February 2014 -- Asteroids: Linking Meteorites and Planets
At present, we know of ~600,000 asteroids in the asteroid belt, and there are very likely millions more. Orbiting the Sun between Mars and Jupiter, they are thought to be the shattered remnants of small bodies formed within the young Sun's solar nebula that never accreted enough material to become planets. These “minor bodies” are therefore keys to understanding how the Solar System formed and evolved. As leftover planetary building blocks, they are of great importance in understanding planetary compositions. They may also provide clues to the origin of life, as similar bodies may have delivered organics and water to the early Earth. For these reasons, several international space agencies have funded sample- return missions to asteroids.
This thematic issue will cover some of the most exciting advances in ophiolite science. Focus is directed toward ophiolite classification during the formation and destruction of ocean basins; the mineralogy, petrology, and isotope geochemistry of ophiolites; and the trace element behavior of crustal and upper-mantle units in ophiolites. The issue will cover the history of origin, the geochemical and petrological development, and the final emplacement of one of the largest and most studied ophiolites, the classical Semail ophiolite in Oman. Further, for a better understanding of ophiolites in relation to subduction processes, one of the papers deals with the lithological and geochemical development of the Izu-Bonin-Mariana forearc crust as a modern analogue. Finally, the issue will present some of the new and exciting aspects of microbial interaction with the volcanic component of oceanic crust, as observed in ophiolites as old as the young Earth.
The issue on kaolin illustrates admirably how materials known and used since the dawn of humanity may still have many surprises in store for us in terms of new uses and applications. Guest Editors Paul Schroeder and David Bish chose to present the whole spectrum of uses of kaolin, from ancient porcelains to nanocomposites. Kaolin-group minerals are among the most important industrial clay minerals, with a worldwide consumption in the millions of tons per year and applications in a wide range of industrial areas. Traditionally, their most important use has been in the paper and ceramic industries. New, innovative techniques have now allowed the synthesis of kaolinite–polymer nanocomposites, including bionanocomposites.
Unconventional hydrocarbons, such as gas and oil shale, oil sands, and heavy oil, can now be exploited more effectively and economically. This has stimulated exploration and exploitation on a global scale and has led to a new economic and environmental landscape in energy matters. Exploiting unconventional hydrocarbons requires additional technology, energy, and capital compared to the industry standard. In this thematic issue, Guest editors David Cole and Michael Arthur address the geologic and geochemical nature of these resources and their impact on global socioeconomics and the environment.
Cosmogenic nuclides illustrate a frontier area that is fast moving thanks to improvements in analytical instrumentation. It is interesting to see that theoretical developments in particle physics have found applications in our effort to understand today’s landscapes. Guest editors Friedhelm von Blanckenburg and Jane Willenbring, together with the cast of authors they assembled, chose to illustrate how cosmogenic nuclides can help us understand Earth-surface processes. And the Toolkit article shows off the technological prowess needed to measure these rare nuclides—one atom in a million billion.
Graphitic carbon, with its diverse structures and unique properties, is everywhere at the Earth’s surface. Strategically located at the interface between the lithosphere, biosphere, hydrosphere, and atmosphere, graphitic carbon constitutes a major terrestrial carbon reservoir. Natural and synthetic graphitic carbon is also used in a broad range of applications. Graphitic carbon has played an important role in human history (for example, coal mining) and is now a building block of nanotechnology, but this remarkable material is also an active player in geological processes. From Beyssac and Rumble, Elements 10: 415-420.