Sulfur earth core

Lewis J. S. (1971) Consequences of presence of sulfur in core of Earth. Earth Planet. Sci. Lett. 11, 130. 

LithophiLes are rock-loving elements found predominantly in oxide minerals or as halides. SiderophUes or iron-loving elements are found mostly in the earths core, and chalcophiles are elements found in the earths crust in combination with nonmetals, including sulfur, selenium, and arsenic. 

The Earth s core is composed of iron-nickel alloy, with an inner solid core surrounded by a molten outer core. A mismatch between the inferred density of the outer core and that predicted for iron-nickel metal at high pressure suggests that some light elements) must dilute the iron in the molten core. Some possibilities are oxygen, sulfur, silicon, and hydrogen, all elements with high cosmic abundances that can alloy with iron at very high... 

As the exploration of the biosphere has continued, environments on Earth have been discovered that are quite different from and alien to human-like life. Nevertheless, where an environment has been found to contain a chemical disequilibrium, if liquid water is also present and the temperature does not exceed the upper limit for covalent bonding of core biomolecules, life is present. Active life has been found in deep-ocean thermal vents at temperatures in excess of 112°C. Life has been found in Antarctica where liquid water exists only transiently. It has been found 5 km below Earth s surface in mine shafts, and in the effluents of mining operations at Rio Tinto, Spain, that are as acidic as dilute sulfuric acid. Several of those environments are summarized in Table 3.1. 

Boness, D. A., and J. M. Brown (1990). The electronic band structure of iron, sulfur and oxygen at high pressure and the earth s core. J. Geophys. Res. 95B, 21721-30. 

Figure 6 Volatile/refractory element ratio-ratio plots for chondrites and the silicate Earth. The correlations for carbonaceous chondrites can be used to define the composition of the Earth, the Rb/Sr ratio of which is well known, because the strontium isotopic composition of the BSE represents the time-integrated Rb/Sr. The BSE inventories of volatile siderophile elements carbon, sulfur, and lead are depleted by more than one order of magnitude because of core formation. The values for Theia are time-integrated compositions, assuming time-integrated Rb/Sr deduced from the strontium isotopic composition of the Moon (Figure 8) can be used to calculate other chemical compositions from the correlations in carbonaceous chondrites (Halliday and Porcelli, 2001). Other data are from Newsom (1995).

Dreibus G. and Palme H. (1996) Cosmochemical constraints on the sulfur content in the Earth s core. Geochim. Cosmochim. Acta 60, 1125-1130. 

The six most abundant, nonvolatile rock-forming elements in the Sun are Si (100), Mg (104), Fe (86), S (43), Al (8.4), and Ca (6.2). The numbers in parentheses are atoms relative to 100 Si atoms. They are derived from element abundances in Cl-meteorites which are identical to those in the Sun except that Cl-abundances are better known (see Chapter 1.03). From geophysical measurements it is known that the Earth s core accounts for 32.5% of the mass of the Earth. Assuming that the core contains only iron, nickel, and sulfur allows us to calculate the composition of the silicate fraction of the Earth by mass balance. This is the composition of the bulk silicate earth (BSE) or the primitive earth mantle (PM). The term primitive implies the composition of the Earth s mantle before crust and after core formation. 

H-chondrite fraction would only be 0.41% based on iridium. This would correspond to 82 ppm S delivered by the late veneer to the mantle. In this case the Earth s mantle should have combined —120 ppm S before the advent of the late veneer. If core formation in the Earth (or in differentiated planetesimals that accreted to form the Earth) occurred while the silicate portion was molten or partially molten, some sulfur must have been retained in this melt (O NeiU, 1991). 

Figure 18 Metallic melt interconnectivity occurs when the dihedral angle between grains becomes <60 . At low pressures, this only occurs at high total anion content (sulfur, carbon, and oxygen). As a result, most metallic liquids relevant to core formation in the Earth and terrestrial planets have dihedral angles > 60°, and thus are unable to connect. In a solid mantle, metallic liquids will be trapped and unable to percolate (after Rushmer et al., 2000 homestead matrix data (2-23 GPa Shannon and Agee (1996) 25 GPa Shannon and Agee (1998))...

FesS at 21 GPa, new eutectic points with lower sulfur contents appear at high pressures (Fei et al, 1997, 2000). Although sulfur is virtually insoluble in solid iron at 1 bar, a limited solid solution between iron and sulfur was observed at 25 GPa (Li et al, 2001). This observation supports sulfur as the principal light element in the outer core. It also indicates that the Earth s inner core may contain a non-negligible amount of sulfur. 

Birch (1952) compared seismically determined density estimates for the mantle and core with the available EOS data for candidate materials. He argued that the inner core was a crystalline phase, mainly iron and the liquid outer core is perhaps some 10-20% less dense than that expected for iron or iron-nickel at core conditions. Later, Birch (1964) showed that the Earth s outer core is —10% less dense than that expected for iron at the appropriate pressures and temperatures and proposed that it contained (in addition to liquid iron and nickel) a lighter alloying element or elements such as carbon, or hydrogen (Birch, 1952) or sulfur, silicon, or oxygen (Birch, 1964). 

There are good reasons to assume that the core contains some amount of carbon, phosphorus, and sulfur. These three elements are among the 12 most common in the Earth that account for >99% of the total mass (Table 5), as based on geochemical, cosmochemical, and meteoritical evidence. Seven out of 12 of these elements (not including carbon, phosphorus, and sulfur) are either refractory or major component elements. 

Figure 8 An illustration showing where S would plot if the core contained 10 wt.% sulfur so to account for the core s density discrepancy (see text for further discussion). The relative abundances of the elements in the Earth are plotted versus the log of the 50% condensation temperature (K) at 10 atm pressure. Data are normalized to Cl carbonaceous chondrite on an equal basis of Mg content. The overall volatility trend for the Earth is comparable to that seen in these chondrites. The shaded region for the carbonaceous chondrites is the same as in Figure 5 (data sources are as in Figure 5).

During the thermally driven differentiation of the Earth into core-mantle-crust, numerous reactions would have produced oxidized forms of iron, sulfur and carbon. These would have contributed to the redox chemistry in the early planet development. Volcanic and hydrothermal emission of sulfur dioxide, SO2, delivered oxidants to the oceans and atmosphere. Photodissociation of water vapor in the atmosphere have undoubtedly provided a small but significant source of molecular oxygen. Furthermore, UV-driven ferrous iron oxidation could have been coupled to the reduction of a variety of reactants, for instance, CO2 (Figure 16). 

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