Volume 6 Issue 7, July 2013

China's carbon dioxide emissions are rising fast. Yet, per capita, gross domestic product and energy use are only a fraction of their United States equivalents. With a growing urban middle class, the trend will continue, but there is progress on the path to a low-carbon economy.

Planetary protection policies aim to guard Solar System bodies from biological contamination from spacecraft. Costly efforts to sterilize Mars spacecraft need to be re-evaluated, as they are unnecessarily inhibiting a more ambitious agenda to search for extant life on Mars.

The way in which seismic waves pass through the core suggests alignment of iron crystals within the solid inner core. Experiments indicate that iron at inner-core conditions may be weaker than thought and easily allow deformation of iron crystals.

The daily vertical migration of small marine animals transfers organic carbon from the surface ocean to depth. An assessment of acoustic data reveals that the depth of migration is closely tied to subsurface oxygen levels throughout much of the global ocean.

Mantle flow patterns may be reconstructed from mineral orientations. Experiments show that the high-pressure mineral post-perovskite can inherit texture from its lower-pressure counterpart, suggesting new ways of interpreting flow in the deepest mantle.

Atmospheric aerosols affect climate by scattering and absorbing sunlight and by modifying clouds. Model simulations suggest that anthropogenic aerosols suppressed tropical storm activity over the Atlantic throughout much of the twentieth century.

About 4 billion years ago, the terrestrial planets were bombarded by asteroids following an orbital shake-up of the outer Solar System. Lunar samples, planetary cratering records and dynamical models piece together an increasingly coherent view of this bombardment interval.

Great White Spot—a rare planet-encircling storm—raged on Saturn in 2010–2011. Analyses of high-resolution spacecraft imagery and numerical modelling reveal a dynamic storm head powered by sustained convection in the zonal flow of Saturn’s atmosphere.

Temperate and tropical rivers serve as a substantial source of carbon dioxide to the atmosphere. Organic matter measurements in the Amazon River suggest that terrestrial macromolecules contribute significantly to this outgassing.

The frequency of North Atlantic tropical storms varies markedly on decadal timescales. An analysis of climate model simulations suggests that anthropogenic aerosols lowered the frequency of tropical storms in the North Atlantic over the twentieth century.

The development and termination of El Niño events seem to be coupled with the seasonal cycle. Statistical analyses suggest that this link reflects the presence of a combination climate mode with periods of 10 and 15 months.

Throughout the ocean, countless small animals swim to depth in the daytime, presumably to seek refuge from large predators. An analysis of backscatter data from acoustic Doppler profilers suggests that migration intensifies oxygen depletion in the upper margin of oxygen minimum zones.

Altimeter data suggest that sea level rose by about 2.4 mm per year from 2005 to 2011, but estimates of the relative contributions of ocean warming and increased ocean mass are equivocal. An analysis of ocean temperature and satellite gravity data suggests that the delivery of meltwater from ice sheets and mountain glaciers contributed 75% of the observed sea-level rise.

Coral records from the Barbados have been used to infer that, due to ice expansion, sea level was 120 m lower than today during the Last Glacial Maximum. A 3D simulation of the mantle in this region suggests these estimates were biased by the presence of a subducted slab, and indicates the sea-level difference was closer to 130 m.

Greenhouse warmth during the Cretaceous period was interrupted by several intervals of cooling. Marine sediment analyses and biogeochemical modelling suggest that a decline in the abundance of planktonic foraminifera and nannoconids 116–114 million years ago was linked to sea surface cooling.

How noble gases are recycled from the atmosphere back into the mantle has been unclear. High-pressure experiments demonstrate that noble gases are highly soluble in an important hydrous mineral in altered oceanic crust, suggesting that subduction of this type of crust may be a significant pathway for noble gas flux back into the mantle.

Stable fault slip, or creep, is thought to occur in unconsolidated sediments that form shallow parts of continental strike-slip faults. Numerical simulations show that creep events observed on faults in California also require the presence of a shallow, unstable layer of rock, the thickness of which influences the duration of the creep event.

The observed seismic anisotropy in the Earth’s inner core has been explained by the preferential alignment of grains by plastic deformation. Measurements of the strength of iron at core pressures suggest that the inner core is weaker than previously thought and deforms by dislocation creep.

Flow in the deep mantle is thought to create textures in the high-pressure mineral post-perovskite. Laboratory simulations of the transformation between lower-pressure perovskite and post-perovskite show that post-perovskite can also inherit textures from the perovskite phase, and vice versa.

The marine nitrogen cycle was altered during the transition from glacial to interglacial conditions. An analysis of δ¹⁵N records throughout the world’s oceans suggests that rates of denitrification in the water column accelerated during the last deglaciation.

Long after the planets of the Solar System formed, catastrophic collisions continued, with a climax about 4 billion years ago during an interval called the Late Heavy Bombardment. The scars of this geologic violence are evident today in the ancient cratered terrains of planetary surfaces. The interval of bombardment is thought to have shaped the terrestrial planets and moons, their atmospheres and possibly even the onset of life. In this web focus, we present research papers, overview articles and opinion pieces that discuss how large impacts influenced the evolution of the early Solar System.