Pseudo-panspermia

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Pseudo-panspermia (sometimes called soft panspermia, molecular panspermia or quasi-panspermia) is a well-supported hypothesis for a stage in the

origin of life. The theory first asserts that many of the small organic molecules used for life originated in space (for example, being incorporated in the solar nebula, from which the planets condensed). It continues that these organic molecules were distributed to planetary surfaces, where life then emerged on Earth and perhaps on other planets. Pseudo-panspermia differs from the fringe theory of panspermia, which asserts that life arrived on Earth from distant planets.[1]

Background

Further information: Panspermia

Theories of the origin of life have been current since the 5th century BC, when the Greek philosopher

mainstream scientists.[1]

Extraterrestrial creation of organic molecules

Interstellar molecules are formed by chemical reactions within very sparse interstellar or circumstellar clouds of dust and gas. Usually this occurs when a molecule becomes ionised, often as the result of an interaction with cosmic rays. This positively charged molecule then draws in a nearby reactant by electrostatic attraction of the neutral molecule's electrons. Molecules can also be generated by reactions between neutral atoms and molecules, although this process is generally slower.[3] The dust plays a critical role of shielding the molecules from the ionizing effect of ultraviolet radiation emitted by stars.[4] The Murchison meteorite contains the organic molecules uracil and xanthine,[5][6] which must therefore already have been present in the early Solar System, where they could have played a role in the origin of life.[7]

Nitriles, key molecular precursors of the RNA World scenario, are among the most abundant chemical families in the universe and have been found in molecular clouds in the center of the Milky Way, protostars of different masses, meteorites and comets, and also in the atmosphere of Titan, the largest moon of Saturn.[8][9]

Evidence for the extraterrestrial creation of organic molecules includes both their discovery in various contexts in space, and their laboratory synthesis under extraterrestrial conditions:

Extraterrestrial organic molecules found in space
Molecule Class Body Notes
Glycine Amino acid Comet NASA, 2009[10]
mixed
aliphatic
compounds		 Cosmic dust 2011[11][12]
Glycolaldehyde Sugar-related Around a protostar
Copenhagen University, 2012[13][14] Precursor of RNA[15]
Cyanomethanimine, Ethanimine Imines Icy particles in
interstellar space
 Precursors of nucleobase adenine, and of amino acid alanine[16]
polycyclic aromatic hydrocarbons
(PAHs)		 widespread, 20% of carbon in universe NASA, 2014[17]
Glycine,
Methylamine,
Ethylamine		 Amino acid, amines Coma of
67P/Churyumov-Gerasimenko
 Rosetta Mission, 2016[18]
Uracil, Niacin Nucleobase, vitamer 162173 Ryugu Hayabusa2, 2023[19][20]
Laboratory syntheses under extraterrestrial conditions
Molecule Class Conditions Notes
Precursors of amino acids and nucleotides Interstellar medium
polycyclic aromatic hydrocarbons (PAHs)[21][22]
Uracil,
Cytosine,
Thymine		 Nucleobases Pyrimidine, outer space NASA, 2015[23]
Peptides outer space, using CO, C, NH3 Materials common in molecular clouds of interstellar medium[24]

Planetary distribution of organic molecules

Organic molecules can then be distributed to planets including Earth both when the planets formed and later. If the materials from which planets formed contained organic molecules, and were not destroyed by heat or other processes, then these would be available for abiogenesis on those planets.

Later distribution is by means of bodies such as comets and asteroids. These may fall to the planetary surface as meteorites, releasing any molecules they are carrying as they vaporise on impact or later as they erode. Findings of organic molecules in meteorites include:

Organic molecules found in meteorites
Molecule Class Notes
Adenine,
Guanine		 Nucleobase NASA, 2011[25][26]
Sugars In "primitive meteorites"[27]
Guanine,
Adenine,
Cytosine,
Uracil,
Thymine		 Nucleobases 2022[28]


Large Asteroids With Ice And Organic Chemicals
Asteroid Location Notes
24 Themis
Asteroid Belt
Near Earth Objects, life on Earth[29]
269 Justitia
Asteroid Belt
 NASA, JPL Small-Body Database[30]

References

  1. ^
    OCLC 999440041
    . Although they were part of the scientific establishment – Hoyle at Cambridge and Wickramasinghe at the University of Wales – their views on the topic were far from mainstream, and panspermia remains a fringe theory
  2. JSTOR 24913787
    .
  3. PMID 16894166
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  4. ISBN 978-0-7503-0310-1
    .
  5. S2CID 14309508
    .
  6. ^ "We may all be space aliens: study". AFP. 20 August 2009. Archived from the original on June 17, 2008. Retrieved 8 November 2014.
  7. S2CID 14309508
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  8. ISSN 2296-987X
    .
  9. ^ "Building blocks for RNA-based life abound at center of our galaxy". EurekAlert!. 2022-07-08. Retrieved 2022-07-11.
  10. ^ "'Life chemical' detected in comet". NASA. BBC News. 18 August 2009. Retrieved 6 March 2010.
  11. ^ Chow, Denise (26 October 2011). "Discovery: Cosmic Dust Contains Organic Matter from Stars". Space.com. Retrieved 26 October 2011.
  12. S2CID 4419859
    .
  13. ^ Than, Ker (August 29, 2012). "Sugar Found In Space". National Geographic. Archived from the original on September 1, 2012. Retrieved August 31, 2012.
  14. AP News
    . August 29, 2012. Retrieved August 31, 2012.
  15. S2CID 14205612
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  16. S2CID 118522676
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  17. ^ Hoover, Rachel (February 21, 2014). "Need to Track Organic Nano-Particles Across the Universe? NASA's Got an App for That". NASA. Retrieved 22 February 2014.
  18. ^ "Prebiotic chemicals – amino acid and phosphorus – in the coma of comet 67P/Churyumov-Gerasimenko".
  19. ^ Strickland, Ashley (2023-03-21). "RNA compound and vitamin B3 found in samples from near-Earth asteroid". CNN. Retrieved 2023-03-24.
  20. PMID 36944653
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  21. ^ "NASA Cooks Up Icy Organics to Mimic Life's Origins". Space.com. September 20, 2012. Retrieved September 22, 2012.
  22. S2CID 5541727
    .
  23. ^ Marlaire, Ruth (3 March 2015). "NASA Ames Reproduces the Building Blocks of Life in Laboratory". NASA. Retrieved 5 March 2015.
  24. S2CID 246768607
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  25. PMID 21836052
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  26. ^ Steigerwald, John (8 August 2011). "NASA Researchers: DNA Building Blocks Can Be Made in Space". NASA. Retrieved 10 August 2011.
  27. PMID 31740594
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  28. PMID 35473908
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  29. ^ "Life On Earth". NASA-JPL. JPL. Retrieved 14 September 2022.
  30. ^ "NASA Open Data Portal". NASA dot gov. NASA. Retrieved 14 September 2022.
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