Astrobiology Science and Technology for Exploring Planets (ASTEP)

PI: Kirschvink, Joseph

Magnetofossils, the magnetic minerals left in the rock record by a variety of magnetotactic microbes, represent a largely untapped record of paleoenvironmental conditions and microbial paleoecology. Their presence can provide a new perspective on paleobiology and, thanks to distinctive microwave and magnetic properties, they can potentially be detected and identified in rocks more easily than other microbial fossils — perhaps even by an instrument on a planetary lander. The goal of our proposal is to build the fossil record of magnetotactic bacteria so that it can be used as a tool for understanding the evolution of life and the biosphere. We will use rock magnetism, ferromagnetic resonance spectroscopy (FMR), and tomographic transmission electron microscopy (TEM) to identify and characterize magnetofossils. FMR is sensitive to the presence of the chains of magnetic minerals produced by magnetotactic microbes, and tomographic TEM will enable us to construct three-dimensional images of magnetosome crystals.

We have three objectives that we seek to attain in reaching this goal. We will: 1) test the limits of FMR as a screening technique for samples likely to contain magnetofossils by applying it to Cenozoic samples known to contain magnetofossils in varying concentrations, as well in control samples of magnetosomes in salts diluted with other ferromagnetic materials, 2) survey a variety of carbonate rocks with microbiallygenerated textures from throughout Earth history for magnetofossils to extend understanding of the abundance of magnetofossils throughout geologic time, and 3) examine carbonate platform sediments from across the Cretaceous-Tertiary (K-T) and Permo-Triassic (P-T) boundaries for magnetofossils to study how the K-T and P-T crises affected microbial ecology.

The proposed work addresses two of the NASA strategic objectives in the domain of the Science Mission Directorate. Primarily, it will “explore the universe.” In particular, it meets one of the main goals of the Astrobiology Roadmap by developing techniques for identifying a biosignature that can “reveal and characterize past or present life in ancient samples from Earth [and] extraterrestrial samples measured in situ.” The application of this biosignature can address several of the goals of the Exobiology and Evolutionary Biology Program. Specifically, the magnetofossil record should be able to provide insights into aspects of the early evolution of Earth’s biosphere, including the history of major biogeochemical cycles, particularly those of iron and oxygen, and the response of Earth’s biosphere to mass extinction events. It should also provide insights into the evolution of biomineralization, a trait more common in “advanced” life. In addition, the FMR techniques developed in this work may potentially be applied in a robotic planetary lander mission and contribute to the strategic objective of “conduct[ing] robotic exploration of Mars to search for evidence of life.”