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

Preface

Contents

Contributors

Dedication to John F. Lindsay

Introduction

References

Earliest Seafloor Hydrothermal Systems on Earth: Comparison with Modern Analogues

1 Introduction

2 Sulfur Isotopes in Seafloor Hydrothermal Systems and Sediments

3 Geologic Setting of Dresser Formation and Sulphur Springs Deposit

4 Sampling and Analytical Methods

5 Geochronology

6 Stable Isotopes

6.1 Dresser Formation

6.2 Sulphur Springs

7 Summary and Conclusions

References

Archaean Hydrothermal Systems in the Barberton Greenstone Belt and Their Significance as a Habitat for Early Life

1 Introduction

2 Geological Setting

2.1 Onverwacht Group

2.2 Fig Tree Group

2.3 Moodies Group

3 Hydrothermal Systems in the Onverwacht Group

3.1 Silica Alteration Zones

3.2 Bedded Cherts

3.3 Chert Veins

3.4 Ironstone Pods: Archaean Hydrothermal Systems or Products of Recent Weathering

3.5 Heat Source for Onverwacht Hydrothermal Activity

3.6 Buck Reef Chert: Deposition During Hydrothermal or Normal Marine Conditions?

4 Hydrothermal Systems of the Fig Tree Group

4.1 Baryte

4.2 Hydrothermally Altered Shales and Sandstones

4.3 Bien Venue Massive Sulphide Deposit

4.4 Heat Source for Fig Tree Hydrothermal Activity

5 Implications of Hydrothermal Activity for Early Life in the Barberton Greenstone Belt

References

Birth of Biomolecules from the Warm Wet Sheets of Clays Near Spreading Centers

1 Introduction

2 The Primordial Womb Hypothesis

3 Background

3.1 Organic Geochemistry

3.2 Clay Minerals

3.3 Natural Clays in Hydrothermal Systems

4 Experimental Design for Evaluating the Role of Clay in Biosynthesis Reactions

4.1 Experimental Methods

4.2 Analytical Methods

4.2.1 Organic

4.2.2 Mineral

5 Results

5.1 Summary of Experimental Results

6 Discussion

6.1 Thermodynamic Analysis of the Hydrothermal Organic Synthesis Experiment

6.2 Reaction Pathways of the Hydrothermal Organic Synthesis Experiment

6.2.1 Early-Stage Reactions: Hydrogen Production

6.2.2 Late-Stage Reactions: Clay–Surface Interactions

6.2.3 Hydrogen Consumption in Montmorillonite-Containing Experiments

6.2.4 Oxidation State

7 Summary

references

Towards a Null Hypothesis for Stromatolites

1 Peculiar Contortions

2 Implications

References

Trace Element Geochemistry as a Tool for Interpreting Microbialites

1 Introduction

1.1 How Do Microbialites Form?

1.2 Biosignatures in Microbialites

2 Trace Element Geochemistry and Microbialites

2.1 The Use of Trace Elements to Help Reconstruct Environments of Deposition

2.2 Effect of Microenvironments on Trace Element Inventories

2.3 Bioactive Metal Accumulation

3 Diagenetic Disruption of Trace Metal Signatures

4 Outlook

5 Summary

References

A Modern Perspective on Ancient Life: Microbial Mats in Sandy Marine Settings from the Archean Era to Today

1 Introduction

2 Microbially Induced Sedimentary Structures – MISS

3 Modern MISS and Their Formation

4 Classification of MISS

5 How to Interprete Archean MISS by Using Modern Analogues of the Structures

6 Conclusive Remarks and the Question Which Microbiota Formed Microbial Mats in the Archean Era

References

Early Life Record from Nitrogen Isotopes

1 Introduction

2 Nitrogen in Rocks

3 Nitrogen Isotopes in Modern Marine Sediments: The Cycle

4 The Preservation of the Isotopic Signature of N in the Rock Record: The Role of Metamorphism and Alteration

5 The Significance of 15N-Depleted Nitrogen in Early Archean Organic Matter

6 Isotopic Shifts Recorded by N, C and Fe at Late Archean: A Reaction to the Progressive Oxygenation of the Earth

7 Enhanced Denitrification or N Imbalanced Fluxes in the Ocean as a Response to the Oxygenation of the Earth

8 Conclusions

References

Integration of Observational and Analytical Methodologies to Characterize Organic Matter in Early Archaean Rocks

1 Introduction

2 Geological Setting of the Warrawoona Group

2.1 Dresser Formation

2.2 Apex Basalt

3 Materials and Methodology

3.1 Organic Petrology

3.2 Electron Microscopy

3.3 C-Isotope Analysis

3.4 Total Organic Carbon (TOC) and Elemental Analysis

4 Results and Discussion

4.1 Dresser Formation Carbonaceous Matter

4.2 Apex Basalt Carbonaceous Matter

4.3 Elemental and Carbon Isotope Compositions of CM

5 Summary and Conclusions

References

Bugs or Gunk? Nanoscale Methods for Assessing the Biogenicity of Ancient Microfossils and Organic Matter

1 Introduction

1.1 Structure and Bonding of Kerogen

1.2 Abiotic Fischer-Tropsch-Type Carbonaceous Matter

1.3 Putative Archean Microfossils and Stromatolites from Western Australia

2 Methods

2.1 Samples and Standards

2.2 Sulfur Embedding and Ultramicrotomy

2.3 FTT Sample Preparation

2.4 Scanning Transmission X-ray Microscopy (STXM)

2.5 X-ray Absorption Near-Edge Structure Spectroscopy (XANES)

2.6 Tranmission Electron Microscopy (TEM)

2.7 Electron Energy-Loss Near-Edge Structure Spectroscopy (ELNES)

3 Results

3.1 Apex Carbonaceous Matter

3.2 Strelley Pool Carbonaceous Matter

3.3 Gunflint Kerogen

3.4 Fischer-Tropsch-Type Carbonaceous Matter

4 Discussion

4.1 Beam Damage of Carbonaceous Matter by STXM and TEM

4.2 Spectral Differences Between XANES and ELNES

4.3 Structure and Bonding of Precambrian Carbonaceous Matter

4.4 Comparison with FTT Carbonaceous Matter

4.5 Controversy Surrounding the Apex Microfossils

4.6 Controversy Surrounding the Strelley Pool Stromatolites

4.7 Archean Hydrothermal Microbial Communities

5 Summary

References

What Can Carbon Isotopes Tell Us About Sources of Reduced Carbon in Rocks from the Early Earth?

1 Introduction

2 Sources of Reduced Carbon and Their Isotopic Compositions

2.1 Biological Sources

2.2 Abiotic Sources

2.2.1 Exogenous Inputs

2.2.2 Endogenous Inputs

3 Carbon Isotopes and the Early Geologic Record

3.1 Isotopic Composition of Organic Matter Through Time

3.2 Reduced Carbon in Rocks from Southwest Greenland

3.3 Carbon Isotopes and Putative Microfossils in the Warrawoona Group

4 Concluding Remarks

References

Index