Deep continental roots and cratons.

The formation and preservation of cratons-the oldest parts of the continents, comprising over 60 per cent of the continental landmass-remains an enduring problem. Key to craton development is how and when the thick strong mantle roots that underlie these regions formed and evolved. Peridotite melting residues forming cratonic lithospheric roots mostly originated via relatively low-pressure melting and were subsequently transported to greater depth by thickening produced by lateral accretion and compression. The longest-lived cratons were assembled during Mesoarchean and Palaeoproterozoic times, creating the stable mantle roots 150 to 250 kilometres thick that are critical to preserving Earth's early continents and central to defining the cratons, although we extend the definition of cratons to include extensive regions of long-stable Mesoproterozoic crust also underpinned by thick lithospheric roots. The production of widespread thick and strong lithosphere via the process of orogenic thickening, possibly in several cycles, was fundamental to the eventual emergence of extensive continental landmasses-the cratons.

Size Isn't Everything: Geometric Tuning in Polycyclic Aromatic Hydrocarbons and Its Implications for Carbon Nanodots.

Recent developments in light-emitting carbon nanodots and molecular organic semiconductors have seen renewed interest in the properties of polycyclic aromatic hydrocarbons (PAHs) as a family. The networks of delocalized π electrons in sp2-hybridized carbon grant PAHs light-emissive properties right across the visible spectrum. However, the mechanistic understanding of their emission energy has been limited due to the ground state-focused methods of determination. This computational chemistry work, therefore, seeks to validate existing rules and elucidate new features and characteristics of PAHs that influence their emissions. Predictions based on (time-dependent) density functional theory account for the full 3-dimensional electronic structure of ground and excited states and reveal that twisting and near-degeneracies strongly influence emission spectra and may therefore be used to tune the color of PAHs and, hence, carbon nanodots. We particularly note that the influence of twisting goes beyond torsional destabilization of the ground-state and geometric relaxation of the excited state, with a third contribution associated with the electric transition dipole. Symmetries and peri-condensation may also have an effect, but this could not be statistically confirmed. In pursuing this goal, we demonstrate that with minimal changes to molecular size, the entire visible spectrum may be spanned by geometric modification alone; we have also provided a first estimate of emission energy for 35 molecules currently lacking published emission spectra as well as clear guidelines for when more sophisticated computational techniques are required to predict the properties of PAHs accurately.

Dynamic earthquake rupture preserved in a creeping serpentinite shear zone.

Laboratory experiments on serpentinite suggest that extreme dynamic weakening at earthquake slip rates is accompanied by amorphisation, dehydration and possible melting. However, hypotheses arising from experiments remain untested in nature, because earthquake ruptures have not previously been recognised in serpentinite shear zones. Here we document the progressive formation of high-temperature reaction products that formed by coseismic amorphisation and dehydration in a plate boundary-scale serpentinite shear zone. The highest-temperature products are aggregates of nanocrystalline olivine and enstatite, indicating minimum peak coseismic temperatures of ca. 925 ± 60 °C. Modelling suggests that frictional heating during earthquakes of magnitude 2.7-4 can satisfy the petrological constraints on the coseismic temperature profile, assuming that coseismic fluid storage capacity and permeability are increased by the development of reaction-enhanced porosity. Our results indicate that earthquake ruptures can propagate through serpentinite shear zones, and that the signatures of transient frictional heating can be preserved in the fault rock record.

Earliest Pottery on New Guinea Mainland Reveals Austronesian Influences in Highland Environments 3000 Years Ago.

Austronesian speaking peoples left Southeast Asia and entered the Western Pacific c.4000-3000 years ago, continuing on to colonise Remote Oceania for the first time, where they became the ancestral populations of Polynesians. Understanding the impact of these peoples on the mainland of New Guinea before they entered Remote Oceania has eluded archaeologists. New research from the archaeological site of Wañelek in the New Guinea Highlands has broken this silence. Petrographic and geochemical data from pottery and new radiocarbon dating demonstrates that Austronesian influences penetrated into the highland interior by 3000 years ago. One potsherd was manufactured along the northeast coast of New Guinea, whereas others were manufactured from inland materials. These findings represent the oldest securely dated pottery from an archaeological context on the island of New Guinea. Additionally, the pottery comes from the interior, suggesting the movements of people and technological practices, as well as objects at this time. The antiquity of the Wañelek pottery is coincident with the expansion of Lapita pottery in the Western Pacific. Such occupation also occurs at the same time that changes have been identified in subsistence strategies in the archaeological record at Kuk Swamp suggesting a possible link between the two.

Clinical inquiries: what is the most effective way to relieve symptoms of acute stress disorder?

Cognitive Behavioral Therapy (CBT) that emphasizes exposure-based treatment is the most effective intervention for adults with acute stress disorder (ASD). Exposure-based therapy reduces symptoms in adults with ASD more than CBT that focuses on cognitive restructuring; both therapies are better than no treatment at all. Avoid drug treatment within 4 weeks of appearance of symptoms, unless distress is too severe to be managed with psychological treatment alone.