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The formation process for the oldest mineral grains on Earth has remained elusive. A comparison of trace element concentrations of these ancient zircons with known material suggests melting of igneous crust as their source.
Anoxic carbon decomposition is thought to depend on the energetics of electron acceptors. Mass spectrometry measurements of floodplain sediments reveal that the energetics of organic compounds can also determine whether they are decomposed.
Groundwater that predates the Holocene is commonly assumed to be unaffected by modern contamination. A global analysis of fossil groundwater suggests that modern contaminants are present in deep wells that tap fossil aquifers.
The timing and number of large impact basins on early Mars are poorly constrained. Gravity and topographic analyses support a lull in basin-forming impacts following the main stage of accretion.
Little is known about the deep carbon cycle during the Archaean. High- pressure and -temperature experiments indicate that the subduction of organic carbon on a hotter, younger Earth was efficient, helping to sequester carbon in Earth’s interior.
Brackish to salty waters have been found in inland areas of delta aquifers. Geophysical data and modelling suggest that salty groundwater in the Red River delta originates from trapped seawater contained in underlying Holocene marine deposits.
River piracy—the diversion of one stream’s headwaters into another—has occurred on long timescales. An analysis of streamflow and digital elevation models documents river re-routing in response to glacier retreat in Yukon, Canada in May 2016.
Greenland’s ice loss depends on propagation of mass loss from the marine glacier termini to the interior. An analysis of surface elevation change in 16 glacier catchments shows that the up-glacier extent of thinning is limited by glacier geometry.
Despite evidence for an ice-rich outer shell, little water ice has been observed on the surface of Ceres. Lobate morphologies observed on Ceres that are increasingly prevalent towards the dwarf planet’s poles are consistent with ice-rich flows.
The late Palaeozoic was characterized by glacial cycles. Numerical simulations suggest that increased silicate weathering due to mountain uplift and soil removal caused atmospheric CO2 to fall below the threshold for glaciation.
Venus lacks plate tectonics, but some trenches on Venus resemble subduction zones. Laboratory experiments suggest that upwelling plumes can initiate localized subduction of a thin lithosphere such as the one on Venus.
Bioavailable glacial carbon has been thought to be largely ancient or anthropogenic. Analyses of carbon dynamics in an Antarctic supraglacial stream reveal that non-photosynthetic production relies on organic carbon from photosynthetic microbes.
Glacial systems are important sources of dissolved organic carbon to downstream ecosystems. Observations of carbon dynamics on the Greenland ice sheet reveal substantial melt season production and export of microbial dissolved organic carbon.
Frictional charging of granular materials may readily occur on Saturn’s moon Titan. Laboratory experiments under Titan-like conditions suggest that the resulting electrostatic forces are strong enough to affect sand transport on Titan.
Most monitoring of methane well leakage focuses on emissions of methane gas to the atmosphere. In a controlled-release field experiment, significant methane also persisted in aquifer groundwater due to lateral migration along bedding planes.
Transient streaks on Martian slopes have been attributed to liquid water. Simulations show that a dry avalanche process involving the flow of gas in the Martian soil due to temperature contrasts can instead explain these recurring features.
The moon Phobos is spiralling inwards towards its disintegration to eventually form a ring around Mars from which new moons may form. Simulations suggest that this is just the latest of multiple ring–moon cycles over the history of Mars.
Atmospheric CO2 levels varied across glacial–interglacial cycles. An analysis of ice-core CO2 identifies a lower limit to glacial CO2 concentrations, which may reflect a negative biosphere feedback to decreasing CO2 levels.
The radiative effect of desert dust depends in part on its size. An integrative analysis of observed and modelled dust size and abundance reveals that atmospheric dust is coarser, and less cooling, than previously thought.
The timing of onset of modern-style plate tectonics on Earth is unclear. Identification of eclogite rocks—typically formed during subduction—in the Trans-Hudson orogen implies modern-style tectonics may have been active 1,830 million years ago.