Earth and Planetary Science
EPS Near-Surface Geochemistry and Geobiology

Research Spotlights

In their recently published paper in Science (reprint), recent EPS Ph.D. graduate John Moreau and Prof. Jill Banfield, along with colleagues from Lawrence Berkeley and Lawrence Livermore National Labs, demonstrated the presence of extracellular biofilm proteins inside bacterially-formed aggregates of nanocrystalline zinc-sulfide (orange and yellow features in image). These proteins promoted the rapid aggregation of sulfide nanoparticles formed by bacterial sulfate reduction in an abandoned flooded mine, and thereby restricted the dispersal of contaminant metals such as zinc, arsenic and selenium. In nature, metal-binding proteins associated with sulfate-reducing bacteria or biofilm formation may serve to inhibit the mobility of nanoparticulate or colloidal toxic metals away from their source.

In their recently published paper in Nature (reprint), Taylor Perron, Jerry Mitrovica, Michael Manga, Isamu Matsuyama and Mark Richards argue that there were once oceans on Mars, but that Mars has tipped over since they dried up. The northern plains are ringed by surface features that look like relic shorelines. However, long-wavelength trends in their elevation argue against the shoreline hypothesis. In this new study it is shown that polar wander can explain the shoreline deformation.

In their recently published paper in Nature (reprint), Barbara Romanowicz and Federica Marone present their study of seismic anisotropy beneath the North American continent. Seismic anisotropy provides information about mineral orientations, which, in turn, can be related to flow in the mantle. Their study shows evidence for two layers of anisotropy. At asthenospheric depths, the fast axis is sub-parallel to the plate motion, confirming the presence of shear related to current tectonic processes, whereas within the lithosphere, the orientation is significantly different, indicating that anisotropy at these shallower depths was 'frozen-in' long ago.

In their recently published Science paper (reprint) Brett Baker and Jill Banfield and prior members of the Banfield group (Gene Tyson, Eric Allen, Judith Flanagan, Phil Hugenholtz), in collaboration with Rick Webb (Univeristy of Queensland), describe the discovery microbes on a novel branch on the tree of life. The archaeal organisms grow within acid mine drainage microbial communities that play a key role in metal sulfide mineral dissolution and acid mine drainage formation. These groups, named ARMAN, were overlooked by conventional microbiological methods (PCR and culturing). Surprisingly, these cells appear to be among the smallest yet described. The study shows how community genomic analyses can detect new lineages of organisms and facilitate their characterization, enhancing our understanding of the role of microorganisms in important geochemical processes.

Professors Inez Fung, Ronald Cohen, Donald DePaolo, William Dietrich and James Kirchner of the Dept. of Earth and Planetary Science have formed the Keck HydroWatch Center with Professor David Culler of the Dept. of Electrical Engineering and Computer Science. The new center will dramatically expand the observations of all aspects of the water cycle by developing cost-effective, rapid-response, and accurate sensors and techniques to monitor water quality, quantity, and pathways.

In their recent Science paper (reprint), S. Merkel, A. Kubo, L. Miyagi, S. Speziale, T. Duffy, H.-k. Mao, and Rudy Wenk investigate the deformation behavior of germanate post-perovskite at pressures beyond 100 GPa. From the pattern of preferred orientation they determine that slip (100) and (110) slip is dominant. With this experimental information they model seismic anisotropy at the core-mantle boundary and suggest that perovskite contributes about 4% to shear wave splitting in D", with an oblique polarization.

In their paper recently published in Nature (reprint) Bill Dietrich and Taylor Perron investigate the influence of biota on the processes controlling landscape form and evolution. They find that while the signatures of life are present at all scales, there is no single landform that uniquely reflects the presence of life. Listen to the Nature Podcast (segment starts at 16:30).

In a paper recently published in Nature (reprint) Erik Olson and Richard Allen report a scaling relation between the frequency content of the first few seconds of energy radiated from an earthquake rupture and its magnitude. These characteristics can be used to estimate the magnitude before the rupture is complete and provide a basis for an earthquake alarm system.

In a paper recently published in Science, graduate student Aimin Cao, Professor Barbara Romanowicz and collaborator Nozumu Takeuchi report on the to-date most clear detection and identification of PKJKP, the elusive seismic phase that travels as a shear wave through the inner core.

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