Carbon early atmosphere

D. M. Hunten, Atmospheric evolution of the terrestrial planets. Science 259, 915-920 (1993) J. F. Kasting, Earth s early atmosphere. Science 259, 920-926 (1993) R. A. Berner, Atmospheric carbon dioxide levels over phanerozoic time. Science 249, 1382-1386 (1990) R. A. Berner, Paleozoic atmospheric CO2 importance of solar radiation and plant evolution. Science 261, 68-70 (1993). 

The Earth s early atmosphere provides the carbon dioxide. Several reactions could be the source of the hydrogen. Hydration of the mineral olivine to serpentine releases hydrogen as a by-product, as does the oxidation of methane and gasification of carbon. 

Kasting, J.F. 1990. Bolide impacts and die oxidation state of carbon in the Earth s early atmosphere. Origins Life 20 199-231. See also Schaefer, L., and Fegley Jr., B., 2007, Outgassing of ordinary chondritic material and some of its implications for the chemistry of asteroids, planets, and satellites, Icarus 186.2 462-483. 

It is likely that the use of CO remains from the early atmospheric conditions when life first evolved around 4 billion years ago. This follows from the hypothesis that the first organisms were autotrophic (Huber and Wachtershauser, 1997 Russell et al., 1998). Volcanic gases can contain as high as 1% CO. Early life forms evolving in volcanic sites or hydrothermal vents could have used CO as their carbon and energy source. If this scenario is correct, CO metabolism today can be viewed as the extant survivor of early metabolic processes (Huber and Wachtershauser, 1997). The ability to metabolize CO is still important today since about 10 tons of CO are removed from the lower atmosphere of the earth by bacterial oxidation every year (Bartholomew and Alexander, 1979). This helps to maintain CO below toxic levels, except in extreme cases. 

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

Kasting J. F. (1990) Bolide impacts and the oxidation state of carbon in the Earth s early atmosphere. Origins Life Evol. Biosphere 20, 199-231. 

In contrast, early in the synthesis of the hexahydrobenzofuran portion of the avermectins, Ireland reported that palladium-catalyzed acylation of tetramethyltin was the most effective method for preparing the required methyl ketone as shown in equation (96). The sensitive 3,4-0-isopropylidene-L-threonyl chloride was converted in high yield to the corresponding methyl ketone without epimerization at C-3. To avoid decarbonylation, the reaction was mn under a carbon monoxide atmosphere until completion (4h). 

Kasting, J. F. Ackerman, T. P. 1986. Climatic consequences of very high carbon dioxide levels in the Earth s early atmosphere. Science, 234, 1383-1385. 

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... 

The real values of CO2 content in the early atmosphere are very uncertain. One way to calculate this value is to estimate the crustal abundance of carbon. This element is mainly stored in carbonate rocks and modern assessments give the value of lO" Tg. This is enough to produce an atmospheric pressure of 60 bars if it had been presented as gaseous CO2. Even if only one-third of this amount was present in the atmosphere at the moment of accretion, the pressure would be about 20 bars. How long this dense CO2 atmosphere would have lasted depends on the rate of rock silicate transformation to the carbonates. This rate, in turn, would have depended on the surface temperature on the early Earth and on the amount of continental area exposed to weathering. 

Karhu JA, Holland HD (1996) Carbon isotopes and the rise of atmospheric oxygen. Geology 24 867-870 Kasting JF (1993) Earth s early atmosphere. Science 259 920-926... 

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,... 

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