There is an unexplained terrestrial mass extinction at the Devonian-Carboniferous boundary (359 million years ago). The discovery in east Greenland of malformed land plant spores demonstrates that the extinction was coincident with elevated UV-B radiation demonstrating ozone layer reduction. Mercury data through the extinction level prove that, unlike other mass extinctions, there were no planetary scale volcanic eruptions. Importantly, the Devonian-Carboniferous boundary terrestrial mass extinction was coincident with a major climatic warming that ended the intense final glacial cycle of the latest Devonian ice age. A mechanism for ozone layer reduction during rapid warming is increased convective transport of ClO. Hence, ozone loss during rapid warming is an inherent Earth system process with the unavoidable conclusion that we should be alert for such an eventuality in the future warming world.

The latest Devonian to Mississippian interval records the long term transition from 12Devonian Greenhouse conditions into the Late Palaeozoic Ice Age (LPIA). This transition was 13 punctuated by three short glaciation events in the latest Famennian, mid Tournaisian and Viséan 14 stages respectively. Primary evidence for glaciation is based on diamictite deposits and striated 15 pavements in South America, Appalachia and Africa. The aim of this review is to assess the primary 16 biostratigraphical and sedimentological data constraining diamictite deposits through this transition. 17These data are then compared to the wider record of eustasy, mass extinction and isotope stratigraphy 18 in the lower palaeolatitudes. Precise age determinations are vital to integrate high and low 19 palaeolatitude datasets and to understand the glacial control on wider global changes. Palynological 20 techniques currently provide the best biostratigraphic tool to date these glacial deposits and to 21 correlate the effects of glaciation globally. This review highlights a high degree of uncertainty in the 22 known history of early LPIA glaciation as much of the primary stratigraphic data is limited and/or 23 unpublished. Future high-resolution stratigraphic studies are needed to constrain the history of 24 glaciation both spatially and temporally through the latest Devonian and Mississippian. 25 --26The latest Devonian to Mississippian time period saw the onset of the Late Palaeozoic Ice Age 27 (LPIA), marked by three short "precursor" glaciations in the latest Famennian, mid Tournaisian and 28Viséan respectively (Caputo et al. 2008; Montañez & Poulson 2010). In contrast, the earlier 29Devonian Period had globally warm climates, high sea levels and widespread reef complexes at 30 median palaeolatitudes (Copper 2002; Joachimski et al. 2009). The latest Devonian and 31Mississippian therefore record a transitionary period between these two first-order climate modes, 32 which was characterised by at least three distinct glacial episodes and long-term declining 33 atmospheric CO 2 concentrations (Berner 2006). Within this transitionary period are global oceanic 34 anoxic events associated with mass extinction, eustatic changes and isotopic excursions that 35 approximately coincide with the glaciations in the latest Famennian and mid Tournaisian (Caplan & 36 Bustin 1999; House 2002; Kaiser et al. 2007Kaiser et al. , 2008 Kaiser et al. , 2011 Kaiser et al. , 2015McGhee 2013; Sallan & 37 Coates 2010; Saltzman 2002;Streel 1986;Yao et al. 2015;). 38Evidence for LPIA glaciation in Gondwana is based on diamictite deposits and striated pavements in 39 both South America and Africa (Caputo et al. 2008;Isaacson et al. 2008). Recent work describing 40 latest Devonian diamictites in Appalachia also provides evidence for an additional glacial centre in 41 the low palaeolatitudes of Euramerica (Brezinski et al. 2008;. The precise age of these glacial 42 deposits is crucial in understanding the relationship between LPIA glaciation and it...

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