Volume 2 Issue 10, October 2009

Greenhouse-gas emissions keep rising, despite all efforts at regulation and international agreement. Geoengineering could provide a back-up plan.

Charles Darwin became the founder and mythic hero of modern evolutionary biology with the publication of his work On the Origin of Species 150 years ago. The book bears the signature of a geological thinker who had turned to a faster-moving discipline.

Conflicting proxies for the size of early Antarctic ice sheets have been puzzling. A reconstruction of West Antarctica's past elevation suggests that the disagreement stems from an underestimation of Antarctica's surface area above sea level.

Palaeomagnetists' basic assumption that Earth's magnetic field is a GAD, that is, a geocentric axial dipole, has been challenged by anomalous magnetic data from ancient Canadian basalts. At a closer look, fast continental drift could explain this anomaly.

Forest fires convert a small portion of burning vegetation into charred solid residues such as charcoal. A survey of Scandinavian forest soils reveals that charcoal has a highly patchy distribution, and a shorter-than-expected lifetime.

During an earthquake, friction is a key control on the initiation, propagation and termination of fault motion. Laboratory experiments that use variable slip rates suggest that friction evolves in a more complex fashion than generally assumed.

As the Earth warms, the overturning circulation of the upper atmosphere is projected to speed up. Model simulations suggest that this will increase the flux of ozone from the stratosphere to the troposphere, and alter surface levels of ultraviolet radiation.

Many of the world's deltas are densely populated and intensively farmed. An assessment of recent publications indicates that the majority of these deltas have been subject to intense flooding over the past decade, and that this threat will grow as global sea-level rises and as the deltas subside.

Now that stratospheric ozone depletion has been controlled by the Montreal Protocol, interest has turned to the effects of climate change on the ozone layer. An atmospheric chemistry model suggests that climate change will increase the stratosphere-to-troposphere ozone flux by 23% globally between 1965 and 2095, altering the amount of ultraviolet radiation reaching Earth’s surface.

Forest fires release significant amounts of carbon dioxide into the atmosphere, but also convert a fraction of the burning vegetation to charred black carbon. Examination of 845 soil samples in Scandinavian forests shows that the charcoal content of boreal soils is highly variable, and more susceptible to degradation than has been thought.

Phosphonates, compounds with a carbon–phosphorus bond, are a key component of the marine-dissolved organic phosphorus pool. Nuclear magnetic resonance spectroscopy measurements suggest that the cyanobacteria Trichodesmium is a significant source of phosphonates in nutrient-poor regions of the ocean.

Earthquakes often occur in areas that lack an array of seismometers, resulting in a scarcity of local measurements from some regions of great geological interest. In such regions, some earthquakes themselves may be turned into virtual seismometers that are capable of measuring strain caused by passing waves from other earthquakes.

The dynamic friction along faults controls earthquake ruptures in the crust, but many previous studies have quantified this value only for constant slip rates. Experiments accounting for the more realistic condition of changing slip rates suggest that faults undergo a sequence of strengthening, weakening and healing during acceleration and deceleration of slip.

Rocks near the San Andreas fault are pervasively crushed at distances of up to 400 m from its core. Laboratory experiments and calculations suggest that the rocks were pulverized at high strain rates (>150 s⁻¹) associated with a supershear rupture—a rupture propagating at a velocity equal to greater than that of seismic shear waves.

1.1-billion-year-old volcanic rocks in North America are thought to record asymmetric geomagnetic reversals, indicating non-axial dipolar behaviour of the magnetic field. High-resolution data from Ontario suggest that the reversals were instead symmetric, and that the apparent reversal asymmetry is an aliasing effect of the low resolution of earlier samples combined with the rapid motion of North America.

The devastating Wenchuan earthquake in 2008 struck along a fault zone that showed low rates of deformation. Analysis of GPS and InSAR data suggests that, as structural barriers failed during a single earthquake, the rupture cascaded across multiple fault segments, which may explain the high magnitude of the event.

The initial production of oxygen in early Earth’s oceans altered the redox chemistry and cycling of nitrogen. A record of nitrogen isotopes from preserved organic matter indicates nitrogen cycling in the presence of free oxygen 2.67 billion years ago, about 200 million years before the first geochemical evidence for atmospheric free oxygen.