Earth terraformed: effects of landscape and critical zone evolution during Palaeozoic terrestrialization

To what extent are Earth’s surface mechanisms biological phenomena? Processes such as water movement, sediment deposition and weathering are well understood from a physical and chemical perspective, but the landforms and landscapes that they generate were more than a passive stage-set in the theatre of evolution. Today the presence of plants and animals can modify and regulate surface processes and so the first organisms to colonize the land would have inhabited lifeless terrains unfamiliar to the modern eye. The activity of these organisms and their descendants, variably stabilizing the land surface, altering the propensity of weathering, and corralling and regulating waterways, would have terraformed Earth’s continents, generating new habitats and creating ecological opportunities and challenges throughout the evolving biosphere. Only by understanding the big picture effects of terrestrialization over geological timescales can we understand how unique Earth’s surface is amongst rocky planets and recognise the importance of plants and animals in shaping modern landscapes and ancient geological resources. Until now, however, several knowledge gaps have endured: uncertain timelines for terrestrialization persist due to a patchy body fossil record, the role of life in modern geomorphic processes is often underdetermined due to the finite historicity of instrumental records and problems of isolating specific causes, and teleconnections between evolutionary effects have been understudied. At the same time, a wealth of pertinent subsurface and outcrop geological evidence remains underutilized. We will resolve these problems and deliver evidence for the impacts of evolutionary terraforming on landscapes, evolutionary trajectories, and sedimentary geological phenomena, by utilizing recent theoretical and technological advances in which we have been heavily involved. The project will holistically interrogate multi-scale records of life-sediment interactions including the near-instantaneous modification of sediment grains, the life-span interactions between individual organisms and landforms, the centennial and longer interactions between communities and landscapes, the multi-millennial recycling of previously altered sediment, and the evolution of such phenomena over geological timescales. By focussing on the Silurian to Carboniferous interval, we will capture samples dating from the time of nascent plant and infaunal communities to that of well-developed forests and diverse burrowers. Stepwise stratigraphic variation in properties coeval with terrestrialization phase will be calibrated by analysing palaeoecological data relative to the timescales over which they accrued. Further, we will ascertain how evolutionary changes in marine settings were contingent on terraforming modifications in linked upstream settings. The case studies are selected primarily from the well-dated UK geological outcrop and subcrop record which is shown to be a globally exceptional record of Silurian-Carboniferous non-marine strata, but which has never been systematically interrogated within a modern framework considering bio-sedimentary influences and the time significance of strata. Our objectives are to establish a timeline of terraforming, shedding light on the mechanics of one of the most crucial episodes of Earth history, and to disentangle abiotic-biotic cause and effect relationships at multiple focal lengths. Meeting such objectives is essential to present-day predictions of the effects of vegetation introduction or removal on river morphodynamics, flooding and groundwater table, or how changes in terrigenous sediment flux can impact marine communities. An additional practical benefit of the research will be a better understanding of the evolution of regional subsurface stratal geometries through the UK Palaeozoic, shedding new light on potential targets for geothermal energy exploration, carbon capture, and deep geological waste disposal.