Volume 6 Issue 11, November 2013

Access to metals and minerals is restricted mostly by geopolitical constraints, and not by a shortage of mineable deposits. In the face of rising demand, a full inventory of these commodities — in the Earth's crust as well as in recyclable waste — is urgently required.

Renewable energy requires infrastructures built with metals whose extraction requires more and more energy. More mining is unavoidable, but increased recycling, substitution and careful design of new high-tech devices will help meet the growing demand.

Mineable phosphorus reserves are confined to a handful of countries. Reductions in wastage could free up this resource for low-income, food-deficient countries.

Understanding the processes that govern the complex spatial structure of rainfall is crucial. Idealized numerical simulations reveal the strong influence that ocean heat transport exerts on this structure.

Episodes of excessive magmatism have repeatedly formed large volcanic provinces on Earth. Seismic data from the Shatsky Rise in the northwestern Pacific Ocean reveal that such oceanic plateaux can be built from individual, giant volcanoes.

About 5,500 years ago, there was a shift from savannah to desert vegetation in the Sahara. Conceptual modelling suggests that the transition was controlled by a climate–vegetation feedback that was also influenced by plant diversity.

Some giant ore deposits are formed from magma, but the precise controls on their formation are unclear. A Perspective article analyses the distribution of some diamond, platinum-group element and gold deposits worldwide, and suggests that the structure and composition of sub-continental lithospheric mantle could play a role in ore genesis.

Giant ore deposits are priority targets for mining companies. A review of the characteristics of several giant porphyry and epithermal deposits worldwide suggests that they formed from ordinary processes that were fortuitously operating at maximum efficiency.

Porphyry ore deposits supply much of the copper, molybdenum, gold and silver used by humans. A review of the main processes that trigger porphyry ore formation suggests that sulphide saturation of the magmas that supply the metals could be the overriding mechanism that helps control the temporal and spatial distribution of the ore deposits.

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.

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.

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.

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.

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.

Palaeoclimate records indicate lower El Niño/Southern Oscillation (ENSO) variance during the middle Holocene compared with today, but the mechanisms leading to this muted variability are not clear. A 175-year oxygen isotope record from a Porites coral microatoll in the NINO3.4 region records persistently reduced ENSO variance about 4,300 years ago, and season-specific analyses of the record suggest that insolation played an important role in this change.

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.

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 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.

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.

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 structure of oceanic plateaux is unclear, as they are remote and submerged beneath the seas. Seismic images of the Tamu Massif, part of the Shatsky Rise oceanic plateau in the northwestern Pacific Ocean, show that it is a single immense volcano, potentially the largest on Earth.

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.

The demand for metals and other natural resources is surging and, in some instances, demand has already outstripped supply. Discovery of new deposits or the exploitation of known lower-grade ore deposits could offer solutions, but their implementation is not always straightforward, given political constraints and the complexities of international trade. This focus issue brings together a collection of review articles and opinion pieces that highlight the emerging science of the processes responsible for the formation of economic-grade ore deposits, and discuss the societal conditions and implications of their exploitation.