Visual Observation Of Lightning Propagation

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/62577/1/322215a0.pd

Lightning-Induced Reduction of Phosphorus Oxidation State

Phosphorus is frequently the limiting nutrient in marine and terrestrial ecosystems, largely owing to its poor solubility and slow movement through the rock cycle1, 2. Phosphorus is viewed to exist in geological systems almost exclusively in its fully oxidized state as orthophosphate. However, many microorganisms use the partially oxidized forms—phosphite and hypophosphite—as alternative phosphorus sources3, 4, 5, and genomic evidence suggests that this selectivity is ancient6. Elucidating the processes that reduce phosphate is therefore key to understanding the biological cycling of phosphorus. Here we show that cloud-to-ground lightning reduces phosphate in lightning-derived glass compounds, termed fulgurites. We analysed the phosphorus chemistry of ten fulgurites retrieved from North America, Africa and Australia, using microprobes and 31P nuclear magnetic resonance. Half of the fulgurites contained reduced phosphorus, mainly in the form of phosphite. The amount and type of reduced phosphorus was dependent on the composition of the fulgurite section examined: carbon-rich sections contained around 22% reduced phosphorus in the form of iron phosphide, whereas other fulgurites contained between 37 and 68% in the form of phosphite. We suggest that lightning provides some portion of the reduced phosphorus used by microbes, and that phosphate reduction by lightning can be locally important to phosphorus biogeochemistry

Natural Glasses

International audienceNatural glasses have been used since prehistoric times and are strongly linked to human evolution. On Earth, glasses are typically produced by rapid cooling of melts, and as in the case of minerals and rocks, natural glasses can provide key information on the evolution of the Earth. However, we are aware that natural glasses are products that are not solely terrestrial and that the formation mechanisms give rise to a variety of natural amorphous materials. On the Earth's surface, glasses are scarce compared to other terrestrial bodies (i. e., the Moon), since the conditions on the surface give rise to devitrification or weathering. In order to provide an exhaustive overview, we shall classify natural glasses based on the mechanisms by which they were formed: temperature related, temperaturepressure related, temperature-pressure-volatile related, and others. In this chapter, we will review the most common natural glasses and their technological applications and also the scientific and technological advancements achieved from the study of these natural amorphous materials. Finally, we will provide some insights into the structure and properties of natural glasses and melts