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Earth's early atmosphere

Earth's early atmosphere. Old models : Oparin's assumption (1938) : organic compounds have been produced under reducing conditions.

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Earth's early atmosphere

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  1. Earth's early atmosphere Old models : • Oparin's assumption (1938) : organic compounds have been produced under reducing conditions. • Miller & Urey (1959) : "It would not have been possible to synthesize organic compounds non-biologically as long as oxidizing conditions were present on the earth."

  2. Earth formed relatively slowly. • Highly reduced volcanic gases were released. • Urey (1952) : The hydrogen must escape in order for an oxidized to be established.

  3. Recent models : • Earth formed in 10 - 100 million years. • Earth's core and accretion were formed simultaneously. • Volcanic gases were oxidized - 4.5 billion years ago (Ga).

  4. A key question : How H2CO, HCN could have formed in a reducing atmosphere?

  5. The primitive atmosphere :Reducing or Oxidizing ?

  6. Final conclusion : If there is enough time, a variety of organic compounds will be synthesized in both conditions.

  7. Could organic synthesis occur undersimulated prebiotic environment ? A short historical review • 1953 – Miller : a production of amino acids under possible primitive earth conditions. • 1961 – Oro : synthesis of Adenine from Hydrogen Cyanide under possible primitive earth conditions. • 1980 – Pinto, GladsStone & Yung : photochemical production of Formaldehyde in earth’s primitive atmosphere.

  8. A production of amino acids under possible primitive earth conditions [S.L.Miller, Science, 117, 528 - 9 (1953)] Experiment’s aim : testing the hypothesis that the organic compounds that serve as the basis of life were formed when the earth had an atmosphere of : Methane (CH4) Ammonia (NH3) Water (H2O) Hydrogen (H2)

  9. Procedure : • An apparatus was built to circulate CH4, NH3, H2O and H2 past an electric discharge. • The resulting mixture has been tested for amino acids by Paper Chromatography.

  10. Gases : CH4 NH3 H2 Induction coil Boiling water

  11. Results : 1. The solution became red and turbid. 2. Certain identification of Glycine,  – Alanine,  – Alanine. 3. Identification of Aspartic acid,– Amino – n – Butyric acid.

  12. Conclusion : There could be a production of Amino acids under primitive earth conditions.

  13. Criticism : CH4, NH3 may not have been present in the atmosphere of early earth.

  14. Mechanism of synthesis ofAdeninefrom Hydrogen Cyanide under possible primitive earth conditions [J.Oro, Nature, 191, 1193-4 (1961)] Starting point : Adenine is formed spontaneously from Hydrogen Cyanide in Water – Ammonia systems under conditions assumed to have existed on the primitive earth.

  15. What’s new ? • Adenine formation from Hydrogen Cyanide is thought to be initiated by base catalysis (NH3) and to require the participation of 4 – Aminoimidazole – 5 Carboxamidine and Formamidine as the key intermediates. • Oro gives the mechanism of the Formation of Adenine from Hydrogen Cyanide.

  16. Photochemical production of Formaldehydein earth's primitive atmosphere. [J, P. Pinto et al, Science, 210, 183-5 (1980)] • Formaldehyde (H2CO) - A key role in synthesis of complex organic molecules on the primitive earth. • Starting point : earth's primitive reducing atmosphere (includes : H2O, CO2, N2 + traces of H2, CO).

  17. The production of H2CO from CO2 is described by the following reaction sequence :

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