Xenon history

The preservation of distinct mantle reservoirs over time in Mars and the limited degassing experienced by the Martian mantle after the initial period, as indicated by the almost quantitative retention of 244Pu-produced fission xenon, show that Mars has been a static planet with no mantle convection since very early in its history. 

Ozima, M., Podosek, F. A., Igarashi, G. (1985) Terrestrial xenon isotope constraints on the early history of the Earth. Nature, 315, 471 —4. 

The chronology of alteration in CM chondrites is imperfectly understood. Iodine-xenon dating of mineral separates from Murchison, Murray, Mighei, and Cold Bokkeveld (Lewis and Anders, 1975 Niemeyer and Zaikowski, 1980) indicate an extended alteration history for the CMs. Relative to the formation of Murchison magnetite, Murray, and Cold Bokkeveld samples yield closure ages of 10.1 3.2 Myr and at least 11 Myr, respectively, after CAI formation. 

As all known lunar meteorites are finds (and therefore have nonzero terrestrial ages), we need at least four measured quantities to determine the four parameters of a simple one-stage history. Similarly, for a simple two-stage history, we need at least six measured quantities. Typically the data set available comprises He, Ne, Ne, Ar, C1, A1, and e. Occasionally we may have other information— the concentrations of spallo-genic krypton isotopes, spallogenic xenon isotopes, " Ca, and Mn, the densities of nuclear tracks (tracks/unit area), and the concentrations of certain isotopes produced by thermal neutrons, e.g., Ar (from C1) and Gd. 

The model is consistent with the isotopic evidence that upper mantle xenon does not have a simple direct relationship to atmospheric xenon. The radiogenic xenon presently seen in the atmosphere was degassed from the upper portion of the solid Earth prior to the establishment of the present upper mantle steady state xenon isotope compositions and concentrations. The lower mantle ratios are established early in Earth history by decay of I and Pu decay produces a relatively small fraction of fissiogenic nuclides (Porcelli and Wasserburg, 1995b). The xenon daughters (now in the upper mantle) of the shortlived parents are supplied from the lower mantle. The MORE Xe/ Xe ratio (when corrected for air contamination) has no radiogenic contributions... 

There are nine isotopes of xenon (see Table 3). On a global scale, there have been additions to Xe through decay of 1 (fy2 = 15.7 Myr), which as a short-lived nuclide was only present in significant quantities early in Earth history. Additions to the heavy isotopes Xe, Xe, " Xe, and Xe have also occurred by fission of (fi/2 = 80 Myr), another short-lived... 

Contributions to Xe enrichments in MORBs can be from either decay of over Earth history or early " Pu decay, which in theory can be distinguished based on the spectrum of contributions to other xenon isotopes, although analyses have typically not been sufficiently precise to do so. More precise measurements can be obtained... 

Hagee et al., 1990) calculated values of (4-7) X 10 2, with the higher number considered more likely to represent the solar value, although a lower value remains a possibility. The amount produced by U in the bulk silicate Earth (7.5 X 10 2 atoms Xe) is much less, and so bulk silicate Earth (and atmospheric) 2 Xe is dominantly plutonium-derived even if xenon was lost over the first 10 a of Earth history (see Chapter 4.12) so that half of the plutonium-derived xenon was lost, plutonium-derived Xe is still 13 times more abundant in the Earth. 

The depletion of radiogenic xenon in the atmosphere due to losses from the Earth to space must have occurred during early Earth history, when such heavy species could have been lost either from protoplanetary materials or from the growing Earth. Wetherill (1975) proposed that a closure age of the Earth could be calculated by assuming a two-stage history that involved essentially complete loss of 29 Xe and Xe initially, followed by complete closure against further loss. The closure age also can be calculated by combining the and... 

Another constraint on the origin of the xenon now found in the upper mantle is obtained from the composition of fissiogenic Xe. In a closed-system reservoir, plutonium-derived Xe will dominate over uranium-derived Xe (see Section 4.11.3.2). In a system that has been closed throughout solar system history and starting with a chondritic ratio of... 

The atmosphere of Mars has several features that are distinct from that of the Earth and require a somewhat different planetary history. At likely nebular temperatures and pressures at its radial distance. Mars is too small to have condensed a dense early atmosphere from the nebula even in the limiting case of isothermal capture (Hunten, 1979 Pepin, 1991). Therefore, regardless of the plausibility of gravitational capture as a noble-gas source for primary atmospheres on Venus and Earth, some other way is needed to supply Mars. This may include solar-wind implantation or comets. An important feature is that, in contrast to Earth, martian xenon apparently did not evolve from a U-Xe progenitor, but rather from SW-Xe. This requires that accreting SW-Xe-rich materials that account for martian atmospheric xenon are from sources more localized in space or time and so have not dominated the terrestrial-atmospheric xenon budget. There are insufficient data to determineif the martian C/N ratio is like the terrestrial value, but it appears that the initial C/H2O ratio may have been. Further constraints on the sources of the major volatUes are required. 

The solubility of ordinary atmospheric noble gases (neon, argon, krypton, and xenon) in water is temperature dependent (Benson, 1973). The stable isotope composition of precipitation (6 H, 6 0) also depends on ternperamre. If variations in these constituents can be related to a known history of temperature variation, then groundwater residence times can be estimated (Stute and Schlosser, 1993). 

The closed-shell configuration of noble gas atoms Ng does not prevent formation of compounds, either as even, positive oxidation states of xenon, isosteric with iodine complexes (and to a smaller extent by krypton and radon) or functioning as Lewis bases. In condensed matter, Ar, Kr, and Xe form distinct NgCr(CO)j and ArCi(NN)5 complexes. Gaseous noble gas molecular ions, especially HeX and ArX, numerous organo-helium cations, and some neon-containing cations are calculated to be quite stable, and several of them are indeed detected in mass-spectra. The history of Ng chemistry and its relations with the Periodic Table, atomic spectra, and ionization energies, are discussed. 

Where this uniformitarian model is least likely to apply is early in Earth history. The mere existence of the core, separated from the mantle within 30 Myr of Earth formation (Chapters 2.14 and 2.15), along with evidence in atmospheric xenon for the decay products of short-lived I... 

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