Origin of Life

Theories and evidence for chemical biopoieses

Primordial Atmosphere.

A hydrogen-rich early Earth atmosphere. : "We show that the escape of hydrogen from early Earth's atmosphere likely occurred at rates slower by two orders of magnitude than previously thought. The balance between slow hydrogen escape and volcanic outgassing could have maintained a hydrogen mixing ratio of more than 30%. The production of prebiotic organic compounds in such an atmosphere would have been more efficient than either exogenous delivery or synthesis in hydrothermal systems. The organic soup in the oceans and ponds on early Earth would have been a more favorable place for the origin of life than previously thought."

Tian F, Toon OB, Pavlov AA, De Sterck H. A hydrogen-rich early Earth atmosphere. Science. 2005 May 13;308(5724):1014-7. Epub 2005 Apr 7. Comment in: Science. 2005 May 13;308(5724):962-3.

The evolution of the prebiotic atmosphere : "High CO2 levels are required to warm the primitive earth in the face of decreased solar luminosity. The atmosphere should have had an effective stratospheric cold trap, which would have limited the abiotic production rate of oxygen to relatively low values. Photostimulated oxidation of ferrous iron in the oceans should have been the dominant source of atmospheric H2. Rainout of H2O2 would have kept the atmospheric H2 content high and the O2 content low, even if other sources of H2 were small."
Article / PubMed / ChemPort
Kasting, J.E. The evolution of the prebiotic atmosphere. Origins of Life 14, 75−82 (1984).

Nitrogen fixation by corona discharge on the early precambrian Earth. : Entrez PubMed: "We report the first experimental study of nitrogen fixation by corona discharge on the anoxic primitive Earth. The energy yields of nitric oxide (NO) and nitrous oxide (N(2)O) were experimentally determined over a wide range of CO(2)-N(2) mixtures simulating the evolution of the Earth's atmosphere during the Hadean and Archean eras (from 4.5 ba to 2.5 ba). NO, the principal form of fixed nitrogen in lightning and coronal discharge in early Earth, is produced ten times less efficiently in the latter type of electrical discharge with an estimated maximum annual production rate of the order of 10(10) g yr(-1). For N(2)O the maximum production rate was estimated to be approximately 10(9) g yr(-1). These low rates of syntheses indicate that corona discharges as point discharges on the clouds and ground did not play a significant role in the overall pool of reactive nitrogen needed for the emergence and sustainability of life."

Nna-Mvondo D, Navarro-Gonzalez R, Raulin F, Coll P. Nitrogen fixation by corona discharge on the early precambrian Earth. Orig Life Evol Biosph. 2005 Oct;35(5):401-9.

Neon isotopes constrain convection and volatile origin in the Earth's mantle.: "Identifying the origin of primordial volatiles in the Earth's mantle provides a critical test between models that advocate magma-ocean equilibration with an early massive solar-nebula atmosphere and those that require subduction of volatiles implanted in late accreting material. Here we show that neon isotopes in the convecting mantle, resolved in magmatic CO2 well gases, are consistent with a volatile source related to solar corpuscular irradiation of accreting material. This contrasts with recent results that indicated a solar-nebula origin for neon in mantle plume material, which is thought to be sampling the deep mantle. Neon isotope heterogeneity in different mantle sources suggests that models in which the plume source supplies the convecting mantle with its volatile inventory require revision. Although higher than accepted noble gas concentrations in the convecting mantle may reduce the need for a deep mantle volatile flux, any such flux must be dominated by the neon (and helium) isotopic signature of late accreting material."Ballentine CJ, Marty B, Sherwood Lollar B, Cassidy M. Neon isotopes constrain convection and volatile origin in the Earth's mantle. Nature. 2005 Jan 6;433(7021):33-8. Comment in: Nature. 2005 Jan 6;433(7021):25-6.

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Efficient near ultraviolet light induced formation of hydrogen by ferrous hydroxide.

Entrez PubMed: "The formation of hydrogen on irradiating ferrous ion in aqueous solution or suspension was studied over a wide range of pH. In addition to the known reaction in acid solution which decreases in yield with increasing pH and required far UV light, there is an efficient reaction occurring between pH 6 and 9 which utilizes near UV light. The latter reaction is an approximately linear function of both the concentration of ferrous ion and the light intensity. The quantum yield of hydrogen from the suspension of Fe(OH)2 at pH 7.2 is very high: > or = 0.3. The quantum yield decreases by a factor of five at 1 mole percent of ferric ions. To explain these observations it is proposed that an intermediate formed on excitation of the Fe(OH)2 polymer is further reduced by a neighboring Fe(+2) to form H2. These results support the work of Braterman et al. (1983) which claimed that the near UV driven photooxidation of ferrous ions could be responsible for formation of the Banded Iron Formations on the early earth. The efficient photoreaction observed in the present work could also serve as a source of active reducing equivalents to reduce CO2 and thus provide a solution to a dilemma in the arguments on the role of reduced carbon in the origin of life."
Borowska ZK, Mauzerall DC. Efficient near ultraviolet light induced formation of hydrogen by ferrous hydroxide. Orig Life Evol Biosph. 1987;17:251-9.

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Early Earth Atmosphere Hydrogen-rich, Favorable To Life

U. Of Colorado Study Shows Early Earth Atmosphere Hydrogen-rich, Favorable To Life: "Published in the April 7 issue of Science Express, the online edition of Science Magazine, the study concludes traditional models estimating hydrogen escape from Earth's atmosphere several billions of years ago are flawed. The new study indicates up to 40 percent of the early atmosphere was hydrogen, implying a more favorable climate for the production of pre-biotic organic compounds like amino acids, and ultimately, life.

Toon said the premise that early Earth had a CO2-dominated atmosphere long after its formation has caused many scientists to look for clues to the origin of life in hydrothermal vents in the sea, fresh-water hot springs or those delivered to Earth from space via meteorites or dust.

The new study indicates the escape of hydrogen from Earth's early atmosphere was probably two orders of magnitude slower than scientists previously believed, said Tian. The lower escape rate is based in part on the new estimates for past temperatures in the highest reaches of Earth's atmosphere some 5,000 miles in altitude where it meets the space environment.

While previous calculations assumed Earth's temperature at the top of the atmosphere to be well over 1,500 degrees F several billion years ago, the new mathematical models show temperatures would have been twice as cool back then. The new calculations involve supersonic flows of gas escaping from Earth's upper atmosphere as a planetary wind, according to the study.

Despite somewhat higher ultraviolet radiation levels from the sun in Earth's infancy, the escape rate of hydrogen would have remained low, Tian said. The escaping hydrogen would have been balanced by hydrogen being vented by Earth's volcanoes several billion years ago, making it a major component of the atmosphere."

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