Earth free oxygen

The biogeochemical processes which control the atmospheric levels of oxygen and carbon dioxide play the most important role in maintaining normal environmental conditions on the Earth. Free oxygen is a prerequisite for existence of major forms of life, and carbon dioxide, being the basic building material for photosynthesis, is also... 

It is also often taken for granted that many of the Earth s subsystems are exposed to free oxygen (O2), leading to a range of one-way reactions of reduced materials (such as organic carbon or metal sulfides) to an oxidized form. As pointed out many times in earlier chapters, the oxidation-reduction status of the planet is the consequence of the dynamic interactions of biogeochemical cycles. As is the case with the acid-base balances, there is considerable sensitivity to perturbations of "redox" conditions, sometimes dramatically as in the case of bodies of water that suddenly become anaerobic because of eutrophication. Another extreme... 

The wavelengths at which most of the components of a primitive Earth atmosphere absorb lie, with few exceptions, under 200 nm. The exceptions include ammonia (< 230 nm), hydrogen sulphide (<260 nm) and ozone (180-300 nm). However, ozone was probably present in the primeval atmosphere only in trace amounts, since free oxygen was only available in extremely low concentrations. The young Earth thus had no protective ozone layer, so short-wavelength UV irradiation could readily penetrate the atmosphere. 

Table III shows the abundance of various elements in the earth s crust and the oxidation states they frequently occupy. The table indicates that of the 14 most abundant elements, only six participate in redox reactions in the surface layers of the earth. [PH3 seems to be extremely rare (42) and will not be discussed.] Because by definition free oxygen as 02 is absent in the anoxic zone, it is evident that oxides of Fe(III) are the most important oxidizers in anoxic environment and that S042 and higher oxides of manganese are of importance only locally. Reducing compounds of importance are organic matter and sulfides, the latter frequently from volcanic emanations. Hydrogen is commonly combined with other elements, as in H20, CH4, and NH3 but may locally occur free as H2. Since iron is the most widespread element that can serve as an oxidizer in the anoxic environment the distribution of the valence states of iron in various rocks is of interest (see Table IV). Sandstones frequently have a high Fe203/Fe0 ratio, but shales and clays may also be highly oxidized as shown in Tables IV and V. Since approximately 75% of the earth s surface is covered with sediments and since the sediments...

Sulphates of the alkali- and alkaline-earth metals are stable at all temperatures lower than that of the electric arc but all other sulphates decompose, the primary product being the oxide of the metal and sulphuric anhydride the latter, however, being unstable at a red-heat, decomposes partly into sulphur dioxide and free oxygen. This decomposition is made use of in the preparation of Nordhausen sulphuric acid, a fuming liquid, consisting chiefly of H2S207 it is made by distilling partially dried ferrous sulphate from fireclay retorts 2 Fe S 04 = Fe2 Oa + S 02 + S 03 the... 

One of the enticing consequences of the excited state dynamics of base pairs is the possible role this property may have played in chemistry on the early earth. Prior to the existence of living organisms photosynthesis would have been absent. Consequently there would have been no free oxygen in the atmosphere and no ozone layer would have existed. The earth s surface would have been exposed to deeper (more energetic) UV irradiation than is the case today. Therefore UV photochemistry is part of the set of rules that may have governed the chemistry that could take place at that time. 

In the case of industrial explosive with a positive -+ Oxygen Balance, the occurrence of free oxygen 02, and in the case of explosive with a very negative oxygen balance, e.g., TNT, the occurrence of elementary carbon C have to be considered. If alkali metal salts such as NaNo3 are included, the carbonates of these are taken as reaction products, e.g., Na2C03. The alkaline earth components, e.g., CaN03 are assumed to form the oxides, e.g., CaO chlorine will be converted into HCI sulfur into S02. 

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