Modern-day ocean circulation behaves as a complex forced convective system that is characterized by the decrease in water temperature but increase in water density with depth. The dissolved oxygen content – which initially decreases due to biological oxygen demand – also increases with depth. In contrast to the present-day scenario, we propose that during the Archaean and Proterozoic eons inverted profiles could have developed such that, with depth, ocean water temperature increased and density and dissolved oxygen decreased. These inverted temperature and density profiles resulted in palaeo-ocean circulation behaving as a free convective system. It is proposed that this free convection, which may have been stable, or chaotic and subject to secondary instabilities, hindered the deep oxygenation of the palaeo-ocean. It may not be coincidental that the great oxygenation event (GOE) and Huronian glaciations are contemporaneous, in a similar way that the Neoproterozoic oxygenation event (NOE) is known to have been associated with glaciations. The global-scale external forcing required to switch the natural convective system to its present-day configuration is suggested to have been associated with Neoproterozoic glaciations and the subsequent lowering of ocean water salinity that accompanied them. We propose that this inverted the ocean water density gradient, allowing the oxygenation of the oceans for the first time. It is beyond the scope of this work to model the complex natural convection system, but we hope that geophysicists and numerical modellers will quantitatively evaluate the hypothesis proposed here to validate or refute our proposition.

Cadmium sulfide mineralization occurs in grey-black shales of the late Mesoproterozoic Stoer Group, Torridonian Supergroup, northwest Scotland. Cadmium is strongly redox-controlled, and normally concentrated in anoxic marine sediments or epigenetic mineralization involving organic matter. However the Stoer Group was deposited in a terrestrial environment, including lacustrine deposits of shale. At the limited levels of atmospheric oxygenation in the Mesoproterozoic (∼10% of present), the near-surface environment could have fluctuated between oxic and anoxic, allowing fractionation of Cd from Zn, and the formation of Cd sulfide rather than Cd-bearing sphalerite. This occurrence emphasizes the importance of the Stoer Group as a record of the Mesoproterozoic terrestrial environment.

The generation of organic matter from CO2 and H2O is a highly endothermic reaction. Energy for biological carbon fixation can be derived from chemical potential gradients in the environment by chemoautotrophic organisms or it can be harvested from photon energy by photosynthesis. On Earth, the plate tectonically driven carbon flux through the surface environment is of such a magnitude that the chemical free energy production within the Earth is insufficient to support conversion of any significant fraction of the carbon to organic matter through chemoautotrophy. Therefore, the chemical and isotopic fingerprints we observe in the Earth's surface environments are based on the invention of photosynthesis by life. We cannot a priori assume that life on any planet will invent photosynthesis and remote life detection should thus not be based exclusively on the expectations from our own ecosystem.

Background and aim This study assessed the accuracy of using capnography with a modified, hollow gum elastic bougie in predicting tracheal intubation, and its effectiveness as a method of apnoeic oxygenation.

Methods Patients were randomly allocated to having the gum elastic bougie inserted, under anaesthesia, in the trachea or the oesophagus. End-tidal carbon dioxide measurements were made at 10 and 20 s. The position of the gum elastic bougie was correctly predicted in 89.2% of patients. We tested the apnoeic oxygenation on an anaes-hetic simulator model, which is housed in the Scottish Anaesthesia Simulator Centre, Stirling, UK.

Results The time taken for the oxygen saturation to fall to 90% was significantly prolonged when the gum elastic bougie was used for apnoeic oxygenation.

Conclusion The modification of the gum elastic bougie allows a more objective assessment of correct placement than the previous tactile method. The current design of bougie is unsuitable but can be modified.

The recent experimental results obtained for c-axis oriented YBaCuO thin films deposited at the optimized conditions for the microwave applications are presented and discussed. The emphasis is on the study of the relationship between oxygen profiles, crystallographic structure and electrical and physical properties of the films formed in situ at the same and optimized conditions of sample deposition and further submitted to the different conditions of sample cooling. The studies of the oxygen depth concentration profiles and of the oxygen contents are carried out using the recently developed Nuclear Reaction Analysis (NRA). These results are correlated, on one hand, with the measurements of the atomic composition and structure by RBS, XRD and TEM and, on the other hand, by the measurements of the electrical and physical properties Tc, Jc and microwave surface resistance Rs. All results are consistent with the idea that the fully oxygenated films are formed during in situ growth at T∼ 700°C. For T< 300°C, the oxygen interface transfer coefficient is very small and the oxygen content is practically preserved. However a large room temperature oxidation (corrosion like) takes place in the presence of water vapor. The fundamental and applied consequences of these findings for the mechanism of thin films growth and for the properties of the films in the presence of cathodic plasma or laser plume are analysed.