Abstract The Late Jurassic Slottsmøya Member Lagerstätte on Spitsbergen offers a unique opportunity to study the relationships between vertebrate fossil preservation, invertebrate occurrences and depositional environment. In this study, 21 plesiosaurian and 17 ichthyosaur specimens are described with respect to articulation, landing mode, preservation, and possible predation and scavenging. The stratigraphic distribution of marine reptiles in the Slottsmøya Member is analysed, and a correlation between high total organic content, low oxygen levels, few benthic invertebrates and optimal reptile preservation is observed. A new model for 3D preservation of vertebrates in highly compacted organic shales is explained. Supplementary material: A taphonomic description of each marine reptile specimen is available at https://doi.org/10.6084/m9.figshare.c.2133549

This is a commentary on the preceding chapter by Ohmoto et al., in which it is suggested that oxygen concentrations have been high throughout Earth history. This is a contentious suggestion at odds with the prevailing view in the field, which contends that atmospheric oxygen concentrations rose from trace levels to a few percent of modern-day levels around 2.5 b.y. ago. This comment notes that many of the data sets cited by Ohmoto et al. as evidence for a relatively oxidized environment come from deep-ocean settings. This presents a possibility to reconcile some of these data and suggestions with the overwhelming evidence for an atmosphere free of oxygen at that time. Specifically, it is possible that deep-ocean waters were relatively oxidized with respect to certain redox pairs. These deep-ocean waters would have been more oxidized than surface waters, thus representing an “upside-down biosphere,” as originally proposed 25 years ago by Jim Walker.

This review summarizes and assesses a series of papers presented at the Geological Society of America Annual Meeting in 2011 on the changing composition of Earth's early atmosphere. This is a developing field, with differing views, due largely to the facts of an incomplete rock record and negligible preservation of the gaseous components of the atmosphere. Nevertheless, there are constraints, available through geological proxies in the form of chemical sedimentary rocks that reflect the composition of the hydrosphere, and because the two are directly linked, the atmosphere. A review of the geological constraints on atmospheric conditions is presented for early Earth, from its formation at 4.56 Ga up to 1.8 Ga, followed by a developing model that links changing atmosphere/hydrosphere conditions and biosphere evolution to changes in planetary tectonics, including the evolving supercontinent cycle.