Experimental fossilization of early plant lipids — tracing incipient terrestrialization using a comparative approach with extant bryophytes and Cambrian-Silurian sediments

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The algae-to-plant transition and associated conquest of the continental realm was a complex process, enabled by evolutionary innovation of biochemical pathways. Amongst these are changes in the biosynthesis of terpenoids and other secondary metabolites that differ between algae and plants, and which may have been recorded in the rock record. Tracing the incipient terrestrialization process—i.e. its timing, mode, and extent—is of paramount importance for understanding larger Earth system changes across the terminal Neoproterozoic and early Paleozoic. Enhanced rates of carbon burial, changes in the marine redox structure, nutrient-modulated primary productivity and the explosive radiation of animals may all have been indirectly affected as a consequence of the conquest of land by the earliest plants. Tracing the oldest plants using the fossil record is complicated due to generally poor preservation in terrestrial environments, whilst early spores are exceedingly rare. Fossil lipids can offer a solution. Yet the molecular remnants of early-branching plants in earliest Paleozoic sedimentary deposits have thus far received insufficient attention, which is likely partially due to the fact that our knowledge of molecular signatures of these early phylogenetic branches spanning the algae-to-plant transition (i.e. charophytes, liverworts and bryophytes) is still sparse. Here I propose a dual approach, in which modern biomass of said species will be ‘artificially aged’ using pyrolysis and catalytic hydrogenation in order to obtain a better understanding of characteristic early plant biomarkers, whilst sedimentary rocks from three terrigenous-influenced sequences from Australia, spanning the Cambrian and Ordovician will be systematically studied in order to find any traces of the algae-to-plant transition. The outcomes of this study not only carry the potential to reveal evolutionary changes in terpenoid biosynthesis across the algae-to-plant transition, but may also shed more light on the incipient colonization of the terrestrial realm, thereby placing constraints on triggers, facilitators and global consequences.