Research articles

The setting in which Earth’s first continental crust formed is unclear because few rocks survive from that time. Geochemical analysis of 4.03-billion-year-old rocks discovered in the Acasta Gneiss Complex, Canada, reveals rocks that are strikingly similar to those formed in Iceland today, implying Earth’s first continental crust was generated in an Iceland-like setting.

The bed topography beneath the Greenland ice sheet controls the flow of ice and its discharge into the ocean. A combination of sparse radar soundings of ice thickness and high-resolution ice motion data suggest that many submarine ice-covered valleys extend significantly deeper below sea level and farther inland than thought.

Bioavailable iron is released from anoxic sediments, such as those that underlie the Peruvian upwelling zone. Analyses of iron levels in sediments from this region suggest that iron release occurs in a relatively narrow range of redox conditions, and that the amount of iron released to the upwelling waters has varied over the past 140,000 years.

The Changbaishan volcanic complex in China cannot be easily explained as the consequence of a mantle plume. Seismic images from the region identify buoyant mantle material that may have been entrained and dragged downwards by the subducting Pacific Plate, but is now escaping upwards through a gap in the plate and producing the intraplate volcanism.

River water circulates through river bed and bank sediments. Model simulations suggest that practically all of the river water that reaches the mouth of the Mississippi River network has circulated laterally through its banks.

The blowout of the Macondo oil well in the Gulf of Mexico in April 2010 injected up to 500,000 tonnes of natural gas, mainly methane, into the deep sea. Spatially extensive measurements of methane dynamics in the months following the spill reveal a rapid rise and fall in the microbial consumption of methane.

The observed depletion of the stratospheric ozone layer from the 1980s onwards is attributed to halogens released through human activities. Model simulations show that stratospheric ozone loss has declined by over 10% since stratospheric halogen loading peaked in the late 1990s, indicating that the recovery of the ozone layer is well under way.

During the last glacial termination, climate changes associated with the Bølling–Allerød warming were seen throughout much of the Northern Hemisphere. A combination of ice-core records and box modelling shows that this climate change was nearly synchronous across high and temperate latitudes.

During volcanic eruptions, solidifying magma ascends through the volcanic conduit, often accompanied by repetitive, drum-beat seismicity. Laboratory experiments on magma samples from Soufrière Hills Volcano, Montserrat, and Mount St Helens Volcano, USA, show that viscous melt formed at the surface between the rising magma and conduit walls can temporarily halt magma ascent, accentuating the cyclical seismicity.

An active core dynamo may have operated on the early Moon. Extraction of palaeomagnetic pole positions on the Moon from magnetic anomalies measured by the Lunar Prospector and Kaguya orbiters suggests that the ancient lunar dynamo experienced reversals and an ancient reorientation of the Moon rotated the geographic locations of the poles.

The explosive style of volcanic eruptions has been linked to gas separation from magmas in the shallow crust. Geochemical analysis of magmas erupted over the past 600 years at Kīlauea Volcano, Hawai‘i, now reveal a link between eruption style and the geochemistry of magmas formed at greater depths, implying that some magmas are predisposed towards explosivity.

Ethanol-based vehicles are thought to generate less pollution than gasoline-based vehicles. An analysis of pollutant concentrations in the subtropical megacity of São Paulo, Brazil, reveals that levels of ozone pollution fell, but levels of nitric oxide and carbon monoxide rose, during periods of prevailing gasoline use relative to ethanol use.

Extreme heatwave events are expected to become increasingly common as a consequence of climate change. Analyses of the 2003 and 2010 mega-heatwaves in Europe suggest that atmospheric boundary-layer dynamics and feedbacks with the drying land surface lead to the build-up of heat in the atmosphere and extremely hot temperatures.

The balance between carbonate subduction into the deep Earth and CO₂ release through degassing at volcanoes is critical for the carbon cycle. Geochemical analyses of an exhumed subduction zone complex in Greece show that fluid-mediated reactions could liberate significant amounts of carbon from the subducting slab for later release at arc volcanoes.

Dams have starved the lower Mississippi River of sediment over recent decades, suggesting that the drowning of the delta is inevitable. Analysis of the rivers suspended sediment load and morphodynamic modelling suggest that the amount of sand essential for land building has not significantly decreased since dam construction, with sand remaining available for several centuries.

The martian atmosphere has progressively thinned, allowing increasingly smaller meteorites to survive unscathed and impact the surface. The distribution of small craters in ancient river deposits on Mars suggests an atmospheric pressure less than that needed to warm the martian surface above freezing 3.5 billion years ago, when rivers presumably flowed.

Globally increased temperatures and a perturbation of the carbon cycle and biosphere characterized the Palaeocene–Eocene Thermal Maximum about 55.9 million years ago, but its effect on ocean productivity is controversial. Records of marine barite accumulation rates suggest that carbon sequestration during the event could have been enhanced by an efficient biological pump.

The downward transport of stratospheric air can deliver significant quantities of ozone to the upper troposphere. An analysis of satellite data suggests that year-to-year variations in stratospheric circulation can account for around half of the interannual variability in tropospheric ozone levels in the northern mid-latitudes.

During the expansion of the Antarctic ice sheet about 14 million years ago, sea surface temperatures in the Southern Ocean rose. Climate model simulations suggest that this short-lived warming was related to changes in ocean–atmosphere circulation induced by the growth of the ice sheet.

Lavas erupted at ocean island hotspots have complex geochemical signatures. Numerical simulations suggest that this complexity may result from the mixing of subducted oceanic crust with reservoirs of more primitive material in the deep mantle, with the resulting mixture entrained into rising mantle plumes.