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<jats:p>Uranium-thorium isotope results from island arc volcanic rocks were used to investigate the rates of transfer of fluids and sediments from the downgoing slab. Uranium, but not thorium, is readily mobilized in the fluid. A negative array between thorium/cerium and neodymium-143/neodymium-144 indicates that significant amounts of the thorium in arc rocks are derived from subducted sediments, although perhaps only about 30 percent of the thorium in subducted sediments is returned to the crust in this way. The transfer times for fluid through the mantle wedge are about 30,000 to 120,000 years, whereas those for sediment melts may be several million years. The low average uranium/thorium ratios of bulk crust primarily reflect different crustal generation processes in the Archaean.</jats:p>

<jats:p>A high-resolution gravity field of poorly charted and ice-covered ocean near West Antarctica, from the Ross Sea east to the Weddell Sea, has been derived with the use of satellite altimetry, including ERS-1 geodetic phase, wave-form data. This gravity field reveals regional tectonic fabric, such as gravity lineations, which are the expression of fracture zones left by early (65 to 83 million years ago) Pacific-Antarctic sea-floor spreading that separated the Campbell Plateau and New Zealand continent from West Antarctica. These lineations constrain plate motion history and confirm the hypothesis that Antarctica behaved as two distinct plates, separated from each other by an extensional Bellingshausen plate boundary active in the Amundsen Sea before about 61 million years ago.</jats:p>

<jats:p> Telomerase is a ribonucleoprotein enzyme essential for the replication of chromosome termini in most eukaryotes. Telomerase RNA components have been identified from many organisms, but no protein component has been demonstrated to catalyze telomeric DNA extension. Telomerase was purified from <jats:italic>Euplotes aediculatus</jats:italic> , a ciliated protozoan, and one of its proteins was partially sequenced by nanoelectrospray tandem mass spectrometry. Cloning and sequence analysis of the corresponding gene revealed that this 123-kilodalton protein (p123) contains reverse transcriptase motifs. A yeast ( <jats:italic>Saccharomyces cerevisiae</jats:italic> ) homolog was found and subsequently identified as <jats:italic>EST2</jats:italic> (ever shorter telomeres), deletion of which had independently been shown to produce telomere defects. Introduction of single amino acid substitutions within the reverse transcriptase motifs of Est2 protein led to telomere shortening and senescence in yeast, indicating that these motifs are important for catalysis of telomere elongation in vivo. In vitro telomeric DNA extension occurred with extracts from wild-type yeast but not from <jats:italic>est2</jats:italic> mutants or mutants deficient in telomerase RNA. Thus, the reverse transcriptase protein fold, previously known to be involved in retroviral replication and retrotransposition, is essential for normal chromosome telomere replication in diverse eukaryotes. </jats:p>

<jats:p> Gases trapped in individual vesicles in the volatile-rich basaltic glass “popping rock” were found to have the same carbon dioxide, helium-4, and argon-40 composition, but a variable <jats:sup>40</jats:sup> Ar/ <jats:sup>36</jats:sup> Ar ratio (∼4000 to ≥40,000). The argon-36 is probably surface-adsorbed atmospheric argon; any mantle argon-36 trapped in the vesicles cannot be distinguished from an atmospheric contaminant. Consequently the <jats:sup>40</jats:sup> Ar/ <jats:sup>36</jats:sup> Ar ratios and <jats:sup>3</jats:sup> He/ <jats:sup>36</jats:sup> Ar ratios (1.45) determined are minimum estimates of the upper mantle composition. Heavy noble gas relative abundances in the mantle resemble solar noble gas abundance patterns, and a solar origin may be common to all primordial mantle noble gases. </jats:p>

<jats:p>The interaction between tectonism and erosion produces rugged landscapes in actively deforming regions. In the northwestern Himalaya, the form of the landscape was found to be largely independent of exhumation rates, but regional trends in mean and modal elevations, hypsometry (frequency distribution of altitude), and slope distributions were correlated with the extent of glaciation. These observations imply that in mountain belts that intersect the snowline, glacial and periglacial processes place an upper limit on altitude, relief, and the development of topography irrespective of the rate of tectonic processes operating.</jats:p>

<jats:p>Crystal engineering of molecular materials is commonly frustrated by the absence of reliable structural paradigms that are needed for systematic design of crystal lattices with predictable structure and desirable function. This problem can be attributed, at least partially, to the absence of robust supramolecular motifs that serve as synthons for the assembly of crystal lattices. A novel class of molecular crystals based on two-dimensional hydrogen (H)-bonded networks comprising guanidinium ions and the sulfonate groups of alkane- or arenedisulfonate ions is described. The disulfonate ions act as pillars that connect opposing H-bonded sheets and form nanoporous galleries with one-dimensional channels. The flexibility of the H-bonded network allows the galleries to adapt to changes in the steric requirements of guest molecules that occupy the channels. This robustness reduces crystal engineering to the last remaining dimension, enabling rational adjustment of the gallery heights by choice of the disulfonate pillar.</jats:p>

<jats:p> A single-electron transistor scanning electrometer (SETSE)—a scanned probe microscope capable of mapping static electric fields and charges with 100-nanometer spatial resolution and a charge sensitivity of a small fraction of an electron—has been developed. The active sensing element of the SETSE, a single-electron transistor fabricated at the end of a sharp glass tip, is scanned in close proximity across the sample surface. Images of the surface electric fields of a GaAs/Al <jats:sub> <jats:italic>x</jats:italic> </jats:sub> Ga <jats:sub>1−</jats:sub> <jats:sub> <jats:italic>x</jats:italic> </jats:sub> As heterostructure sample show individual photo-ionized charge sites and fluctuations in the dopant and surface-charge distribution on a length scale of 100 nanometers. The SETSE has been used to image and measure depleted regions, local capacitance, band bending, and contact potentials at submicrometer length scales on the surface of this semiconductor sample. </jats:p>

<jats:p>A paleosol in the Middle Devonian Aztec Siltstone of Victoria Land, Antarctica, is the most ancient known soil of well-drained forest ecosystems. Clay enrichment and chemical weathering of subsurface horizons in this and other Devonian forested paleosols culminate a long-term increase initiated during the Silurian. From Silurian into Devonian time, red clayey calcareous paleosols show a greater volume of roots and a concomitant decline in the density of animal burrows. These trends parallel the decline in atmospheric carbon dioxide determined from isotopic records of pedogenic carbonate in these same paleosols. The drawdown of carbon dioxide began well before the Devonian appearance of coals, large logs, and diverse terrestrial plants and animals, and it did not correlate with temporal variation in volcanic or metamorphic activity. The early Paleozoic greenhouse may have been curbed by the evolution of rhizospheres with an increased ratio of primary to secondary production and by more effective silicate weathering during Silurian time.</jats:p>

<jats:p>Spinal cord injuries result in paralysis, because when damaged neurons die they are not replaced. Neurogenesis of electrophysiologically functional neurons occurred in spinal cord cultured from postnatal rats. In these cultures, the numbers of immunocytochemically identified neurons increased over time. Additionally, neurons identified immunocytochemically or electrophysiologically incorporated bromodeoxyuridine, confirming they had differentiated from mitotic cells in vitro. These findings suggest that postnatal spinal cord retains the capacity to generate functional neurons. The presence of neuronal precursor cells in postnatal spinal cord may offer new therapeutic approaches for restoration of function to individuals with spinal cord injuries.</jats:p>

<jats:p>The gene encoding the BCL-6 transcriptional repressor is frequently translocated and mutated in diffuse large cell lymphoma. Mice with a disrupted BCL-6 gene developed myocarditis and pulmonary vasculitis, had no germinal centers, and had increased expression of T helper cell type 2 cytokines. The BCL-6 DNA recognition motif resembled sites bound by the STAT (signal transducers and activators of transcription) transcription factors, which mediate cytokine signaling. BCL-6 could repress interleukin-4 (IL-4)–induced transcription when bound to a site recognized by the IL-4–responsive transcription factor Stat6. Thus, dysregulation of STAT-responsive genes may underlie the inflammatory disease in BCL-6–deficient mice and participate in lymphoid malignancies.</jats:p>