Search for Evolutionary Changes in the Periods of Cepheids: BY Cas

Astronomy Letters - For the low-amplitude Cepheid BY Cas we have constructed an O ? C diagram spanning a time interval 123 years. The O ? C diagram has the shape of a parabola, which...     

A gradual transition to plate tectonics on Earth between 3.2 to 2.7 billion years ago

Zircon crystals precipitated from granitoid magmas contain a robust record of the age and chemistry of continental magmatism spanning some 4.375 Ga of Earth history, a record that charts initiation of plate tectonics. However, constraining when exactly plate tectonics began to dominate crustal growth processes is challenging as the geochemical signatures of individual rocks may reflect local subduction processes rather than global plate tectonics. Here we apply counting statistics to a global database of coupled U–Pb and Hf isotope analyses on magmatic zircon grains from continental igneous and sedimentary rocks to quantify changes in the compositions of their source rocks. The analysis reveals a globally significant change in the sources of granitoid magmas between 3.2 and 2.7 Ga. These secular changes in zircon chemistry are driven by a coupling of the deep (depleted mantle) and shallow (crustal) Earth reservoirs, consistent with a geodynamic regime dominated by Wilson cycle style plate tectonics.     

Correspondence analysis applied to volcanic aerosols

A statistical analysis of volcanic aerosol based on 1,083 variables including concentration, grain-size and site variabilities establishes correlations between sites and among chemical elements.Variation curves of element concentration show parallel behaviour. High coefficients of correlation between anions and cations confirm associations between elements.     

New data on the Albian-Cenomanian radiolarians from the Karai Formation (South India)

Radiolarians from the lower part of the Karai Formation (upper Albian-middle Cenomanian) are studied in detail for the first time. Among over 50 radiolarian species identified in the formation, there are Acaeniotyle amplissima (Foreman), Savaryella novalensis (Squinabol), S. quadra (Foreman), Vitorfus campbelli Pessagno, Archaeodictyomitra montisserei (Squinabol), Holocryptocanium barbui Dumitrica, Pseudoeucyrtis sp. cf. Ps. spinosa (Squinabol), Stichomitra communis Squinabol, Tubilustrionella transmontanum (O’Dogherty), and others. The discovered radiolarians are divided into the Halesium triacanthum-Orbiculiforma nevadaenis (late Albian-early Cenomanian), Crucella latum-Cryptamphorella micropora (late Albian?-early Cenomanian), and Becus sp. B-Godia concava (terminal Albian-middle Cenomanian) assemblages. In general, the Albian-Cenomanian radiolarians of South India are comparatively less diverse than the concurrent assemblages of the Mediterranean region and California. In taxonomic composition and morphological peculiarities, they are comparable with the Aptian-Albian radiolarians of Western Australia (Ellis, 1993). Consequently it can be postulated that sea basins of South India were situated during the Albian-Cenomanian in the temperate latitudes of the Southern Hemisphere.     

Dispersal of arbuscular mycorrhizal fungi and dark septate endophytes by Ctenomys cf. knighti (Rodentia) in the northern Monte Desert of Argentina

In arid and semi-arid environments, root-associated fungi may play a key role in plant communities (e.g., seedling establishment, nutrient acquisition, plant survival and heat tolerance). Several studies have shown the importance of small mammals as consumers and dispersal agents of mycorrhizal fungi spores in tropical and temperate ecosystems. However, little is known about the dispersal of infective propagules of endophytic fungi in arid and semi-arid ecosystems. This study analyzed the potential role of the subterranean rodent Ctenomys cf. knighti as a dispersal agent of root-associated fungi. In order to demonstrate this role, we analyzed: (1) the incidence of colonization of arbuscular mycorrhizae and dark septate endophytes on representative plant species of the Monte Desert; (2) the presence of fungal structures of arbuscular mycorrhizae and dark septate endophytes in C. cf. knighti fecal samples; and (3) the infectivity of the fungal propagules contained in the scat and their growth effects on nine native plant species. Data strongly suggest that this South American subterranean rodent may play a key role as a dispersal agent of arbuscular mycorrhizae and dark septate endophytes fungi in the arid environment of the northern Monte Desert of Argentina.     

Could CoRoT-7b and Kepler-10b be remnants of evaporated gas or ice giants?

We present thermal mass loss calculations over evolutionary time scales for the investigation if the smallest transiting rocky exoplanets CoRoT-7b (∼1.68R_Earth) and Kepler-10b (∼1.416R_Earth) could be remnants of an initially more massive hydrogen-rich gas giant or a hot Neptune-class exoplanet. We apply a thermal mass loss formula which yields results that are comparable to hydrodynamic loss models. Our approach considers the effect of the Roche lobe, realistic heating efficiencies and a radius scaling law derived from observations of hot Jupiters. We study the influence of the mean planetary density on the thermal mass loss by placing hypothetical exoplanets with the characteristics of Jupiter, Saturn, Neptune, and Uranus to the orbital location of CoRoT-7b at 0.017 AU and Kepler-10b at 0.01684 AU and assuming that these planets orbit a K- or G-type host star. Our findings indicate that hydrogen-rich gas giants within the mass domain of Saturn or Jupiter cannot thermally lose such an amount of mass that CoRoT-7b and Kepler-10b would result in a rocky residue. Moreover, our calculations show that the present time mass of both rocky exoplanets can be neither a result of evaporation of a hydrogen envelope of a “Hot Neptune” nor a “Hot Uranus”-class object. Depending on the initial density and mass, these planets most likely were always rocky planets which could lose a thin hydrogen envelope, but not cores of thermally evaporated initially much more massive and larger objects.