NEOEARTH: MSCA Individual Fellowship to Andrew Merdith Funded by the European Commission 2021-2023
Summary.
The evolution of the first animals during the late Neoproterozoic Era was a critical step in Earth history. Animals revolutionised global biogeochemistry, and their complex (and later motile) forms ultimately allowed for the evolution of intelligence. Because animals require oxygen, it is commonly believed that the emergence of the first animals around 570 Million years ago (Ma) was triggered by rising levels of dissolved oxygen in the upper ocean, driven by an increase in atmospheric O2. However, this theory is controversial, because there are no geological archives that can directly constrain atmospheric oxygen concentration, and marine sedimentary records can only record the local conditions at the seafloor. The late Neoproterozoic is also a time of dramatic climate change, recording two low latitude ‘Snowball Earth’ glaciations, which themselves may have contributed to both the rise of O2 and the evolution of complex life. Understanding the global environmental change during the late Neoproterozoic requires a synthesis of data and computer modelling. Here, biogeochemical models of the atmosphere and marine environment can be used to estimate global surface temperature and oxygen levels, and crucially, can also then attempt to reproduce the marine sedimentary record to be validated against the available geochemical data. This approach has several advantages over trying to ‘invert’ the sparse sedimentary data into water column and atmospheric concentrations. However, a global biogeochemical model of the Neoproterozoic Earth is not currently possible because the underlying tectonics that must drive the model are not well known.
Plate tectonics, the tessellation of the Earth’s lithosphere into discrete, semi-rigid plates that interact along mid-ocean ridges, subduction zones and transform boundaries, is a unifying theory of Earth sciences. In our solar system, plate tectonics is unique to Earth and a key to the existence of life. However, the fifty-year-old theory falls short in explaining how the hydrosphere, atmosphere and biosphere interact with the coupled non-linear evolution of the plate-mantle system. Instead, it provides a foundation that can be extended to understand feedbacks between solid Earth evolution and these surface systems, allowing reconstruction of surface conditions that facilitates the testing of hypotheses against the limited available geochemical proxies. Recent advancements in plate tectonic modelling have provided time sensitive palaeo-tectonic-geography maps back to 1 Ga , allowing us for the first time to quantitatively analyse the relationship between whole Earth systems in the Neoproterozoic (NEOEARTH) in a manner that is grounded in observational and analytical geology and geophysics. Using these models as a foundation, we propose to quantify key tectonic parameters—CO2 degassing, ridge spreading rates, palaeotopography, palaeogeography, and palaeobathymetry—of the Ediacaran Earth as a set of boundary conditions for biogeochemical and climate modelling. Outputs from the model will interrogate possible tectonic drivers for two key events: the Marinoan glaciation and the Neoproterozoic oxidation event.
