Simulated meteorite impacts have been observed to produce some organic molecules of interest to abiogenesis researchers. A group of Japanese scientists have designed an experiment to see if meteorite impacts could result in "the building blocks of life."
Their experiments validate a theory first proposed by the American astronomer Carl Sagan in the seventies, says Kakegawa. 'He just mentioned this hypothesis in one sentence in a paper, but he didn't do any experiments. Since then, many people have thought meteorites could produce organic molecules, but we are the first to succeed in showing this.'
Some want meteorites to carry life to Earth, whereas others want them to generate the building blocks of life. (Source here. Ã‚Â©iStockphoto.com/thecarlinco)
The authors simulated chondritic meteorites (thought to be the most primitive) impacting the ocean of the early Earth. To do this they created projectiles and fired them into a substrate to compress and shock solid carbon, iron, nickel, water and nitrogen. They report the production of fatty acids, amines and, when ammonia was added, one amino acid (glycine). They suggest that as impacts were frequent in the early Earth, bombardment led to organic molecules accumulating. This is perceived to be relevant to the origin of life.
The Scientific American report emphasized the tentative nature of the research: meteorites "may have helped spawn life" and "Did heat, pressure and carbon from meteorite impacts create biological precursors?" An astrobiologist is said to fear "that theories of life's origin may never move beyond the hypothetical". Astronomer Donald Brownlee found the research interesting but added: "If the body is too large, generated materials are probably destroyed by impact processes." One of the authors of the paper cautioned that the meteorite-impact theory "is not ready to supplant the vaunted Miller-Urey experiment".
Chemistry World quotes Jeffrey Bada, an expert in prebiotic synthesis at the University of California, San Diego, who doesn't think the results are particularly impressive.
'With the exception of methyl amine and acetic and propanic acid, the yields are very, very small,' he says. 'If glycine is indeed made, the amount that would be present in the ocean from one such impact would be about [10 to the power -30] grams per litre - hardly a meaningful concentration.'
From an ID perspective, the word "supplant" is inappropriate for the Miller-Urey experiments because they cannot carry the burden that people want to place on them. The experiments are a dead-end: there is no route for chemical evolution to proceed. There is a fundamental flaw because of the pre-requisite of a reducing atmosphere (which the meteorite impact experiment avoids), because there is no rationale for chirality to emerge from racemic mixtures, and because no progress has been made in resolving the problem of generating biological information. For more on the problems of building life from chemical precursors, go here and here.
It is worth noting a previous study of impact shocks to produce organic molecules (McKay and Borucki, 1996). These authors confirmed that the elemental conposition of shocked material is important. They based their work on cometary gases: methane, hydrogen cyanide and acetylene. Whilst amine groups were produced, productivity was nil with a carbon dioxide rich mixture. It is possibly significant that carbon dioxide was not mentioned along with nitrogen in the new research.
ID scientists interpret the findings of these abiogenesis scenarios as evidence against life having emerged by this route. It is one thing to generate organic molecules but quite another to label them as "precursors of life". Life does not exist without biological information, and until abiogenesis research takes information seriously, it will continue to explore cul-de-sac avenues.
Biomolecule formation by oceanic impacts on early Earth
Yoshihiro Furukawa, Toshimori Sekine, Masahiro Oba, Takeshi Kakegawa & Hiromoto Nakazawa
Nature Geoscience, 2, 62-66 (January 2009)
Abstract: Intense impacts of extraterrestrial objects melted the embryonic Earth, forming an inorganic body with a carbon-dioxide- and nitrogen-rich atmosphere. Certain simple organic molecules have been shown to form under conditions resembling meteorite impacts, although the link between these events and the development of more complex molecules remains unclear. Ordinary chondrites, the most common type of meteorite, contain solid carbon, iron and nickel - elements essential to the formation of organic chemicals. Here we use shock experiments to recreate the conditions surrounding the impact of chondritic meteorites into an early ocean. We used a propellant gun to create a high-velocity impact into a mixture of solid carbon, iron, nickel, water and nitrogen. After the impact, we recovered numerous organic molecules, including fatty acids, amines and an amino acid. We suggest that organic molecules on the early Earth may have arisen from such impact syntheses. As the natural impacts that were frequent on the early Earth are more sustained and reach higher pressures than our experiments, they may have resulted in the synthesis of a greater abundance, variety and complexity of organic compounds.
Birch, H. Meteorites hitting oceans may have kick-started life, Chemistry World, 08 December 2008
Matson, J. Rock and Roil: Meteorites Hitting Early Earth's Oceans May Have Helped Spawn Life, Scientific American News, 7 December 2008.
McKay, C.P. and W. J. Borucki, W.J., Organic Synthesis in Experimental Impact Shocks, Science, 276, 18 Apr 1996, 390-392.
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