The Hidden Majority: Reading and Writing the Bacterial Fossil Record

Bacteria rule the Earth. Over billions of years, these fantastically diverse and abundant organisms have established and maintained Earth's nutrient cycles, infused the oceans and atmosphere with oxygen, and formed, shaped and weathered rocks and minerals. Even today, they are the true foundation of our biosphere. But fossil bacteria are tiny, ambiguous, often poorly preserved, and therefore challenging to study. Now, for the first time, new technology is beginning to reveal their secrets. Advances by our research group and others provide tantalising new data about the structure and make-up of fossil bacteria, but the interpretation of these data is vexed by uncertainties about the processes of decay and mineralization (fossilization) that ultimately produced them. Our work to decode fossil bacteria will reduce these uncertainties and thereby advance major debates about the origins of important groups and their relationships to key events in Earth's history.

Firstly, by showing experimentally how selected, ecologically important groups of bacteria are broken down and replaced or encrusted by minerals in the laboratory (making "artificial fossils"), we will discover new clues that palaeontologists can use to recognise these groups in the fossil record. This in turn will advance the study of ancient ecosystems and environments.

Secondly, we will combine these experimental insights with sophisticated chemical microscopy to update our understanding of some of the best preserved fossil bacteria known to science, which occur in the Rhynie chert in Scotland. These world-famous rocks open a spectacular window onto life on land 400 million years ago, including some of the oldest well preserved land plants and diverse bacteria. We will conduct a high-resolution census of Rhynie chert bacterial diversity, testing hypotheses about microbial life during the greening of the land. For example, many of the filament-shaped bacteria have been identified as (oxygen-making)...