Fossilized microorganisms in volcanic rocks from sub-seafloor environments

Abstract: Fossilized microorganisms are focused in this thesis. Such organisms have been observed in drilled basalt samples from the Emperor Seamounts in the Pacific Ocean collected during ODP (Ocean Drilling Program) Leg 197. The fossilized microorganisms occur in veins where they are attached to the vein walls of altered basalt, volcanic glass or zeolites and entombed in secondary mineral phases like calcite, aragonite and gypsum. The fossilized microorganisms consist of various morphological types: sheaths, segmented filaments, twisted filaments, amorphous filaments and branched filaments. Fossilized cells are also found in association with the filaments as well as microbially produced tunnel structures.The work has mainly been divided in two parts: (1) proving biogenicity of the microfossils and (2) studying the paleoenvironment that prevailed while the microorganisms lived, as well as the interaction between the microorganisms and their environment. The first part has been focused on various instruments and methods with the aim of gathering as much data as possible regarding the biogenicity of the microfossils. The methods that have been used are ESEM/EDS, ToF-SIMS, Raman spectroscopy, laser ablation ICP-MS and staining with the pigment PI (propidium iodide) in combination with fluorescence light. The use of these methods have resulted in various data that, when combined, display a strong case for the biogenicity of the microfossils.The second part has been focused on the minerals in which the microfossils are preserved as well as mineral phases closely associated with the microfossils. Studying fluid inclusions present in the same minerals that the microfossils are found in has made it possible to reconstruct the conditions that prevailed at the moment of preservation regarding fluid composition, fluid temperatures and water depth. With laser ablation ICP-MS it has been possible to study micro-scale variations in iron isotopes within the microfossils and to indicate iron fractionation that has taken place during the involvement in iron oxidation reactions and precipitation of iron oxides. Association with various minerals and alteration products has shown that the microorganisms have been able to inhabit various mineral surfaces and micro-environments as the alteration of the ocean crust has proceeded and the conditions for a biosphere have changed. The work extends the present knowledge about the deep-sub-seafloor biosphere and shows that it probably inhabits much larger volumes of the ocean crusts around the world than was previously known. The work introduces new geological niches and new micro-structures to search for and to study in the ongoing search for traces of life in geological environments. This has implications for the exploration of the ocean crusts and sub-surface environments on Earth as well as future exploration for a fossil record on other planetary bodies like Mars.