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<jats:p> Can the time, location, and magnitude of future earthquakes be predicted reliably and accurately? In their Perspective, Geller <jats:italic>et al</jats:italic> .'s answer is “no.” Citing recent results from the physics of nonlinear systems “chaos theory,” they argue that any small earthquake has some chance of cascading into a large event. According to research cited by the authors, whether or not this happens depends on unmeasurably fine details of conditions in Earth's interior. Earthquakes are therefore inherently unpredictable. Geller <jats:italic>et al</jats:italic> . suggest that controversy over prediction lingers because prediction claims are not stated as objectively testable scientific hypotheses, and due to overly optimistic reports in the mass media. </jats:p>

<jats:p>Lack of a 19th-century baseline temperature against which 20th-century warming can be referenced constitutes a deficiency in understanding recent climate change. Combination of borehole temperature profiles, which contain a memory of surface temperature changes in previous centuries, with the meteorological archive of surface air temperatures can provide a 19th-century baseline temperature tied to the current observational record. A test case in Utah, where boreholes are interspersed with meteorological stations belonging to the Historical Climatological Network, yields a noise reduction in estimates of 20th-century warming and a baseline temperature that is 0.6° ± 0.1°C below the 1951 to 1970 mean temperature for the region.</jats:p>

<jats:p> An iron-sulfur compound (Fe <jats:sub>3</jats:sub> S <jats:sub>2</jats:sub> ) was synthesized at pressures greater than 14 gigapascals in the system Fe-FeS. The formation of Fe <jats:sub>3</jats:sub> S <jats:sub>2</jats:sub> changed the melting relations from a simple binary eutectic system to a binary system with an intermediate compound that melted incongruently. The eutectic temperature in the system at 14 gigapascals was about 400°C lower than that extrapolated from Usselman's data, implying that previous thermal models of Fe-rich planetary cores could overestimate core temperature. If it is found in a meteorite, the Fe <jats:sub>3</jats:sub> S <jats:sub>2</jats:sub> phase could also be used to infer the minimum size of a parent body. </jats:p>

<jats:p> The lower mantle of the Earth is believed to be largely composed of (Mg,Fe)O (magnesiowüstite) and (Mg,Fe)SiO <jats:sub>3</jats:sub> (perovskite). Radiative temperatures of single-crystal olivine [(Mg <jats:sub>0.9</jats:sub> ,Fe <jats:sub>0.1</jats:sub> ) <jats:sub>2</jats:sub> SiO <jats:sub>4</jats:sub> ] decreased abruptly from 7040 ± 315 to 4300 ± 270 kelvin upon shock compression above 80 gigapascals. The data indicate that an upper bound to the solidus of the magnesiowüstite and perovskite assemblage at 4300 ± 270 kelvin is 130 ± 3 gigapascals. These conditions correspond to those for partial melting at the base of the mantle, as has been suggested occurs within the ultralow-velocity zone beneath the central Pacific. </jats:p>

<jats:p>Strong, scattered reflections beyond 8 degrees (8°) offset are characteristic features of all high-resolution seismic sections from the continents. The reflections identify a low-velocity zone below approximately 100 kilometers depth beneath generally stratified mantle. This zone may be caused by partial melting, globally initiated at equal depth in the continental mantle. Solid state is again attained at the Lehmann discontinuity in cold, stable areas, whereas the zone extends to near the 400-kilometer discontinuity in hot, tectonically active areas. Thus, the depth to the Lehmann discontinuity may be an indicator of the thermal state of the continental mantle.</jats:p>

<jats:p>Indirect evidence for life on Mars has been reported from the study of meteorite ALH84001. The formation temperature of the carbonates is controversial; some estimates suggest 20° to 80°C, whereas others exceed 650°C. Paleomagnetism can be used to distinguish between these possibilities because heating can remagnetize ferrimagnetic minerals. Study of two adjacent pyroxene grains from the crushed zone of ALH84001 shows that each possesses a stable natural remanent magnetization (NRM), implying that Mars had a substantial magnetic field when the grains cooled. However, NRM directions from these particles differ, implying that the meteorite has not been heated significantly since the formation of the internal crushed zone about 4 billion years ago. The carbonate globules postdate this brecciation, and thus formed at low temperatures.</jats:p>

<jats:p> The martian meteorite ALH84001 contains small, disk-shaped concretions of carbonate with concentric chemical and mineralogical zonation. Oxygen isotope compositions of these concretions, measured by ion microprobe, range from δ <jats:sup>18</jats:sup> O = +9.5 to +20.5‰. Most of the core of one concretion is homogeneous (16.7 ± 1.2‰) and over 5‰ higher in δ <jats:sup>18</jats:sup> O than a second concretion. Orthopyroxene that hosts the secondary carbonates is isotopically homogeneous (δ <jats:sup>18</jats:sup> O = 4.6 ± 1.2‰). Secondary SiO <jats:sub>2</jats:sub> has δ <jats:sup>18</jats:sup> O = 20.4‰. Carbon isotope ratios measured from the core of one concretion average δ <jats:sup>13</jats:sup> C = 46 ± 8‰, consistent with formation on Mars. The isotopic variations and mineral compositions offer no evidence for high temperature (&gt;650°C) carbonate precipitation and suggest non-equilibrium processes at low temperatures (&lt;∼300°C). </jats:p>

<jats:p> Femtosecond laser pulses and coherent two-phonon Raman scattering were used to excite KTaO <jats:sub>3</jats:sub> into a squeezed state, nearly periodic in time, in which the variance of the atomic displacements dips below the standard quantum limit for half of a cycle. This nonclassical state involves a continuum of transverse acoustic modes that leads to oscillations in the refractive index associated with the frequency of a van Hove singularity in the phonon density of states. </jats:p>

<jats:p>Axonal pathfinding in the nervous system is mediated in part by cell-to-cell signaling events involving members of the Eph receptor tyrosine kinase (RTK) family and their membrane-bound ligands. Genetic evidence suggests that transmembrane ligands may transduce signals in the developing embryo. The cytoplasmic domain of the transmembrane ligand Lerk2 became phosphorylated on tyrosine residues after contact with the Nuk/Cek5 receptor ectodomain, which suggests that Lerk2 has receptorlike intrinsic signaling potential. Moreover, Lerk2 is an in vivo substrate for the platelet-derived growth factor receptor, which suggests crosstalk between Lerk2 signaling and signaling cascades activated by tyrosine kinases. It is proposed that transmembrane ligands of Eph receptors act not only as conventional RTK ligands but also as receptorlike signaling molecules.</jats:p>

<jats:p> The organization of calcium (Ca <jats:sup>2+</jats:sup> ) stores in the sarcoplasmic and endoplasmic reticulum (S-ER) is poorly understood. The dynamics of the storage and release of calcium in the S-ER of intact, cultured astrocytes and arterial myocytes were studied with high-resolution imaging methods. The S-ER appeared to be a continuous tubular network; nevertheless, calcium stores in the S-ER were organized into small, spatially distinct compartments that functioned as discrete units. Cyclopiazonic acid (an inhibitor of the calcium pump in the S-ER membrane) and caffeine or ryanodine unloaded different, spatially separate compartments. Heterogeneity of calcium stores was also revealed in cells activated by physiological agonists. These results suggest that cells can generate spatially and temporally distinct calcium signals to control individual calcium-dependent processes. </jats:p>