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The Grand Canyon is one of the most dramatic features on Earth, yet when and why it was carved have been controversial topics for more than 150 years. Here, we present apatite 4He/³He thermochronometry data from the Grand Canyon basement that tightly constrain the near-surface cooling history associated with canyon incision. 4He/³He spectra for eastern Grand Canyon apatites of differing He date, radiation damage, and U-Th zonation yield a self-consistent cooling history that substantially validates the He diffusion kinetic model applied here. Similar data for the western Grand Canyon provide evidence that it was excavated to within a few hundred meters of modern depths by ~70 million years ago (Ma), in contrast to the conventional model in which the entire canyon was carved since 5 to 6 Ma. [ABSTRACT FROM AUTHOR]

Objective: To evaluate the effectiveness of a school nutrition programme on the weight gain and growth of Vietnamese schoolchildren.Design: A proximate cluster evaluation of children in seven schools, in which fortified milk and biscuits supplying 300 kcal of energy were being given on school days, compared with children in 14 nearby schools with no feeding. All children were dewormed.Setting: Twenty-one primary schools in Dong Thap Province, Vietnam.Subjects: A cohort of 1080 children in grade 1 of 21 primary schools, and a cross-sectional interview of 400 children in grade 3.Results: The programme gave children the equivalent of 90 kcal day- 1 over 17 months. t-Tests showed a small but statistically significant difference between groups in their average gain in weight and height: 3.19 versus 2.95 kg (P < 0.001) and 8.15 versus 7.88 cm (P = 0.008). A multiple-level model showed that the programme was statistically significant after controlling for clustering of children in schools, sex, age and initial underweight (P = 0.024). A significant impact on height was also seen in a regression model, but not when controlling for school. The most undernourished children tended to gain the least weight. There was no evidence of substitution.Conclusion: The programme had a small but significant effect on weight gain, but the most undernourished children benefited the least. Methods need to be developed to target them. This design may offer a means of estimating the impact of school feeding on growth in other programme settings. [ABSTRACT FROM AUTHOR]

Cosmogenic He-3 was measured in apatite, titanite, and zircon and cosmogenic Ne-21 in quartz at 13 depth intervals in a 2.7-m long drill core in a Miocene ignimbrite from the Altiplano of Bolivia. All three He-3 depth profiles as well as the Ne-21 profile attenuate exponentially with depth, indicating that both of these isotopes are cosmogenic in origin with no significant contribution from other sources. The attenuation lengthscale for He-3 production of Lambda=180 +/- 11 g/cm(2) is consistent with expectations for neutron spallation, and is identical to that found for the cosmogenic Ne-21 in quartz. By normalizing the measured He-3 concentrations to Ne-21 and using the independently known cosmogenic Ne-21 production rate, the apparent cosmogenic He-3 production rates in apatite, titanite, and zircon were respectively found to be 112, 97, and 87 atoms/g/yr at sea-level and high latitude. The formal uncertainty on these estimates is similar to 20% (2 sigma), and arises in equal parts from uncertainties in the measured He-3/Ne-21 ratios and the uncertainty in the Ne-21 production rate. However an additional factor affecting the apparent He-3 production rate in these phases arises from the long stopping range of spalled He-3 and tritium (which decays to He-3). Because all three accessory phases have higher mean atomic number than major rock-forming minerals, they will have lower He-3 production rates than their surroundings. As a consequence the long stopping ranges will cause a net implantation of He-3 and therefore higher apparent production rates than would apply for purely in-situ production. Thus these apparent production rates apply only to the specific grain sizes analyzed. Analysis of sieved zircon aliquots suggests that a factor of 2 increase in grain size (from similar to 50 to similar to 100 mu m cross-section) yields a 10% decrease in apparent production rate. While this effect warrants further study, the grain sizes analyzed here are typical of the accessory phases commonly encountered, so the apparent rates provide an appropriate starting place for surface exposure dating using He-3 in these minerals., Earth and Planetary Sciences

Helium concentration and isotopic composition were measured in a suite of samples across the Permian–Triassic boundary at Opal Creek, Canada, to determine whether high extraterrestrial helium concentrations are associated with a possible extinction-inducing impact event at this time. No extraterrestrial [super]3He was detected, implying that neither fullerene-hosted nor IDP-hosted He is present at or near the boundary. This observation is consistent with similar studies of some Permian–Triassic sections, but contrasts sharply with reports of both fullerene- and IDP-hosted extraterrestrial [super]3He at other sections. Step-heat experiments indicate rapid diffusion of extraterrestrial helium from sediments heated to temperatures above ~70 °C. Given the likelihood of burial and associated heating in Permian–Triassic age rocks, the initially unexpected absence of IDP-hosted [sup]3He likely indicates thermally induced diffusive loss. Indeed one of the key sections (Graphite Peak, Antarctica) from which extraterrestrial [super]3He has been reported at and near the Permian–Triassic boundary has been sufficiently heated that the reported preservation of extraterrestrial helium, in both IDPs and fullerenes, is inexplicable. Recent contamination provides a plausible explanation for extraterrestrial [super]3He in these samples. While no extraterrestrial [sup]3He was detected at Opal Creek, there is a sharp increase in nucleogenic [super]3He very close to or at the Permian–Triassic boundary. This presumably arises from the major lithologic change at this time, from cherts in the Permian to shales and siltstones in the Triassic. Increased nucleogenic [super]3He is associated with increases in both lithium and organic carbon content into the Triassic. Either the production rate or the retention of this [super]3He is higher in the shales and siltstones than in the cherts. Care must be taken to eliminate such artifacts before interpreting changes in [super]3He concentration in terms of fluctuations in the delivery of [super]3He from space., Earth and Planetary Sciences

There is acidaemia (low pH), respiratory acidosis (high Paco SB 2 sb ) and metabolic alkalosis (high There is a very severe acidaemia (low pH) with respiratory alkalosis (low Paco SB 2 sb ) and metabolic acidosis (low 15 mmol/L, Na SP + sp 147 mmol/L, K SP + sp 7 mmol/L, Cl SP - sp 95 mmol/L. There is very mild acidaemia (low pH) with respiratory alkalosis (low Paco SB 2 sb ) and metabolic acidosis (low In this case, there are three concomitant disorders: respiratory alkalosis, HAGMA and metabolic alkalosis. [Extracted from the article]