Photochemistry is a fundamental process of planetary atmospheres that regulates the atmospheric composition and stability1. However, no unambiguous photochemical products have been detected in exoplanet atmospheres so far. Recent observations from the JWST Transiting Exoplanet Community Early Release Science Program2,3 found a spectral absorption feature at 4.05mum arising from sulfur dioxide (SO2) in the atmosphere of WASP-39b. WASP-39b is a 1.27-Jupiter-radii, Saturn-mass (0.28MJ) gas giant exoplanet orbiting a Sun-like star with an equilibrium temperature of around 1,100K (ref.4). The most plausible way of generating SO2 in such an atmosphere is through photochemical processes5,6. Here we show that the SO2 distribution computed by a suite of photochemical models robustly explains the 4.05-mum spectral feature identified by JWST transmission observations7 with NIRSpec PRISM (2.7sigma)8 and G395H (4.5sigma)9. SO2 is produced by successive oxidation of sulfur radicals freed when hydrogen sulfide (H2S) is destroyed. The sensitivity of the SO2 feature to the enrichment of the atmosphere by heavy elements (metallicity) suggests that it can be used as a tracer of atmospheric properties, with WASP-39b exhibiting an inferred metallicity of about 10* solar. We further point out that SO2 also shows observable features at ultraviolet and thermal infrared wavelengths not available from the existing observations.

Microalgal photosynthesis is responsible for nearly half of the CO2 annually captured by Earth's ecosystems. In aquatic environments where the CO2 availability is low, the CO2-fixing efficiency of microalgae greatly relies on mechanisms - called CO2-concentrating mechanisms (CCMs) - for concentrating CO2 at the catalytic site of the CO2-fixing enzyme ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco). While the transport of inorganic carbon (Ci) across membrane bilayers against a concentration gradient consumes part of the chemical energy generated by photosynthesis, the bioenergetics and cellular mechanisms involved are only beginning to be elucidated. Here, we review the current knowledge relating to the energy requirement of CCMs in the light of recent advances in photosynthesis regulatory mechanisms and the spatial organization of CCM components.

Photosynthetic organisms frequently experience abiotic stress that restricts their growth and development. Under such circumstances, most absorbed solar energy cannot be used for CO2 fixation and can cause the photoproduction of reactive oxygen species (ROS) that can damage the photosynthetic reaction centers of PSI and PSII, resulting in a decline in primary productivity. This work describes a biological "switch" in the green alga Chlamydomonas reinhardtii that reversibly restricts photosynthetic electron transport (PET) at the cytochrome b(6)f (Cyt b(6)f) complex when the capacity for accepting electrons downstream of PSI is severely limited. We specifically show this restriction in STARCHLESS6 (sta6) mutant cells, which cannot synthesize starch when they are limited for nitrogen (growth inhibition) and subjected to a dark-to-light transition. This restriction represents a form of photosynthetic control that causes diminished electron flow to PSI and thereby prevents PSI photodamage but does not appear to rely on a Delta pH. Furthermore, when electron flow is restricted, the plastid alternative oxidase (PTOX) becomes active, functioning as an electron valve that dissipates some excitation energy absorbed by PSII and allows the formation of a proton motive force (PMF) that would drive some ATP production (potentially sustaining PSII repair and nonphotochemical quenching [NPQ]). The restriction at the Cyt b(6)f complex can be gradually relieved with continued illumination. This study provides insights into how PET responds to a marked reduction in availability of downstream electron acceptors and the protective mechanisms involved.

Haldane's Dilemma refers to the concern that the need for many "selective deaths" to complete a substitution (i.e. selective sweep) creates a speed limit to adaptation. However, discussion of this concern has been marked by confusion, especially with respect to the term "substitution load". Here we distinguish different historical lines of reasoning, and identify one, focused on finite reproductive excess and the proportion of deaths that are "selective" (i.e. causally contribute to adaptive allele frequency changes), that has not yet been fully addressed. We develop this into a more general theoretical model that can apply to populations with any life history, even those for which a generation or even an individual are not well defined. The actual speed of adaptive evolution is coupled to the proportion of deaths that are selective. The degree to which reproductive excess enables a high proportion of selective deaths depends on the details of when selection takes place relative to density regulation, and there is therefore no general expression for a speed limit. As proof of principle, we estimate both reproductive excess, and the proportion of deaths that are selective, from a dataset measuring survival of 517 different genotypes of Arabidopsis thaliana grown in eight different environmental conditions. These data suggest that a much higher proportion of deaths contribute to adaptation, in all environmental conditions, than the 10% cap that was anticipated as substantially restricting adaptation during historical discussions of speed limits.

Subduction of hydrous and carbonated oceanic lithosphere replenishes the mantle volatile inventory. Substantial uncertainties exist on the magnitudes of the recycled volatile fluxes and it is unclear whether Earth surface reservoirs are undergoing net-loss or net-gain of H2O and CO2. Here, we use noble gases as tracers for deep volatile cycling. Specifically, we construct and apply a kinetic model to estimate the effect of subduction zone metamorphism on the elemental composition of noble gases in amphibole a common constituent of altered oceanic crust. We show that progressive dehydration of the slab leads to the extraction of noble gases, linking noble gas recycling to H2O. Noble gases are strongly fractionated within hot subduction zones, whereas minimal fractionation occurs along colder subduction geotherms. In the context of our modelling, this implies that the mantle heavy noble gas inventory is dominated by the injection of noble gases through cold subduction zones. For cold subduction zones, we estimate a present-day bulk recycling efficiency, past the depth of amphibole breakdown, of 5-35% and 60-80% for 36Ar and H2O bound within oceanic crust, respectively. Given that hotter subduction dominates over geologic history, this result highlights the importance of cooler subduction zones in regassing the mantle and in affecting the modern volatile budget of Earth's interior. (C) 2017 Elsevier B.V. All rights reserved.

Diamond possesses extraordinary material properties, a result that has given rise to a broad range of scientific and technological applications. This study reports the successful production of high-quality single-crystal diamond with microwave plasma chemical vapor deposition (MPCVD) techniques. The diamond single crystals have smooth, transparent surfaces and other characteristics identical to that of high-pressure, high-temperature synthetic diamond. In addition, the crystals can be produced at growth rates from 50 to 150 mum/h, which is up to 2 orders of magnitude higher than standard processes for making polycrystalline MPCVD diamond. This high-quality single-crystal MPCVD diamond may find numerous applications in electronic devices as high-strength windows and in a new generation of high-pressure instruments requiring large single-crystal anvils.

Two experiments were conducted compressing Ta, Re, Pt, and an Fe-Si alloy to ultrahigh pressures using single-crystal chemical vapor deposition (CVD) and natural diamonds. In situ energy-dispersive and angle-dispersive x-ray diffraction were used to determine pressure from known equations of state. We demonstrate that CVD diamonds can be used in diamond anvil cells to reach pressures of nearly 200 GPa. (C) 2003 American Institute of Physics.

Gem-sized single crystals of diamond have been produced by very high growth rate microwave plasma chemical vapor deposition (CVD) and found to exhibit remarkable mechanical properties. The as-grown material has extremely high fracture toughness, and treatment by high-pressure/high-temperature annealing produces crystals that have exceptionally high intrinsic hardness. The annealing appears to induce a novel work hardening of CVD single-crystal diamond. (C) 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

A 820 micron thick single crystal diamond layer epitaxially grown on a single crystal diamond seed (high pressure, high temperature grown synthetic) by microwave plasma chemical vapor deposition with added nitrogen is characterized by an array of analytical techniques before and after annealing the material at high pressures and temperatures. The most striking result is the conversion of the initially dark colored, highly absorbing CVD layer to clear, transparent material after a 1 hour anneal at 7 GPa and 2200 degreesC. IR absorption in the region of the CH stretching modes, 2800 to 3107 cm(-1) shows a remarkable sharpening and persistence of the observed modes. IR absorption in the one-phonon region also indicates the presence of significant concentrations of ionized single substitutional nitrogen in the as grown material. EPR indicates a concentration of neutral single substitutional nitrogen at lattice sites of ca. I ppm, and this changes by less then 30% when annealed at temperatures up to 2200 degreesC. EPR also detects 0.1 ppm of the negatively charged nitrogen-vacancy-hydrogen complex in the as grown diamond, but this anneals out by 1900 degreesC, the negatively charged nitrogen-vacancy complex is below the EPR detection limit in these samples of about 0.1 ppm. Photoluminescence detects the presence of neutral and negatively charged nitrogen-vacancy complexes in the as grown material, and the formation of new, unassigned bands principally in the 800 to 900 nm region. The total detected nitrogen concentration in the sample is ca. 1.5 ppm. (C) 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.