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The timing of onset of modern-style plate tectonics on Earth is debated. Analysis of rocks in the West African metamorphic province, which is more than 2 Gyr old, reveals that some minerals formed under conditions similar to those in modern-day subduction zones, suggesting that subduction occurred on the Palaeoproterozoic Earth.
Subduction modifies the cycling of Earth’s volatile elements. Geochemical analyses of fragments of mantle rocks collected above the Batan Island subduction zone, Philippines, suggest that wet sediment melts are released from the subducted slab, followed later by release of aqueous fluids, yet a significant amount of water is retained in the wedge.
Peatlands store vast amounts of organic carbon, owing to anoxic conditions, which prevent decay. Laboratory and field experiments suggest that drought-induced increases in oxygen stimulate microbial growth and the breakdown of peatland carbon.
Atmospheric carbon dioxide levels rose at the end of the last glacial period, but the sources of this carbon are uncertain. Ice-core data and carbon-cycle modelling suggest that the disappearance of a terrestrial inert carbon pool may have contributed to the rise.
Atmospheric aerosols can both suppress and foster the development of clouds and precipitation, depending on meteorological conditions. Ten years of observations, together with model simulations, suggest that aerosols stimulate the vertical development of warm-base mixed-phase clouds.
The role of the North American seaway in creating and maintaining Late Cretaceous global greenhouse conditions has been unclear. An isotopic analysis of marine turtle and fish fossils from western Kansas and the Mississippi embayment reveals that the inflow of Tethyan surface waters to the seaway was limited.
The electric discharge of a thundercloud in the troposphere is often accompanied by upper-atmospheric electric discharges such as sprites or halos. Numerical simulations of the electric response of the mesosphere to lightning suggest that the process of electron associative detachment is fundamental to upper-atmospheric electrodynamics.
Massive-turbidite deposits are common in deep-water environments. Numerical simulations suggest that when turbulence is extinguished as turbidity currents reach areas of minimal slope, sediment reworking ceases, which allows the deposition of massive units.
A series of extreme cooling episodes, starting 750 million years ago, could have repeatedly turned the planet into an ice-covered snowball. Carbon cycle modelling suggests that the timing of the glaciations can be explained by chemical weathering rates.
Gas hydrates have been suggested as a carbon source for Palaeogene hyperthermal events, but warm seafloor temperatures are thought to have limited their accumulation. Numerical simulations suggest that enhanced organic carbon sedimentation and methanogenesis could have compensated for the smaller area of hydrate stability.
The Neoproterozoic Snowball Earth glaciations were separated by tens of millions of years, although models suggest glacial inception should occur within millions. Numerical modelling suggests that the delay could be explained by inherent limits on silicate weathering rates controlled by the availability of fresh rock.
The origin of the Bushveld Complex, South Africa, is elusive. Identification and dating of a radial swarm of volcanic dykes suggests that a mantle plume affected the region, but was active 600 million years before the Bushveld Complex formed, implying that the Bushveld magmas could be an indirect consequence of the plume.
