Mass-extinction events in Earth history can provide us with crucial baselines by which ongoing biodiversity loss can be compared and its selectivity calibrated. All mass-extinction events are connected to periods of strong perturbations of the carbon cycle, including changes in greenhouse gas concentrations in the atmosphere and associated global warming/cooling. These major changes in the carbon cycle are thought to be driven by interconnected episodes of widespread volcanism, rapid increase or burning of biomass, burial, erosion or oxidation of carbon, destabilization of methane from the sea-floor and permafrost, and marine anoxia. A recently discovered phenomena associated with mass-extinction events are an increase of teratological microfossils (pollen, spores, organic-walled phyto- and zooplankton) with aberrations in morphology and texture. These malformed fossils allow us to make direct inferences about the proximate mechanisms behind these biotic crises. Unique in the fossil record, these tell-tale signatures occur in both the marine and terrestrial realms.

With this interdisciplinary project we aim to test a set of interrelated hypotheses that link malformation to either metal toxicity (Hg, Cd, Ni, Pb), or increased UV-B radiation due to ozone loss, or to environmental stress related to climate change. Here, we propose to use these microfossils and their modern analogues in experimental and field settings to explore the true potential of teratology as a proxy to test, integrate and refine the many existing models for biotic crises across time and space. The deep time perspective is provided by subprojects led by Ghent University and Utrecht University working on Palaeozoic and Mesozoic events characterized by the presence of abundant malformed microfossils reflecting both marine and terrestrial ecosystems. These work packages will tease out the relative influence of metal toxicity related to marine anoxia and volcanic activity from geochemical and micropaleontological analyses of core and outcrop material complemented by studies of modern analogs. Work packages performed at UC Berkeley and University of Nottingham will focus on the role of UV-B radiation and ground-truth observations from deep time via growth experiments using nearest living equivalents that arerepresentative of the projects performed at UGent and UU.