Hydrogen early atmosphere

The general possibility of sugar fermentation in the presence of hydrogen sulfide, even in a hydrogen sulfide atmosphere, was recognized at an early date. ... 

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. 

The chemical evolution of the atmosphere can be considered from the thermodynamic standpoint in a broader scheme, including the early stages when the environment was so sharply reducing that free carbon could not yet exist stably. Calculations show that in the presence of liquid water at 25°C a hydrogen-ammonia atmosphere, which is stable when log Pq — 83.0 to — 80.0, is highly reducing (Fig. 22). 

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. 

Although we have discussed the low oxidation state of the early atmosphere and its implications for the form of sulfur in organisms, today this chemistry is largely restricted to anoxic environments. Here sulfur is available as hydrogen sulhde and can be incorporated into amino acids such as cysteine and methionine and then into proteins. The thiolate group RS of cysteine of the thioether of methionine can act as bases or ligands for transition metals such as iron, zinc, molybdenum, and copper. 

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. 

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. 

Urey, Harold Clayton (1893-1981) American chemist who discovered deuterium (heavy hydrogen), the isotope of hydrogen that has a neutron and a proton in the nucleus and is thus twice the weight of common hydrogen, which has only a proton. Urey also worked with Stanley Miller to simulate a primitive atmosphere, thought to be similar to Earth s early atmosphere. Urey was awarded the Nobel Prize in chemistry in 1934. 

Water was surely abundant in early atmospheres and throughout Earth s history with a cooled lithosphere. If there were water. Earth had an oxidizing atmosphere, while hydrogen liberated from water escaped from Earth s atmosphere just as it continues to do today. Both hydrogen gas and helium, when released into Earth s atmosphere, escape from Earth never to return, because the thermal velocity of these gases is above the escape velocity of a mass of their size. They are two of a very few substances that are not automatically recycled. We have no other choice than to recycle unless garbage is to be disposed of in outer space, a highly unlikely event. 

Today, about 21% of Earth s atmosphere is composed of O2, but this was not always the case. Earth s early atmosphere was reducing (rather than oxidizing) and contained hydrogen, methane, ammonia, and carbon dioxide. About 2.7 billion... 

In the early 1920s Badische Arulin- und Soda-Fabrik aimounced the specific catalytic conversion of carbon monoxide and hydrogen at 20—30 MPa (200—300 atm) and 300—400°C to methanol (12,13), a process subsequendy widely industrialized. At the same time Fischer and Tropsch aimounced the Synth in e process (14,15), in which an iron catalyst effects the reaction of carbon monoxide and hydrogen to produce a mixture of alcohols, aldehydes (qv), ketones (qv), and fatty acids at atmospheric pressure. 

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