Geobiology and the fossil record: eukaryotes, microbes, and their interactions

Abstract

Geobiology attempts to understand the interactions between Earth and the life which has evolved on it. It is an all-encompassing field that embraces both living systems on Earth as well as an understanding of the history of these systems since life first evolved. The fossil record and associated geological and geochemical data provide a major avenue towards understanding the evolution of geobiological systems. Among the many new and exciting directions of research for geobiology, a particularly fertile field is represented by studies of the various interactions between eukaryotes and microbes that can be detected through examination of the fossil record. For example, such interactions include the various roles which microbes play in taphonomy and preservation of eukaryotes as fossils, particularly cases of exceptional fossil preservation. Similarly, recognition of microbially induced sedimentary structures (MISS) in siliciclastic sediments has been a subject of significant recent interest. Documentation of MISS has led to a greater understanding of the role of microbial mats in providing a distinctive structure to marine subtidal seafloors, which has fostered studies of benthic eukaryote adaptations to such mat-dominated environments. The continued evolution of bioturbation in the Cambrian led to elimination of microbial mats on shallow subtidal seafloors, causing evolutionary and ecological changes in eukaryotes adapted to living on and in seafloors structured by such mats. Studies of these changes, termed the “Cambrian substrate revolution”, have been documented for a variety of echinoderms, molluscs, and trace fossils, and are some of the first to illuminate ecological interactions between eukaryotes and microbes through study of the fossil record. This new awareness which geobiology represents has begun to produce a whole host of approaches that causes researchers in the laboratory of the molecular or microbiologist to interact with those from the laboratory of the geochemist as they are led on a field trip by the palaeontologist exploring some fundamental issue in the history of life. Such interactions are not only important for considerations of life on Earth, but provide a framework for the search for life that may have once existed on other planetary bodies, such as Mars. Data from deep time and hence the fossil record plays a central role in such research, and thus geobiology opens up vast new research opportunities for palaeontology.