10:45 AM - 12:15 PM
[MIS03-P01] Evaluation of the effects of solar-energy particles on amino acid production in early Earth atmosphere
Keywords:Amino acid, Solar Energetic Particles , Primitive earth
Before life began, bioorganic compounds such as amino acids must have formed on Earth.Since Miller's experiment [1], many experiments have been conducted by using strongly reducing gas mixtures, which simulated the environment of the primitive earth, and it has been reported that amino acids were produced by various energies in such an environment [2]. In recent years, however, it was believed that the primitive Earth's atmosphere was not as a strongly reducing atmosphere as used in Miller's experiment, but a slightly reducing atmosphere [3], which made it difficult to produce amino acids with conventionally-considered energies [4, 5]. It was shown, however, if the primitive Earth atmosphere contained CO, amino acids could be produced by cosmic rays [6, 7]. Although it is not clear how much CO was contained, we can assume that the primitive Earth's atmosphere was slightly reducing [3].
It was suggested that that the young Sun had huge and frequent flares, which would have shot out high flux of solar energetic particles (SEPs) [8, 9]. Such high-energy particles would have caused chemical reactions in planetary atmospheres. In the present study, we examined possible formation of organic compounds from slightly reducing gas mixture, mainly composed of N2, CO2 and H2O with CO as a minor component.
A gas mixture (700 Torr) and pure water (5 mL) was put in a 400 mL Pyrex tube with a Havar foil window, and the gas mixture was irradiated with 2.5 MeV protons (2.0 mC) from a Tandem accelerator (Tokyo Institute of Technology). The gas mixtures used were (i) CO2and N2 (molar ratio 1:1) (ii) CO2, CO and N2 (molar ratio 9:1:10). The similar gas mixture was put in a 400 mL Pyrex tube with a quartz window, and then was irradiated with UV light from a 450 W Xe lamp (Hamamatsu Photonics) for 4 hours. In some experiments, 13CO was used in place of CO.
The resulting gaseous products were analyzed by GC/MS (Shimadzu GCMS-QP2020: column: Poraplot Q). The aqueous products were acid hydrolyzed before amino acid analysis. Amino acids were determined by ion-exchange HPLC (Shimadzu LC-10AT) after acid-hydrolysis, where post-column derivatization with o-phthalaldehyde and N-acetyl-L-cysteine was applied. Amino acids were also determined by GC/MS (Shimadzu GCMS-QP2020: column: CP-Chirasil L-Val) after derivatization with hexafluorobutanol and ethyl chloroformate.
When a mixture of CO2, N2 and H2O was irradiated with protons, only trace level of amino acids were detected, but CO and N2O were detected in gas phase products. N2O is far more effective greenhouse gas than CH4 and CO2, so that it might solve the faint young sun paradox [10]. After proton irradiation of a mixture of CO2, CO, N2 and H2O, 1.6 mmol of glycine and several other amino acids were detected in the aqueous product. Indigenousness of the amino acids was confirmed by the proton irradiation of a mixture of CO2, 13CO, N2and H2O: Amino acids labelled with 13C atom were detected by GC/MS. The G-value of glycine here is 0.044. We assume the SEPs energy flux as 3 × 1024 eV m-2 yr-1 [11]. The annual glycine production rate estimated by using these values was 8.4 ×109 kg yr-1, which is much larger than the amount of glycine delivered by meteorites [12]. On the other hand, no amino acids were detected in the present UV irradiation experiments.
It was suggested that SEPs was an effective energy source for the formation of bioorganic compounds including amino acids from slightly reducing atmospheres. Further studies to examine possible roles of SEPs in prebiotic synthesis is in progress. We are planning to characterize amino acid precursors, which are the forms of amino acids before they are isolated.
[1] Miller, S. L., Science 117, 528 (1953)
[2] Miller, S. L. and Orgel, L. E., The Origins of Life on the Earth, Prentice-Hall, Englewood Cliff (1974).
[3] Catling, D. C.; Casting, J. F. Atmospheric Evolution on Inhabited and Lifeless Worlds, Cambridge University Press, Cambridge, UK, 2017.
[4] Schlesinger, G and Miller, S. L., J. Mol. Evol. 19, 376 (1983).
[5] Kuwahara, H. et al., Orig. Life Evol. Biosph. 42, 533 (2012).
[6] Kobayashi, K. et al., Orig. Life Evol. Biosph. 28, 155 (1998).
[7] Miyakawa, S. et al., Proc. Natl. Acad. Sci. USA, 28, 14628 (2002).
[8] Maehara, H. et al. (2012) Nature 485, 478.
[9] Airapetian, V. S. et al. Nat. Geosci. 9, 452 (2016).
[10] Sagan, C. and Mullen, G. (1972) Science, 177, 52 (1972).
[11] Kobayashi, K. et al., Life, submitted.
It was suggested that that the young Sun had huge and frequent flares, which would have shot out high flux of solar energetic particles (SEPs) [8, 9]. Such high-energy particles would have caused chemical reactions in planetary atmospheres. In the present study, we examined possible formation of organic compounds from slightly reducing gas mixture, mainly composed of N2, CO2 and H2O with CO as a minor component.
A gas mixture (700 Torr) and pure water (5 mL) was put in a 400 mL Pyrex tube with a Havar foil window, and the gas mixture was irradiated with 2.5 MeV protons (2.0 mC) from a Tandem accelerator (Tokyo Institute of Technology). The gas mixtures used were (i) CO2and N2 (molar ratio 1:1) (ii) CO2, CO and N2 (molar ratio 9:1:10). The similar gas mixture was put in a 400 mL Pyrex tube with a quartz window, and then was irradiated with UV light from a 450 W Xe lamp (Hamamatsu Photonics) for 4 hours. In some experiments, 13CO was used in place of CO.
The resulting gaseous products were analyzed by GC/MS (Shimadzu GCMS-QP2020: column: Poraplot Q). The aqueous products were acid hydrolyzed before amino acid analysis. Amino acids were determined by ion-exchange HPLC (Shimadzu LC-10AT) after acid-hydrolysis, where post-column derivatization with o-phthalaldehyde and N-acetyl-L-cysteine was applied. Amino acids were also determined by GC/MS (Shimadzu GCMS-QP2020: column: CP-Chirasil L-Val) after derivatization with hexafluorobutanol and ethyl chloroformate.
When a mixture of CO2, N2 and H2O was irradiated with protons, only trace level of amino acids were detected, but CO and N2O were detected in gas phase products. N2O is far more effective greenhouse gas than CH4 and CO2, so that it might solve the faint young sun paradox [10]. After proton irradiation of a mixture of CO2, CO, N2 and H2O, 1.6 mmol of glycine and several other amino acids were detected in the aqueous product. Indigenousness of the amino acids was confirmed by the proton irradiation of a mixture of CO2, 13CO, N2and H2O: Amino acids labelled with 13C atom were detected by GC/MS. The G-value of glycine here is 0.044. We assume the SEPs energy flux as 3 × 1024 eV m-2 yr-1 [11]. The annual glycine production rate estimated by using these values was 8.4 ×109 kg yr-1, which is much larger than the amount of glycine delivered by meteorites [12]. On the other hand, no amino acids were detected in the present UV irradiation experiments.
It was suggested that SEPs was an effective energy source for the formation of bioorganic compounds including amino acids from slightly reducing atmospheres. Further studies to examine possible roles of SEPs in prebiotic synthesis is in progress. We are planning to characterize amino acid precursors, which are the forms of amino acids before they are isolated.
[1] Miller, S. L., Science 117, 528 (1953)
[2] Miller, S. L. and Orgel, L. E., The Origins of Life on the Earth, Prentice-Hall, Englewood Cliff (1974).
[3] Catling, D. C.; Casting, J. F. Atmospheric Evolution on Inhabited and Lifeless Worlds, Cambridge University Press, Cambridge, UK, 2017.
[4] Schlesinger, G and Miller, S. L., J. Mol. Evol. 19, 376 (1983).
[5] Kuwahara, H. et al., Orig. Life Evol. Biosph. 42, 533 (2012).
[6] Kobayashi, K. et al., Orig. Life Evol. Biosph. 28, 155 (1998).
[7] Miyakawa, S. et al., Proc. Natl. Acad. Sci. USA, 28, 14628 (2002).
[8] Maehara, H. et al. (2012) Nature 485, 478.
[9] Airapetian, V. S. et al. Nat. Geosci. 9, 452 (2016).
[10] Sagan, C. and Mullen, G. (1972) Science, 177, 52 (1972).
[11] Kobayashi, K. et al., Life, submitted.