Research articles

The pressures and temperatures experienced by material flung from craters following impact events are expected to preclude survival of organics. The preservation of biomarkers in impact glass from the Darwin crater in Tasmania suggests that organic matter can survive in the distal products of meteorite impact.

The causal connection between human activities and the evolution of climate warming over the past century is not fully understood. A state-of-the-art statistical analysis of time series of temperature and radiative forcing reveals that reductions in ozone-depleting substances and methane have contributed to the slow-down in warming since the late 1990s.

The flow of ductile rocks in the deep crust and uppermost mantle is thought to add stress to faults in the shallow crust, potentially bringing the faults closer to rupture. Measurements of fault offsets in the Italian Apennines show that earthquake recurrence is largely controlled by viscous flow of deeper rocks in localized zones.

The boundary between Earth’s rigid lithosphere and ductile asthenosphere is marked by a seismic discontinuity. Laboratory experiments on basaltic magmas show that melts should pond at pressures that correspond to the lithosphere–asthenosphere boundary. Thus, magma ponding could explain the observed seismic discontinuity.

The predictability of heat waves in the mid-latitudes has been limited to the 10-day range of weather forecasts. An integration of a climate model that spans 12,000 years reveals a pattern in atmospheric planetary waves that tends to precede heat waves in the US, extending potential predictability to 20 days.

Modern grasslands are dominated by grasses that use the C₄ photosynthetic pathway, and were established about 8 million years ago. A sediment record suggests that in southwestern Africa, the expansion of grasslands was associated with increasing aridity and fire activity, both of which favour grasses that use the C₄ pathway.

Glacial Termination II was marked by a rise in atmospheric CO₂ concentrations and global temperature. An analysis of air bubbles from an Antarctic ice core suggests that during the first phase of deglaciation, Antarctic temperature and atmospheric CO₂ concentrations increased together, whereas CO₂ lagged behind temperature rise during the second phase.

In the tropics, substantially more rain falls just north of the Equator. An analysis of satellite observations, reanalysis data and model simulations suggests that the meridional ocean overturning circulation contributes significantly to the tropical rainfall peak north of the Equator.

The position of the intertropical convergence zone is thought to be linked to changes in the Earth’s climate state. Analyses of marine sediment show that over the past 25,000 years, the intertropical convergence zone over the Atlantic Ocean migrated in response to climate changes.

The recent rise in surface air temperatures over southern Africa is thought to largely result from the increase in atmospheric greenhouse gas concentrations. An analysis of climate data from the past four decades suggests that the warming may be linked to changes in Southern Hemisphere circulation induced by Antarctic ozone loss.

Subglacial meltwater channels beneath the Antarctic Ice Sheet have been reported, but the nature and distribution of these meltwater pathways are unclear. Remote sensing observations reveal persistent channelized features beneath the Filchner–Ronne Ice Shelf in West Antarctica, suggesting widespread channelized flow driven by melting.

The differentiation of the Earth into mantle and core implies that there is a mechanism to separate iron from silicates. Three-dimensional imaging of samples experimentally subjected to high pressures reveals that liquid iron forms interconnected melt networks at lower mantle conditions, suggesting pathways through which iron can percolate towards the core.

The end of the African Humid Period about 6,000 years ago was associated with vegetation change and decreased precipitation. Conceptual modelling suggests that the nature of the feedback between climate and vegetation is dependent on vegetation type and diversity.

Field measurements have revealed much higher concentrations of hydroxyl radicals than expected in regions with high loads of the biogenic volatile organic compound isoprene. Results from isoprene oxidation experiments suggest that the additional recycling of radicals in the presence of isoprene contributes to hydroxyl radical enhancement in these regions.

Spectral observations from the Mars Express spacecraft have revealed an ozone layer that forms at night in south polar Mars. Data analysis and climate models suggest that poleward transport of oxygen and seasonal changes in hydrogen radicals explain the ozone layer’s presence in the southern hemisphere, and its absence in the north.

Some mantle plumes are enriched in ³He, but the source of this primordial isotope is unclear. The partitioning behaviour of helium between silicate and iron melts—as determined by experiments—suggests that sufficient helium may have been incorporated into the core when the Earth differentiated to explain the anomalous leakage at the Earth’s surface.

Little is known about the structure of possible mantle materials of extra-solar super-Earths with interior pressures of up to 1,000 GPa. Dynamic X-ray diffraction measurements of ramp-compressed magnesium oxide, an important component of Earth’s mantle, show a solid–solid state transition at about 600 GPa, with a high-pressure structure that is stable up to 900 GPa.

The surface expressions of mantle plumes—known as hotspot tracks—are rarely observed on continents because the lithosphere is so thick. Analysis of seismic data from the eastern United States, combined with geodynamical modelling, reveals a linear, east–west-trending seismic anomaly that may represent a hidden hotspot track extending from Missouri to Virginia.

Comets harbour the organic precursors of amino acids. High-velocity impact experiments into icy targets suggest that impacts involving icy planetary bodies could be a viable pathway to synthesize the complex organic compounds needed for life.

The long-term stability of the continents has been attributed to a trade-off between thermal and compositional effects. Numerical simulations of the evolution of continents over 3 billion years, however, show that this state is ephemeral, and continents that are neutrally buoyant today were more (or less) buoyant in the geologic past.