When did life first appear on Earth and what form did it take? The answer to this intriguing and fundamentally important question lies somewhere within the early Archean rock record. The young Earth was, however, a very different place to that we know today and numerous pitfalls await our interpretation of these most ancient rocks.
The first half of this practical guide Early Life on Earth equips the reader with the background knowledge to successfully evaluate new potentially biological finds from the Archean rock record. Successive steps are covered, from locating promising samples in the field, through standard petrography and evaluation of antiquity and biogenicity criteria, to the latest state of the art geochemical techniques. The second half of the guide uniquely brings together all the materials that have been claimed to comprise the earliest fossil record into an easily accessible, fully illustrated format.
Early Life on Earth will be a handbook that every Archean geologist, palaeobiologist and astrobiologist will wish to have in their backpack or on their lab-bench.
Setting the scene, an introduction by Martin Brasier
Milestones in the search for early life on Earth The Eozoon debate and the 'Foraminosphere'
The Cyanosphere, phase 1
The Cyanosphere, phase 2
PART A: Investigating life in early Archean rocks
1. What can we expect to find in the earliest rock record?
1.1. Body fossils
1.2. Trace fossils
1.3. Chemical fossils
2. The difficulties of decoding early life
2.1. Non-biological artefacts
2.2. Post-depositional contamination
2.3. The pros and cons of the 'Principle of Uniformity'
2.4. A benchmark for microfossils and stromatolites
3. Establishing the criteria for early life on Earth
3.1. Antiquity criteria
3.1.1. General antiquity criteria
3.1.2. Additional antiquity criteria specific to microfossils
3.1.3. Additional antiquity criteria specific to trace fossils
3.2. Biogenicity criteria
3.2.1. General biogenicity criteria
3.2.2. Additional biogenicity criteria specific to microfossils
3.2.3. Additional biogenicity criteria specific to trace fossils
3.3. The problem of stromatolites
4. Fulfilling the criteria for early life on Earth
4.1. Where to look? -- Archean cratons
4.1.1. Geology of the Pilbara craton
4.1.2. Geology of the Barberton greenstone belt, Kaapvaal craton
4.1.3. Geology of southwest Greenland
4.2. Typical rocks found in the early Archean that could host life
4.2.2. Pillow basalt
4.2.4. Hydrothermal deposits
5. Techniques for investigating early life on Earth
5.1. Geological mapping
5.2. Radiometric dating
5.3. Optical microscopy
5.4. Scanning electron microscopy (SEM)
5.5. Transmission electron microscopy (TEM)
5.6. Secondary ion mass spectrometry (SIMS and NanoSIMS)
5.7. Laser-Raman micro-spectroscopy
5.8. Near edge x-ray absorption fine structure spectroscopy (NEXAFS) and electron energy loss spectrometry (EELS)
5.9. Synchrotron x-ray tomography
5.10. Atomic force microscopy (AFM)
5.11. Molecular fossils
5.12. Carbon isotopes
5.13. Sulphur isotopes
5.14. Other isotopic systems
Summary of techniques
Part B: An atlas of claims for early Archean life
1. >3700 Ma, Isua Supracrustal Belt and Akilia Island, S.W. Greenland
2. #3490 Ma, Dresser Formation, East Pilbara, Western Australia Summary of claims for early life from this Formation
3. #3470 Ma, Mount Ada Basalt, East Pilbara, Western Australia
4. #3460 Ma, Apex Basalt, East Pilbara, Western Australia
5. #3450 Ma, Hoogenoeg Formation, Barberton, South Africa
6. #3450 Ma, Panorama Formation, East Pilbara, Western Australia
7. #3400 Ma, Strelley Pool Formation, East Pilbara, Western Australia
Summary of claims of early life from this Formation
8. #3416-3334 Ma, Kromberg Formation, Barberton, South Africa
9. #3350 Ma, Euro Basalt, East Pilbara, Western Australia
10. #3250 Ma, Fig Tree Group, Barberton, South Africa
11. #3240 Ma, Kangaroo Caves Fm., East Pilbara, Western Australia
12. #3200 Ma, Moodies Group, Barberton, South Africa
13. #3200 Ma, Dixon Island Formation, West Pilbara, Western Australia
14. #3000 Ma, Cleaverville Formation, West Pilbara, Western Australia
15. #3000 Ma, Farrel Quartzite, East Pilbara, Western Australia
16. The Imposters. Younger biological contaminants and non-biological artefacts
David Wacey is a University Research Fellow at the University of Western Australia in Perth. He graduated with honours from Oxford University in 1998 and then undertook a D.Phil. investigating the geochemistry and microbiology of modern and ancient dolomite formation. It was during this time that he became interested in primitive microbes and how the earliest life on Earth may have arisen and evolved. On completion of his D. Phil he decided to concentrate his research on the earliest rocks found on Earth. After 12 years at Oxford he relocated to Western Australia where he now works on a number of problems relating to the recognition and understanding of the earliest signs of life of Earth.
"Suitable for graduate students and early career researchers, this book provides a useful introduction to the current understanding of life on the early Earth. The excellent images and use of bullet points and tables to encapsulate key information make this book highly readable [...] providing suggestions for additional reading for those who want (or need) to know more. The text is clear and well-written [...] . This book is thought-provoking [...] ."
– Alison J. Wright, The Astrobiology Society of Britain, September, 2009
"Wacey [...] has chosen a daunting task: to review everything more than three billion years old that anyone has interpreted as a body, trace, or chemical remnant of life on Earth. [...] At approximately 100 pages, this overview is quite succinct, yet well illustrated and comprehensively referenced. [...] Pound for pound, this may be the best available summary of evidence of Earth's earliest life [...] a good introduction for nonspecialists. Summing Up: Highly recommended. Upper-division undergraduate through professional collections."
– B. M. Simonson, Choice, Vol. 47 (3), November, 2009
"Gives the reader a general overview of early-life studies [...] . The topics are presented in such a way that even a non-scientist would be able to grasp most of the basic concepts. [...] The topics covered are well-organized and clearly explained, and each section is followed by extensive lists of references for further reading. I would certainly use this book as the basis of an introductory course curriculum at the upper undergraduate or graduate level."
– Dina M. Bower, Geologos, Vol. 16 (3), September, 2010