Volume 5 Issue 2, February 2012

The Late Ordovician period, ending 444 million years ago, was marked by the onset of glaciations. The expansion of non-vascular land plants accelerated chemical weathering and may have drawn down enough atmospheric carbon dioxide to trigger the growth of ice sheets.

The influence of trees and dead wood on river dynamics has long been overlooked. Recent work suggests that large wood pieces can stabilize the land surface, contributing to a large-wood cycle that profoundly affects floodplain morphology and ecology.

Models predict that mercury undergoes rapid oxidation in the upper atmosphere. Aircraft measurements support this prediction and provide evidence for a previously unrecognized sink for stratospheric mercury.

Toxic heavy metals can accumulate in Earth's near surface to form ore deposits. Experimental and direct measurements of ore fluids reveal the efficient mobilization and deposition of uranium, implying potentially rapid formation of economic-grade ore.

Rivers draining the Himalaya provide vital resources for almost half of the world's population. A combined model–data analysis suggests that the contribution of groundwater to the annual water budget in the central Himalaya may be substantial.

Throughout the Palaeozoic era, about 540 to 250 million years ago, plants colonized land and rapidly diversified. An analysis of the palaeontologic record shows that this diversification irrevocably altered the shape and form of fluvial systems.

Saturn’s moon Titan has a dense atmosphere, but its thermal structure is poorly understood. Simulations with a three-dimensional general circulation model suggest that Titan has a lower atmospheric structure with two boundary layers: a seasonal deep layer, and a shallower one that develops during the course of each day.

Global climate change results from a small yet persistent imbalance between the amount of sunlight absorbed by the Earth and the thermal radiation emitted back to space. A revised analysis of measured changes in the net radiation imbalance at the top of the atmosphere, and the ocean heat content to a depth of 1,800 m, suggests that these two sets of observations are consistent within error margins.

Mercury contamination affects many aquatic ecosystems. Measurements of mercury concentrations in air of stratospheric origin suggest that mercury is oxidized in the stratosphere and subsequently lost to the troposphere, most likely following attachment to stratospheric particles.

Atmospheric aerosols affect cloud properties, and thereby the radiative balance of the planet and the water cycle. An analysis of satellite data suggests that increases in aerosol abundance are associated with local intensification of rain rates over land and ocean.

Humid montane tropical forests are often thought to contain low levels of bioavailable nitrogen. An analysis of the concentration and isotopic signature of nitrate in tropical montane forest streams suggests that these ecosystems may be rich in nitrogen.

In the course of the transfer of precipitation into rivers, water is temporarily stored in reservoirs with different residence times. Analyses of precipitation and discharge records from Nepal suggest that in addition to snow and glacier melt and evapotranspiration, groundwater storage in a fractured basement aquifer also affects the annual discharge cycle of Himalayan rivers.

In the roots of the ocean crust, mantle-derived rocks are progressively hydrated by hydrothermal circulation. Raman spectroscopic analyses of hydrated rocks sampled from the ocean floor reveal accumulations of organic matter, which point to the hydration process as a possible energy source.

The length of time the present interglacial would last in the absence of anthropogenic forcing is debated. An alignment of the Holocene and MIS 19c on the basis of the occurrence of the bipolar seesaw suggests that the present interglacial would last another 1,500 years, provided atmospheric CO₂ concentrations fell below 240 parts per million by volume.

The Athabasca Basin, Canada, is home to some of the world’s largest uranium deposits. Analysis of preserved ore-forming fluids and experimental measurement of uranium solubility in analogous solutions show that the giant deposits could have formed relatively rapidly from extremely uranium-rich brines under acidic conditions.

In the westernmost Himalaya, the Indian Plate is thought to slip beneath the Potwar and Kohat plateaux on a layer of viscous material in an entirely aseismic manner. Analysis of InSAR data from 1992 shows that slip occurred during a rare M_w 6.0 earthquake, implying that the Kohat Plateau is locally grounded.

Ocean warming during the last deglaciation decreased the solubility of oxygen. A global compilation of marine sediment records shows that the deglacial trend of deoxygenation was overprinted by changes in ocean circulation and marine productivity.

Vegetation has been a key part of the Earth's surface for only about 450 million years. With the progression of the terrestrial landscape from bare surfaces to widespread coverage by plants - ground vegetation initially, then trees and finally flowering plants - the Earth's surface and its biogeochemical processes have also changed. In this issue, we present a collection of articles that explore how the evolution of terrestrial plants and the Earth's surface have affected each other.