Purines and triazines in the Murchison meteorite

Two samples of the Murchison C2 chondrite were examined for organic nitrogen compounds, using mass spectrometry as well as paper and thin-layer chromatography. Under mild extraction conditions (water or formic acid) only aliphatic amines and C₂-C₆ alkylpyridines were seen; the latter may be contaminants. Under drastic extraction conditions (hot, 3–6 M HCl or CF₃COOH), a variety of basic nitrogen compounds appeared, in the following amounts (ppm): adenine (15), guanine (5), melamine (20), cyanuric acid (20–30), guanylurea (30–45), urea (25), etc. Apparently these compounds are present mainly in macromolecular material, and are released only upon acid hydrolysis.These findings support our earlier identifications of these compounds in the Orgueil meteorite. They also suggest that the recent failure by Folsomeet al. (Nature232, 108–109, 1971; Geochim. Cosmochim. Acta37, 455–465, 1973) to find purines or triazines in carbonaceous chondrites was due to inadequate extraction conditions: water and formic acid, rather than HCl. Conversely, we were unable to detect the principal compound class reported by Folsome et al.: 4-hydroxypyrimidines.     

Primordial noble gases in separated meteoritic minerals,II

Eight silicate samples from the Orgueil carbonaceous chrondrite were analyzed for He, Ne, Ar, and Xe by a stepwise heating technique. Six of the samples, including two etched with NaOH, were density fractions covering the following ranges: < 2.35, 2.35–2.45, 2.45–2.48, and > 2.48 g/cm³. Two others were grain-size fractions, separated according to their ability to form a colloid at pH 11.5.All fractions are grossly deficient in cosmogenic neon, having retained only 8–33% of their normal complement. Retentivity increases with density.All fractions give low²⁰Ne/²²Ne ratios above 950°C, suggestive of D.C. Black's exotic “Neon-E” component of²⁰Ne/²²Ne ≤ 3.4. The lowest ratios were found in the low-density and especially the non-colloidal fractions. This suggests that the host phase of Ne-E is a clay mineral of lower iron content and coarser grain size than the main silicates of Orgueil.The main fraction,ρ = 2.35–2.45g/cm³, is inhospitable to Xe; it contains less Xe and releases it more readily at low temperatures (30–35% in 1 hour at 550°C) than do any of the other fractions.     

Salsvatn,a lake with old sea water

Salsvatn is a 464 m deep lake laying 16 m above sea level in North Trøndelag, Norway. The lake was isolated from the sea some 3,000 years ago. It is assumed that salt-water in the deepest 50 m of the lake is the remain of sea water being trapped in the lake at this time. The concentration of cloride in the salt-water layer corresponds to a salinity of 29‰ in ordinary sea water. Hydrography of the lake and changes in some components of the salt water compared with ordinary sea water are discussed. Comparison is made with changes in the stagnant layers of the Black Sea and Lake Rørholtjorden. The latest is another lake with old sea-water at its bottom. Surface sediment samples have been collected from the freshwater and salt-water layers in Lake Rørholtfjorden and from the salt-water layer of Lake Salsvatn. Some chemical components of the sediments and interstitial water have been analysed and discussed.     

Danish seabird disasters in 1972

In recent years the Danish Game Biology Station has studied casualties to seabirds from oil pollution. 1972 was a particularly disastrous year and preliminary information on the events are given here. Very large losses of seabirds have been caused by quite small spillages of oil.     

Luna 20 soil: abundance of 17 trace elements

Luna 20 soil is remarkably similar to Apollo 16 soil, in its content of 17 mainly volatile or siderophile elements: Ag, Au, Bi, Br, Cd, Cs, Ge, In, Ir, Rb, Re, Sb, Se, Te, Tl, U, and Zn. Like other highland soils, it seems to contain an ancient meteoritic component of fractionated, volatile-poor composition. The bulk soil has a high $\text{Tl}\text{Cs}$ ratio (9.4 × 10^?2), similar to that in Apollo 16 soils (5.4 × 10^?2), but higher than that in samples from other sites (1.1 × 10^?2). It is severely contaminated with Ag, Cd, Re, and Sb, judging from a comparison with a 1.7 mg soil breccia sample from the coarse fraction of the soil.     

NOBLE GASES IN THE UNIQUE CHONDRITE,KAKANGARI

The Kakangari chondrite has a cosmic-ray exposure age of 5.4 m.y. and a K-Ar age near 4 g.y. Its high cosmogenic ³He/²¹Ne ratio of 7.5 indicates a small preatmospheric mass. The He and Ne are largely of solar-wind origin, presumably implanted during exposure in the regolith of its parent body. The heavy gases Ar, Kr, Xe are largely of planetary origin. Taken together, the low ¹²⁹Xe/¹³²Xe (1.07), low ³⁶Ar/¹³²Xe (225), and high ¹³²Xe content (45 × 10^?10 cc STP/g) are more similar to the values for unequilibrated ordinary chondrites or even C1, C2 chondrites than to enstatite chondrites, and suggest that Kakangari has the same gas-bearing mineral assemblage as the former, in spite of its high degree of reduction (Fa_4.9).     

Disturbance of beach sediment by off-road vehicles

A three-year investigation was undertaken to examine the effects of off-road vehicles (ORVs) on the beach at Fire Island, New York. Within the National Seashore over 45,000 vehicle trips per year are concentrated in the zone seaward of the dune toe. The experimental approach was adopted in order to assess the environmental effects of ORVs. Specially developed instrumentation was used to measure the direct displacement of sand by vehicles traversing the beach. Direct displacement data were reduced graphically and analyzed by stepwise linear regression. The results of 89 field experiments (788 cases) showed that slope, sand compaction, and number of vehicle passes in the same track were the principal factors controlling the measured net seaward displacement of sand. The data suggest that ORV use levels within the National Seashore could be contributing to the overall erosion rate by delivering large quantities of sand to the swash zone (max. of 119,300 m³/yr). However, with proper management downslope movement of sand could be reduced by an order of magnitude. While vehicular passage over the open beach displaces sand seaward, it is not known if such activity actually increases the amount of erosion, measured as net loss to the beach face.     

Laboratory simulation of meteoritic noble gases. I. Sorption of xenon on carbon: Trapping experiments

We have studied trapping of radioactive ¹²⁷Xe in three types of carbon: carbon black (lamp black  LB), pyrolyzed polyvinylidene chloride (PVDC), and pyrolyzed acridine (C₁₃H₉N). A total of 86 samples were exposed to Xe at T between 100 and 1000°C, for times between 5 min and 240 hours, at p_xe ~ 5 × 10^?7 atm. Excess gas phase and loosely sorbed Xe were pumped away and the remaining, tightly bound Xe was measured by γ-spectrometry.At 100°C,× >90% of the Xe desorbs within a few minutes' pumping but a small amount remains even after 4000 min. Distribution coefficients for this tightly bound Xe are ~1 × 10^?2, 1 and 10 ccSTP/g atm for LB, acridine and PVDC carbons. The tightly bound Xe consists of two components. One occurs over the entire range 100–1000°C, becoming less abundant at high T; it appears to be physisorbed. The other occurs only at T > 500°C and is probably due to volume diffusion. The adsorbed component in LB has an apparent ΔH between ?2.3 and ?5.7 kcal/mole. The diffused component, which occurs in LB and possibly in acridine carbon, has an activation energy Q = 27 ± 8 kcal/mole and a diffusion coefficient D = 1.3 × 10^?17 cm²/sec at 1000°C. These values are comparable to those found for other types of amorphous carbon (Morrisonet al., 1963; Nakai et al., 1960).The low-T component displays two paradoxical features: low ΔH_ads, in the range for Xe physisorbed on carbon, but exceedingly long adsorption or desorption times (~10³ min at 100–400 or 1000°C). Although these long times seem to suggest a high energy process such as chemisorption, our results are best explained by a model that invokes physisorption within a labyrinth of micropores—of atomic dimensions—known to exist in amorphous carbons. The long adsorption/desorption times reflect either the long distances (~5 cm) Xe atoms must migrate by random walk to enter or leave the labyrinth, or the long times needed for Xe atoms to traverse tight spots or constricted pores that connect interior and exterior surfaces of the carbon (activated entry). Both variants of this model predict long equilibration times for the observed ΔH_ads of ?2 to ?6 kcal/mole. Apparently, xenon can be tightly trapped in carbon without resorting to high-energy bonding or to exotic mechanisms.These results suggest that “planetary” type noble gases in meteorites, located at or near grain surfaces of amorphous carbon, may be trapped by adsorption in micropores, whereas components such as CCFXe, which are uniformly distributed in their carrier phases, may be trapped by mechanisms such as volume diffusion or ion implantation.     

Chemical variation in a Proterozoic suite of granitoids extending across a mobile belt — craton boundary

Contrary to earlier opinions, the southwestern margin of the Baltic Shield was formed after the Svecokarelian orogenic event (2.2-1.8 Ga). During the initial stages of its formation (1.7-1.6 Ga), granitoid rocks intruded the southwestern margin and simultaneously also the already cratonized part of the shield. Among these granitoids, the most important chemical difference is between calc-alkalic differentiated granitoids to the west and alkalicalcic more evolved granites to the east of an intraorogenic “suture” (the Mylonite Zone). The chemical differences between alkali-calcic granites found on both sides of the interorogen boundary proper (the Protogine Zone) are less significant. As yet, a final choice cannot be made between wholly actualistic and non-actualistic, possibly intracratonic(?) variants of precursory plate-tectonic processes.