Results and Discussion 226
4.1 Dresser Formation Carbonaceous Matter 227
4.2 Apex Basalt Carbonaceous Matter 233
4.3 Elemental and Carbon Isotope Compositions of CM 237
5 Summary and Conclusions 240
References 242
Bugs or Gunk? Nanoscale Methods for Assessing the Biogenicity of Ancient Microfossils and Organic Matter 247
1 Introduction 248
1.1 Structure and Bonding of Kerogen 249
1.2 Abiotic Fischer-Tropsch-Type Carbonaceous Matter 251
1.3 Putative Archean Microfossils and Stromatolites from Western Australia 253
2 Methods 254
2.1 Samples and Standards 254
2.2 Sulfur Embedding and Ultramicrotomy 255
2.3 FTT Sample Preparation 258
2.4 Scanning Transmission X-ray Microscopy (STXM) 259
2.5 X-ray Absorption Near-Edge Structure Spectroscopy (XANES) 262
2.6 Tranmission Electron Microscopy (TEM) 263
2.7 Electron Energy-Loss Near-Edge Structure Spectroscopy (ELNES) 266
3 Results 267
3.1 Apex Carbonaceous Matter 267
3.2 Strelley Pool Carbonaceous Matter 272
3.3 Gunflint Kerogen 274
3.4 Fischer-Tropsch-Type Carbonaceous Matter 275
4 Discussion 280
4.1 Beam Damage of Carbonaceous Matter by STXM and TEM 280
4.2 Spectral Differences Between XANES and ELNES 283
4.3 Structure and Bonding of Precambrian Carbonaceous Matter 284
4.4 Comparison with FTT Carbonaceous Matter 284
4.5 Controversy Surrounding the Apex Microfossils 285
4.6 Controversy Surrounding the Strelley Pool Stromatolites 288
4.7 Archean Hydrothermal Microbial Communities 289
5 Summary 290
References 290
What Can Carbon Isotopes Tell Us About Sources of Reduced Carbon in Rocks from the Early Earth? 298
1 Introduction 298
2 Sources of Reduced Carbon and Their Isotopic Compositions 300
2.1 Biological Sources 301
2.2 Abiotic Sources 303
2.2.1 Exogenous Inputs 303
2.2.2 Endogenous Inputs 305
3 Carbon Isotopes and the Early Geologic Record 308
3.1 Isotopic Composition of Organic Matter Through Time 308
3.2 Reduced Carbon in Rocks from Southwest Greenland 310
3.3 Carbon Isotopes and Putative Microfossils in the Warrawoona Group 312
4 Concluding Remarks 314
References 315
Index 319