Reviews & Analysis

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.

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.

A substantial amount of atmospheric carbon taken up on land is transported laterally from upland terrestrial ecosystems to the ocean. A synthesis of the available literature suggests that human activities have significantly increased soil carbon inputs to inland waters, but have only slightly affected carbon delivery to the open ocean.

Different measurements of inner core rotation have delivered inconsistent results. An analysis of seismic data provides a resolution of this discrepancy by suggesting decadal variations in inner core rotation rate.

The amount of carbon stored in the deep ocean varied over glacial–interglacial cycles. Southern Ocean sediments from the past 360,000 years show that carbon storage also fluctuated within glacial periods, in concert with the fertilization of the Southern Ocean by wind-borne dust.

High-temperature water–rock reactions produce large quantities of hydrogen, which must be transported to cooler settings to sustain life. Lower-temperature hydrogen generation could potentially support life in situ and free subsurface microbes from photosynthetic constraints.

Patches of deposits containing unusual mafic minerals are observed in and around some large lunar impact craters. Numerical simulations suggest that in the slowest of these impacts, asteroidal material, alien to the Moon, could have survived.

A 500,000-year-long period of warmth in the middle Eocene was marked by high atmospheric carbon dioxide concentrations and prolonged dissolution of carbonate in the deep oceans. Numerical simulations attempting to capture these features identify gaps in our understanding of the causes of this and similar perturbations.

Sinking slabs of oceanic lithosphere often stagnate in Earth's mantle. Experiments show that common slab minerals transform to their high-pressure, high-density counterparts at very slow rates, thus keeping the slabs buoyant and impeding subduction.

Volcanic rocks erupted at mid-ocean ridges can record the temperature of the underlying mantle. Ancient crust in the Atlantic Ocean formed from anomalously hot mantle, possibly warmed by continental insulation before the opening of the ocean basin.

Antarctic climate has undergone substantial shifts in past decades, but whether these changes are unusual in the long term is unclear. Ice-core records suggest that some aspects of this variability are unique to the past two millennia.

Rainfall disparities are expected to intensify in response to anthropogenic climate change. Model simulations suggest that wet regions and seasons will get wetter, and that a warmer equator will get wetter too.

Temperature change over the past 2,000 years has shown pronounced regional variability. An assessment of all available continental temperature reconstructions shows a clear twentieth century warming trend, but no evidence of a coherent Little Ice Age or Medieval Warm Period.

Snow and ice influence the climate and chemistry of the polar atmosphere. Field experiments in Alaska point to the significance of surface snow for polar ozone depletion events.

Photosynthetic microbes, collectively termed phytoplankton, are responsible for the vast majority of primary production in marine waters. A synthesis of the latest research suggests that two broad nutrient limitation regimes — characterized by nitrogen and iron limitation, respectively — dictate phytoplankton abundance and activity in the global ocean.

The sea floor around mid-ocean ridges is often carpeted by hummocky lava flows. Images from the Southwest Indian Ridge sea floor, however, show a smooth texture created by exhumation and widespread exposure of altered mantle rocks.

Gold is often deposited in Earth's crust by fluids that percolate through rock fractures. Earthquakes cause rock fractures to expand rapidly and could cause the fluids to evaporate, triggering almost instantaneous gold deposition.

Scarce food supplies could hinder biological activity in the ocean's depths. However, measurements at Mariana Trench point to an unexpectedly active microbial community in the deepest seafloor setting on the planet.