Isotope indicators

Helium, as found in nature, consists of two isotopes. Most of the atoms have a mass number 4 but a few have a mass number 3. For each isotope, indicate the ... 

Carboxylic Esters and of Esterification of Carboxylic Acids. Acid Hydrolysis of an Ester with Heavy Oxygen as Isotopic Indicator. J. chem. Soc. [London] 1939, 838. 

Aplin, A. C. and E. A. Warren, 1994, Oxygen isotopic indications of the mechanisms of silica transport and quartz cementation in deeply buried sandstones. 

The specific activity of an isotope indicates the activity per unit mass or volume and is quoted as becquerels per gram (Bq g-1) or millicuries per gram (mCi g-1). A sample in which all the atoms of a particular element are radioactive is said to be carrier-free and is very difficult to achieve in practice. 

Precise measurements of molecules containing more than one rare isotope indicate non-random distributions of the rare isotopes, which potentially may be utilized as one-mineral thermometers. 

The evolution of a large amount (1.12 x 1018 g of CH4) of methane from hydrates is the only plausible hypothesis that has been offered to explain this environmental perturbation. The abnormal 8 l3C isotope indicates that source... 

Fry, B., and R. B. Quinones. 1994. Biomass spectra and stable isotope indicators of trophic level in zooplankton of the northwest Atlantic. Marine Ecology Progress Series 112 201-204. 

The variable isotopic compositions (especially for Pb) reveal geochemi-cally heterogeneous sources. The origin of this heterogeneity is debated and may derive either from shallow mantle processes, such as variable me-tasomatic modifications of the lithosphere by asthenospheric melts, or from mixing between a deep-mantle plume and asthenosphere-lithosphere material. Etna and Ustica show some trace element and isotopic characteristics (e.g. Rb/Nb, Ce/Pb, and boron isotopes), indicative of a contribution from subduction-derived components. 

Kreuzer-Martin, H.W., Ehleringer, J.R., and Hegg, E.L. 2005. Oxygen isotopes indicate most intracellular water in log-phase Escherichia coli is derived from metabolism. Proc. Natl. Acad. Sci. U.S.A. 102 17337-17341. 

From an analytical point of view, we see that an odd molecular mass, based on the predominant isotopes, indicates the presence of an odd number of nitrogen atoms. 

Bird, M. I., W. S. Fyfe, D. Pinheiro-Dick, and A. R. Chivas. 1992. "Carbon isotope indicators of catchment vegetation in the Brazilian Amazon." Global Biogeochemical Cycles 6 293-306. 

Geochemical evidence suggests that there were delays of several hundred million years between the rise of oxygenic photosynthesis, the oxygenation of the atmosphere, and the oxygenation of the deep ocean. Photosynthesis (evidenced by cyanobacterial microfossils and biomarkers) rose as early as 3.5 Ga (billion years before present (Schopf, 1993)) and had been sofidly established by 2.7—2.5 Ga (Brocks et al, 1999 KnoU, 1996 Schopf, 1993 Summons et al, 1999). Data from red beds, detrital mineral deposits, and sulfur isotopes indicate the rise of atmospheric oxygen around 2.4 Ga (Bekker et al, 2004 Chandler, 1980 Des Marais et al, 1992 ... 

The occurrence of hyperfine coupling for a particular isotope indicates non-zero spin density at that nucleus in accordance with the Fermi contact term (which includes the electron wave function evaluated at the nucleus) [1]. The analysis in terms of spin density then requires at least a comparison with the (calculated [5]) isotropic hyperfine splitting constant ao, ideally, results from increasingly available open-shell quantum-chemical calculation procedures [64] are employed. 

The time of core formation on the Earth and Mars can be constrained using chronometers based on short-lived isotopes. The W-Hf isotope system is particularly useful in this respect, consisting of a lithophile parent nucleus, which decays to a siderophile daughter isotope with a half-life of 9 Myr. Recent measurements of an excess of the daughter isotope indicate that the cores of Mars and Earth formed in less than 13 Myr and 30 Myr, respectively (Kleine et al., 2002 Yin et al., 2002 see Chapter 1.20 by Halliday for a more detailed discussion). 

Krabbenhoft D. P., Bullen T. D., and Kendall C. (1992) Isotopic indicators of groundwater flow paths in a northern Wisconsin aquifer. AGU Trans. 73, 191. 

Mariner R. H. and Young H. W. (1996) Lead and strontium isotopes indicate deep thermal-aquifer in Twin Falls, Idaho, area. Feder. Geotherm. Res. Prog. Update 4, 135-140. 

Isotopes Indicate Ancient Life Forms and Climate Changes... 

Figure 2 shows, that in the steady-state situation when pulsing C 0 and Oj sequentially, three types of CO are produced C O, C 0 0, and C O, although only one type, C 0 0, might be expected. The production of the two other CO isotopes indicates that splitting of the C-O bond takes place. This is explained by ... 

It is likely that there is no primitive, undifferentiated mantle still preserved within the Earth s mantle. Nd-isotopes indicate that the mantle experienced a major differentiation event, perhaps as early as 30 Ma after the formation of the solar system, in which a Fe-rich basaltic crust formed on a magma ocean and was... 

Figure 6.52 Mechanistic possibilities for transfer of a monophosphate, (a) 5 1 (P) involving a solvent-equilibrated metaphosphate intermediate. Protonation states are not shown, but different fonts for the phosphorus oxygens, representing different oxygen isotopes, indicate stereochemistry. (b) Canonical structures for metaphosphate and alkyl phosphate dianion, (c) 5n2(P) involving an intermediate which can pseudorotate, (d) Exploded 5Nl(P)-like >Sn2(P) transition states, and cartoon of calculated movements of phosphorus and non-bridge oxygens during phosphoryl transfer through such a transition state, where the leaving to nucleophile atom distance is constant.

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