PhD: When Bacteria Ruled the Earth (and Mars?): experimental insights into microbial palaeobiology and astrobiology

Summary
This project will deploy and develop cutting-edge experimental and micro-analytical techniques to elucidate the fossil record of ancient bacteria and other micro-organisms.

Project background
Micro-organisms like bacteria are far from "simple". They are the progenitors of all life on Earth and have driven profound changes on our planet for several billion years, transforming the chemistry of the oceans and atmosphere while becoming spectacularly diverse and abundant. To understand the origin, evolution, and ecological resilience of life on Earth, while gaining key "search images" to assist the search for life on Mars, we must explore the fossil record of ancient bacteria. But while the significance of fossil bacteria is widely acknowledged, even the best preserved examples are microscopic, morphologically ambiguous, and therefore difficult to interpret, fuelling major debates about the origins of important groups and their relationships to key events in Earth’s history. Recent advances in high-resolution analytical methods reveal the structure and composition of candidate fossil bacteria in unprecedented detail. To interpret these data correctly, we need to understand how bacterial remains actually decay, mineralize, mature, and metamorphose to produce the observable characteristics of fossils. This project will combine an experimental approach to palaeobiology with the study of important fossil materials spanning ~2 billion years, producing new insights into the microbial diversity of ancient ecosystems and facilitating the search for life on Mars.

Research questions
1. How can experimental approaches to the science of fossil preservation ("taphonomy") be adapted for bacteria and other micro-organisms?
2. How are the identifiable features of selected bacterial groups modified or lost during decay, mineralization, maturation and metamorphism?
3. How do differences in the cell structure and composition of diverse bacterial groups influence their potential to preserve as recognisable fossils?
4. How might the preservation of bacteria-like fossils on Mars differ from preservation on Earth, and what are the implications for forthcoming rover mission operations?
5. How do preservational factors influence our ability to distinguish between fossil bacteria and non-biological mineral structures, e.g., using morphometrics?

Methodology
This project will involve (a) experiments in the microbiology laboratory, (b) experiments using pressure and temperature to modify microbial remains in experimental samples and fossil materials, and (c) analytical work to characterise both experimental products and real fossil assemblages. Work in years 1–2 will concentrate on: (1) the analysis of important bacterial fossil assemblages using petrographic microscopy, SEM and spectroscopic techniques, and (2) preliminary experiments to establish baseline “decay series” for selected microbial groups (Research Question 1), and to refine laboratory and analytical methods for artificial decay, mineralization (encrustation and entombment by carbonate and silica), maturation (heat treatment and compression) and metamorphosis (piston cylinder experiments). In years 2–3+, these methods will be used to generate publishable datasets addressing the differential taphonomy of different microbial groups under different physicochemical conditions on Earth and Mars (Research Questions 2–4). Morphometric approaches will be developed to track the effects of fossilization on the position of microbial populations in morphospace and compare them with abiotic structures (Research Question 5).

Training
A comprehensive training programme will be provided comprising both specialist scientific training and generic transferable and professional skills. Practical training will be provided in geomicrobiological laboratory methods, experimental taphonomy, petrographic and microbiological microscopy, Raman spectroscopic microscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy, the use of the piston cylinder apparatus, and the statistical analysis of morphological and compositional data.

Requirements
This project would suit a geoscience or biology graduate with interests in the general area of palaeobiology, cell biology, mineralogy, and/or geochemistry. Experience in laboratory-based practical work would facilitate a quick start. However, all necessary training will be provided.