Reviews & Analysis

The Earth's mantle constitutes over 80% of the planet's volume and is a key reservoir in global geochemical cycling. An overview of the progress in understanding the generation of mid-ocean-ridge basalt from mantle melt shows that a variety of processes chemically alter mantle signals in the melt generated at depth before its eruption at the sea floor.

Most of the dust in Antarctic ice cores originates in the glacial outwash of Patagonia. Sedimentary evidence suggests that during the last glacial period, pro-glacial lakes provided an on/off switch for the dust flux to Antarctica.

The timing of the earliest production of oxygen by photosynthesis is hotly debated. Haematite crystals from Pilbara, Australia, may provide evidence for a deep ocean that was at least occasionally oxygenated by photosynthetic microbes 3.46 billion years ago.

The enhanced Arctic warming over the past three decades is attracting much attention. Combining forward and inverse models with observations suggests that regional changes in aerosol concentrations have contributed significantly.

Volcanic rocks at island arcs can show characteristics of the subducting oceanic plate. The isotopic signature of rocks at the Izu-Bonin arc in the northwest Pacific suggest the presence of Indian-type rather than Pacific-type oceanic crust.

The vast Thaumasia plateau on Mars is fringed by extensive zones of deformation. Topographic and structural analysis suggests that the plateau may have slipped in a massive landslide, deforming its margins in the process.

Cordilleran orogenic systems are long belts of deformation and magmatism that form when oceanic plates subduct beneath continental ones. Links between processes in the upper continental plate explain key features of Cordilleran systems, such as cyclical trends in the flux and composition of magma supplied to the upper plate.

NASA's Opportunity rover found enigmatic sulphate deposits at Meridiani Planum on Mars. A proposal that the deposits are sublimation leftovers of large ice-fields, similar in scale to those at the present-day polar caps, adds to the existing hypotheses.

Aerosols in the atmosphere alter the radiative balance of the Earth by reflecting or absorbing solar radiation. Space-borne measurements of clouds and aerosols advected over the southeastern Atlantic Ocean indicate that the greater the cloud cover below the aerosols, the more likely the aerosols are to heat the planet.

Surface water is known to shape the formation and growth of valleys and channels. However, in some geologic settings, groundwater seeping upwards is important for the development of channel networks.

Nutrient-rich tropical and agricultural soils release vast quantities of the highly potent greenhouse gas nitrous oxide. New measurements show that vegetation-free patches of tundra in subarctic Europe can also emit large quantities of this gas.

According to one controversial idea, increases in atmospheric greenhouse-gas concentrations due to human activities can be detected as early as several thousand years ago. Eight years after the publication of this hypothesis, controversy continues.

Marine dissolved oragnic matter contains roughly as much organic carbon as all living biota on land and in the oceans combined. New techniques in analytical chemistry show that a significant portion of this material has undergone thermal alteration, either on land or in sediments deep below the sea floor.

Ice ages in the North Pacific Ocean and the Southern Ocean were marked by low productivity. Accumulating evidence indicates that strong stratification restricted the supply of nutrients from the deep ocean to the algae of the sunlit surface in these regions.