Water early atmosphere

It has been known for many years [19] that water can be incorporated into silica in the form of hydroxyl groups which have a characteristic absorption in the infrared. This was a problem encountered in the early days of fibre optics communications technology and solved by excluding water from the processing atmospheres. This water can be readily introduced by high temperature annealing in water vapour and removed by heating in a water-free atmosphere. 

In the prebiological early atmosphere, the photolysis of water vapor (H2O) and carbon dioxide (CO2) led to the photochemical production of... 

Once photochemically formed in the early atmosphere via reactions (1), (2), (11), and (12), HhCO, being very water soluble, rained out of the atmosphere. In the early oceans, H2CO accumulated and eventually underwent aqueous solution polymerization reactions leading to the abiotic synthesis of organic molecules of increasing complexity (Pinto et al., 1980). 

This requirement is fulfilled for electric discharges in a reduced atmosphere containing methane, ammonia, and water, as in the original Miller experiment. It has also been observed for atmospheres based on N2 and CO or CO2 on the condition that H2 or methane is also present in snfflcient amonnts (19). A neutral atmosphere (based on N2, CO2, and water) wonld produce much lower yields of organics (by several orders of magnitude). In the absence of other species to be oxidized, the rednction of CO2 reqnires the concomitant thermodynamically nnfavorable conversion of water into O2 (as in photosynthesis). However, even if the atmosphere was nentral when life arose, as nsnaUy believed, the Earth was not nniform with respect to redox state simply becanse the rednced state of the mantle and the high volcanic activity favored the occnrrence of locally rednced environments (for instance, in hydrothermal vents in the oceans). Then, a preservation of the hydrogen content of the early atmosphere or the diversity of environments on the early Earth is likely to have made amino acid formation possible, at least at specific places. 

Possibly the earliest habitats were thin biofilms of bacteria and archaea that existed by processing redox contrast between hydrothermal products and the external environment (sea water and atmosphere). The productivity of these early microbial mats would have been severely limited by the inorganic sources of redox power from below. Volcanic and hydro-thermal processes would have ensured a small but steady supply of H2, H2S, CH4 and possibly HCN from below. Nitrate (from dissolved NO2), and sulphate are crucial. Some sulphate would have come from dissolved magmatically exhaled SO3. Some would have been supplied by disproportionation of sulphite in seawater, the sulphite having come from magmatic SO2. Some sulphate would have been made photo-chemically in air. 

Box 2. The Content of CO2 in the Prebiotic Atmosphere, after Fenchel et al, 1998 Perhaps the most interesting question on the early atmosphere is related to the abundance and oxidation states of carbon. Current models predict a CO2-rich atmosphere, which would contain a trace amount of methane and a slightly greater amount of carbon monoxide. We can try to explain it on the basis of the following speculations. It is known that even today volcanic activity is a dominant process in releasing CO2 and it should have been so in the past. It is related to the reasonable suggestion that the oxidation state of the upper mantle was about the same as today. Furthermore, the by-products of water vapor photolysis were enabled to oxidize both CH4 and CO. The possible reaction pathway could be the following... 

It is generally believed that the solar system condensed out of an interstellar cloud of gas and dust, referred to as the primordial solar nebula, about 4.6 billion years ago. The atmospheres of the Earth and the other terrestrial planets, Venus and Mars, are thought to have formed as a result of the release of trapped volatile compounds from the planet itself. The early atmosphere of the Earth is believed to have been a mixture of carbon dioxide (C02), nitrogen (N2), and water vapor (H20), with trace amounts of hydrogen (H2), a mixture similar to that emitted by present-day volcanoes. 

The composition of the present atmosphere bears little resemblance to the composition of the early atmosphere. Most of the water vapor that outgassed from the Earth s interior condensed out of the atmosphere to form the oceans. The predominance of the C02 that outgassed formed sedimentary carbonate rocks after dissolution in the ocean. It is estimated that for each molecule of C02 presently in the atmosphere, there are about 105 C02 molecules incorporated as carbonates in sedimentary rocks. Since N2 is chemically inert, non-water-soluble, and noncondensable, most of the outgassed N2 accumulated in the atmosphere over geologic time to become the atmosphere s most abundant constituent. 

It is generally agreed that the early atmosphere was a reducing one and most likely consisted of water, methane, carbon dioxide, and nitrogen,... 

Summarizing the data of these works it can be concluded that ettringite is stable in low presstrre steam ctrring even at temperature of 90 °C. However, the autoclaving of paste leads to decomposition of ettringite as early as at temperature of 110 °C. In this condition the c monosrrlphate is stable in these conditiorrs because it decomposes, in the satrrrated water vapour atmosphere at the temperatrrre of 190 °C [98]. 

Water (H2O), ammonia (NHj), methane (CH ), and nitrogen (N2) are present in the early atmosphere. The supply of cyan gas (CNjj, hydrogen cyanide (HCN), carbon monoxide (CO), and hydrogen (Hj) is also adequate. Amino acids and lipids are formed in large amounts. Subsequently, proteins are formed from amino acids and colloidal systans from lipids. Vesicles bounded by phospholipid bilayers turn out to be strong and reproducible. 

In the early twenty-first century, the population of the world edged toward 7 billion, increasing the amount of pollution that reaches the land, water, and atmosphere. Many natural ecosystems are struggling to cope with the remnants of old toxic contamination and the influx of new contamination. The ecological, social, and economic costs of pollution are immeasurable, and environmental recovery is one of the most important problems facing the global community. 

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