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<jats:p> The structure of ribosomal RNA (rRNA) in the ribosome was probed with hydroxyl radicals generated locally from iron(II) tethered to the 5′ ends of anticodon stem-loop analogs (ASLs) of transfer RNA. The ASLs, ranging in length from 4 to 33 base pairs, bound to the ribosome in a messenger RNA–dependent manner and directed cleavage to specific regions of the 16 <jats:italic>S</jats:italic> , 23 <jats:italic>S</jats:italic> , and 5 <jats:italic>S</jats:italic> rRNA chains. The positions and intensities of cleavage depended on whether the ASLs were bound to the ribosomal A or P site, and on the lengths of their stems. These data predict the three-dimensional locations of the rRNA targets relative to the positions of A- and P- site transfer RNAs inside the ribosome. </jats:p>

<jats:p> The age and origin of the moon have been studied with the use of the recently developed short-lived hafnium-tungsten chronometer ( <jats:sup>182</jats:sup> Hf- <jats:sup>182</jats:sup> W, half-life of nine million years). The tungsten isotopic compositions of 21 lunar samples range from chondritic to slightly radiogenic (ɛ <jats:sub>W</jats:sub> = −0.50 ± 0.60 to +6.75 ± 0.42). This heterogeneity may have been inherited from material excavated from Earth and the putative impactor, but it is more likely the result of late radioactive decay within the moon itself; in this case, the moon formed 4.52 to 4.50 billion years ago, and its mantle has since remained poorly mixed. </jats:p>

<jats:p>From November 1978 through December 1996, the areal extent of sea ice decreased by 2.9 ± 0.4 percent per decade in the Arctic and increased by 1.3 ± 0.2 percent per decade in the Antarctic. The observed hemispheric asymmetry in these trends is consistent with a modeled response to a carbon dioxide–induced climate warming. The interannual variations, which are 2.3 percent of the annual mean in the Arctic, with a predominant period of about 5 years, and 3.4 percent of the annual mean in the Antarctic, with a predominant period of about 3 years, are uncorrelated.</jats:p>

<jats:p>Many suboxic sediments and soils contain an Fe(II,III) oxide called green rust. Spectroscopic evidence showed that selenium reduces from an oxidation state of +VI to 0 in the presence of green rust at rates comparable with those found in sediments. Selenium speciation was different in solid and aqueous phases. These redox reactions represent an abiotic pathway for selenium cycling in natural environments, which has previously been considered to be mediated principally by microorganisms. Similar green rust–mediated abiotic redox reactions are likely to be involved in the mobility of several other trace elements and contaminants in the environment.</jats:p>

<jats:p> X-ray diffraction measurements indicate that ruby (Cr <jats:sup>3+</jats:sup> doped α-Al <jats:sub>2</jats:sub> O <jats:sub>3</jats:sub> ) transforms to the Rh <jats:sub>2</jats:sub> O <jats:sub>3</jats:sub> (II) structure when heated to temperatures exceeding ∼1000 kelvin at pressures above ∼100 gigapascals, in agreement with predictions from ab initio quantum mechanical calculations. The high-pressure phase did not quench upon decompression to ambient pressure, and the occurrence of this phase transformation may affect interpretations of static (diamond-anvil cell) and dynamic (shock-wave) experiments at ultra-high pressures. </jats:p>

<jats:p> In isotropic solution, internuclear dipolar couplings average to zero as a result of rotational diffusion. By dissolving macromolecules in a dilute aqueous nematic discotic liquid-crystalline medium containing widely spaced magnetically oriented particles, a tunable degree of solute alignment with the magnetic field can be created while retaining the high resolution and sensitivity of the regular isotropic nuclear magnetic resonance (NMR) spectrum. Dipolar couplings between <jats:sup>1</jats:sup> H- <jats:sup>1</jats:sup> H, <jats:sup>1</jats:sup> H- <jats:sup>13</jats:sup> C, <jats:sup>1</jats:sup> H- <jats:sup>15</jats:sup> N, and <jats:sup>13</jats:sup> C- <jats:sup>13</jats:sup> C pairs in such an oriented macromolecule no longer average to zero, and are readily measured. Distances and angles derived from dipolar couplings in human ubiquitin are in excellent agreement with its crystal structure. The approach promises to improve the accuracy of structures determined by NMR, and extend the size limit. </jats:p>

<jats:p>The sedimentary record of biogenic silica from Lake Baikal in south-central Siberia suggests that this region of central Asia was impacted by two major cooling episodes at 2.8 to 2.6 and 1.8 to 1.6 million years ago. The spectral evolution of this continental interior site parallels the evolutionary frequency spectra for various marine oxygen isotope records. In the Baikal record, the 41,000-year obliquity cycle is particularly strong from 1.8 to 0.8 million years ago; variance in the 100,000-year eccentricity band increases during the past 0.8 million years. The expected precession frequency of 23,000 years is highest during the past 400,000 years. The modulation of the predicted 23,000- and 41,000-year insolation forcing by the 100,000- and 400,000-year eccentricity bands indicates that the transfer of variance from the precession and obliquity frequencies to the eccentricity part of the spectrum occurred in the Eurasian continental interior, as well as in tropical and high-latitude ocean sites.</jats:p>

<jats:p>Rain forest fragments in central Amazonia were found to experience a dramatic loss of above-ground tree biomass that is not offset by recruitment of new trees. These losses were largest within 100 meters of fragment edges, where tree mortality is sharply increased by microclimatic changes and elevated wind turbulence. Permanent study plots within 100 meters of edges lost up to 36 percent of their biomass in the first 10 to 17 years after fragmentation. Lianas (climbing woody vines) increased near edges but usually compensated for only a small fraction of the biomass lost as a result of increased tree mortality.</jats:p>