Earth volatile elements

Figure 4 shows vapor pressure curves of rare-earth metals[24], clearly showing that there is a wide gap between Tm and Dy in the vapor pressure-temperature curves and that the rare-earth elements are classified into two groups according to their volatility (viz.. Sc, Y, La, Ce, Pr, Nd, Gd, Tb, Dy, Ho, Er, and Lu, non-volatile elements, and Sm, Eu, Tm, and Yb, volatile elements). Good correlation between the volatility and the encapsulation of metals was recently... 

Of the two models, homogeneous accretion is generally favoured. H. Wancke from the Max Planck Institute in Mainz (1986) described a variant of this model, in which the terrestrial planets were formed from two different components. Component A was highly reduced, containing elements with metallic character (such as Fe, Co, Ni, W) but poor in volatile and partially volatile elements. Component B was completely oxidized and contained elements with metallic character as their oxides, as well as a relatively high proportion of volatile elements and water. For the Earth, the ratio A B is calculated to be 85 15, while for Mars it is 60 40. According to this model, component B (and thus water) only arrived on Earth towards the end of the accretion phase, i.e., after the formation of the core. This means that only some of the water was able to react with the metallic fraction. 

Copper in meteorites is depleted in the heavier 65 isotope with respeet to the Earth (Luek et al. 2003 Russell et al. 2003). Luck et al. s (2003) study of the four main groups of carbonaceous chondrites CI-CM-CO-CV showed that Cu depletion is maximum (-1.5%o) for the C V chondrites (e.g., Allende) for which the depletion of volatile elements is strongest, which indicates that volatilization does not accormt for the observed isotopic heterogeneity (Fig. 4). Luck et al. (2003) found that 8 Cu in CI-CM-CO classes correlates with O excess, but this does not seems to be the case for CV (Luck et al. 2003) nor for the CR, CB, and the particularly Cu-depleted CH-like classes (Russell et al. 2003). In contrast, chondritic Zn is relatively heavy with 8 Zn up to 1 %o (Luck et al. 2001). The rather high 5 Zn values of iron meteorites (up to 4%o)is reminiscent of a similar fractionation of Fe isotopes between metal and silicates (Zhu et al. 2002). 

Wai, . M. and Wasson, J. T. (1977) Nebular condensation of moderately volatile elements and their abundances in ordinary chondrites. Earth and Planetary Science Letters, 36, 1-13. 

Trace element measurements in lunar basalts also indicate that the Moon is depleted in highly volatile elements (Taylor et al., 2006a). Estimates of some of the Moon s volatile element concentrations are compared with the Earth in Figure 13.11 a. The absence of water in lunar basalts suggests that the mantle is dry. The Moon may also be enriched in refractory elements (Fig. 13.11b). Volatile element depletion and refractory element enrichment are expected consequences of the giant impact origin and subsequent high-temperature accretion of the Moon. 

Mars bulk silicate (mantle + crust) composition, estimated from Martian meteorites by Wanke and Dreibus (1988). This composition differs from the bulk silicate of Earth, because of differences in volatile element abundances and core differentiation. 

As the Celestial Fire begins to coagulate or condense, it forms "an invisible most subtle humidity" as the Element Air. This process of inspissation or thickening continues and the Air condenses into the Water Element, then Water condenses into the Earth Element. The Fire trapped within (the Central Fire) now reflects and drives this process in reverse. The Earth volatilizes and becomes a thickened Water. The Water volatilizes and becomes vaporous, and the Air becomes ratified into the Fire Element where it is regenerated by the Celestial Fire and the cycle begins anew. 

Laboratory study of the first lunar samples brought to Earth by Apollo 11 ruled out all ideas that the Moon might be a primitive object, i.e. an object that had remained rather cool after its accumulation with only minor melting processes induced by large impacts on the surface. On the contrary, it became evident from the chemical analysis that the Moon, like the Earth, is a highly differentiated object. On the Moon many chemical elements are strongly enriched or depleted as compared with their abundances in carbonaceous chondrites which apart from the most volatile elements, are believed to be most representative of solar matter. Thus it became clear that, at least in the upper 200 km, extensive melting processes must have occurred. 

The siderophile elements (Ir, Au, Re, Ni, etc.) seem to be the most reliable indicators of meteoritic material. These elements concentrate in the metal phase during the planetary melting and are therefore strongly depleted in the surface layers of differentiated planets (e.g. on Earth by a factor of 10-4). However, a number of volatile elements (Ag, Bi, Br, Cd, Ge, Pb, Se, Te, Zn) are so strongly depleted on the lunar surface that some of them can serve as subsidiary indicators of meteoritic matter. 

In the beginning of the nineteenth century, analytics of plant matter samples started with that of plant ashes. In addition, no methods were available then which could have enabled intact biological materials to be digested for complete, no-Ioss analyses without burning them before. Hence, volatile elements then could not be detected, let alone quantified in biomass. Elements then found in plant ashes (Fe, Na, K, Ca, etc.) were both abundant and had been discovered in other sources before. As, e.g., no spectroscopic methods whatsoever were at hand earlier than about 1860, technical prospects for trace analysis then were dim at best (there are very few instances of elements detected in environmental samples/spectra prior to their isolation on Earth helium (in 1868) and techne-tinm (in 1952) were found in stellar spectra before being isolated from or detected in terrestrial minerals... 

It was during the same time that astronomers began to extract quantitative information about elemental abundances in the Sun by solar absorption spectroscopy and it was soon realized that the compositions of the Sun and the whole Earth are similar, except for hydrogen and other extremely volatile elements (see Russell, 1941). 

These particles probably come from the asteroid belt (Elynn, 1994). They are brought to Earth by the action of the Poynting-Robertson effect. Perhaps they are derived from sources that contain uncondensed volatiles from the inner part of the nebula. This would be the only example of a clear enhancement of moderately volatile elements in solar system material. 

Most meteorites are depleted in moderately volatile and highly volatile elements (see Figures 2-4). The terrestrial planets Earth, Moon, Mars, and the asteroid Vesta show similar or even stronger depletions (e.g., Palme et aL, 1988 Palme, 2001). The depletion patterns in meteorites and in the inner planets are qualitatively similar to those in the ISM. It is thus possible that the material in the inner solar system inherited the depletions from the ISM by the preferential accretion of dust grains and the loss of gas during the collapse of the molecular cloud that led to the formation of the solar system. There is, however, little support for this hypothesis ... 

Comets are rich in volatile elements, but they probably delivered no more than 10% of Earth s volatile inventory. There are several reasons for this. Comets have a very low impact probability with Earth over their dynamical lifetime ( 10 Levison et al., 2000), limiting the amount of cometary material that Earth could have accreted. In addition, if most of Earth s water was acquired from comets, it seems likely that Earth s noble gas abundances would be higher than observed by several orders of magnitude (Zahnle, 1998). Einally, water measured spectroscopically in comets differs isotopically from that of seawater on Earth, with the cometary D/H ratio being greater by a factor of 2 (Lunine et al., 2000). 

Nebular Gases and Earth-like versus Jupiter-like Planets Depletion in Moderately Volatile Elements Solar Mass Stars and Heating of the Inner Disk The Hot Nebula" Model... 

Not only is there a shortage of nebular gas in the Earth and terrestrial planets today but the moderately volatile elements also are depleted (Figure 1) (Gast, 1960 Wasserburg et al, 1964 Cassen, 1996). As can be seen from Figure 2, the depletion in the moderately volatile alkali elements, potassium and rubidium in particular, is far greater than that found in any class of chondritic meteorites (Taylor and Norman, 1990 Humayun and Clayton, 1995 Halliday and Porcelli, 2001 Drake and Righter, 2002). The traditional explanation is that the inner terrestrial planets accreted where it was hotter. 

---