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The primitive Moon was covered with a thick layer of melt known as the lunar magma ocean, whose crystallization resulted in the Moon’s surface as it is observed today. Dating of the oldest zircon so far in lunar rocks indicates that much of the magma was probably crystallized within 100 million years of the Moon’s formation.
The conditions leading to rock failure during intermediate-depth earthquakes in subduction zones are not clear, particularly in the absence of free fluid. Field observations and numerical simulations indicate that thermal weakening due to high-temperature shear instabilities may trigger earthquakes under such circumstances.
Continued global warming could persist far into the future, because natural processes require decades to hundreds of thousands of years to remove carbon dioxide produced by fossil-fuel burning from the atmosphere. A 100,000-year simulation indicates that severe ocean oxygen depletion could last for thousands of years.
Field studies and experimental research during the past two decades have provided considerable evidence for a significant influence of climate on tectonics. Recent advances suggest that model predictions can guide future fieldwork aimed at substantiating this view.
Photochemical ozone production near the Earth’s surface is considered to be a summertime, urban phenomenon. However, air-quality measurements in the rural Upper Green River Basin, Wyoming, show rapid, diurnal photochemical production of ozone during air temperatures as low as −17 ∘C.
Stress accumulation between earthquakes results from slip that is insufficient to fully accommodate plate movement. An inverse analysis of GPS data from the Kuril–Japan trench reveals a trench-parallel belt of stress accumulation with six peaks in the depth range of 10–40 km, suggesting potential source regions for future earthquakes.
Surface solar radiation has undergone decadal variations, producing global ‘dimming’ and ‘brightening’ effects, probably owing to changes in aerosol burden and clouds. An analysis of multidecadal data of horizontal visibility shows that the occurrence of fog, mist and haze has declined in Europe over the past 30 years.
The carbon cycle plays a central role in climate change. An analytical framework shows that the influence of atmospheric carbon dioxide concentrations on climate is more sensitive to carbon perturbations now than it has been over much of the preceding 400 million years.
A quantitative reconstruction of the global climate during the last glacial maximum was published in the early 1980s. A synthesis of global sea-surface temperature reconstructions shows global cooling of the tropical oceans and strong longitudinal temperature-gradients.
Methylmercury bioaccumulates in aquatic food chains and can cross the blood–brain barrier, making this organometallic compound a much more worrisome pollutant than inorganic mercury. Experimental evidence now indicates that mercury methylation by the bacterium Geobacter sulfurreducens can be greatly enhanced in the presence of the amino-acid cysteine.
The recent, dramatic retreat of many outlet glaciers of the Greenland ice sheet has raised concerns over Greenland’s contribution to future sea-level rise. Simulations with a numerical ice-flow model indicate that the recent rates of mass loss in Greenland’s outlet glaciers are transient and should not be extrapolated into the future.
The oceans soak up a large fraction of the carbon dioxide we emit into the atmosphere. The long-term strength and efficiency of this carbon sink relies on the transport of surface waters to the deep ocean.
Climate models predict that increasing greenhouse gas levels will invigorate the circulation in the upper atmosphere. But a close look at observations of the age of stratospheric air over 30 years reveals no acceleration in the circulation.
Meteorites frequently bombarded the surface of the early Earth. Could these impacts have provided the energy and materials to form the basic building blocks of life?
