Now that 2022 is nearly 60% complete it seemed past time to update my blog with some recent publications. So far this year my work has continued to focus on major topics in astrobiology: the origin of life, habitability, and the recognition of “false positives” in the search for life on Mars.
At the beginning of the year, Springer released a new volume titled Prebiotic Chemistry and the Origin of Life, which I co-edited with Anna Neubeck. Taken together, the chapters in this book provide a broad overview of the origin and evolution of life on Earth from a chemical and biological perspective, beginning with astrochemistry and ending with the origin of eukaryotes. The book should be readable for graduate students and researchers in the Earth, life and space sciences and is available here.
I also teamed up with Julie Cosmidis at Oxford to write False biosignatures on Earth and Mars, a review published by the Journal of the Geological Society of London. This review is something of a manifesto for the research we think needs to be done in the coming years to put the search for life on Mars on a sounder theoretical footing. The review summarises known processes that could have generated false biosignatures on early Mars. These examples are known largely from serendipitous discoveries rather than systematic research and remain poorly understood; they probably represent only a small subset of relevant phenomena. The review is available open access here.
Importantly, the processes that give rise to false biosignatures tend to be driven by kinetic processes similar to those that can actually give rise to, and support, life! Rocks that formed on the early Earth, close to the origin of life in time, space, and environmental conditions, may contain all kinds of things that formed abiotically but are now indistinguishable from traces of life. To make this point as clearly as possible to palaeontologists, I worked with Sean Jordan, now at the Instituto Superior Técnico, Lisbon, to write a short perspective piece for Nature Ecology and Evolution called A fundamental limit to the search for the oldest fossils. This can be read here.
I’ve also been pleased to work with Joel deWitt, a radiation physicist at East Carolina University, to answer a physics question that’s bugged me for years. The question is this: when uranium and other radioactive elements in rocks underground interact with water, how much radiation reaches the water? This is important because radiation can break water molecules apart to release hydrogen, which is then available as a fuel source to power microorganisms that live underground. There are ecosystems in the Earth’s crust that survive this way. The answer depends on the grain size of the rock, since larger grains attenuate more radiation. We show how to model this process in The Effect of Grain Size on Porewater Radiolysis, published in the AGU journal Earth and Space Science. The article is available open-access here.