Sunday, November 27, 2011

NASA Confusion About the Origin of Life

NASA-funded researchers have evidence that some building blocks of DNA, the molecule that carries the genetic instructions for life, found in meteorites were likely created in space. The research gives support to the theory that a "kit" of ready-made parts created in space and delivered to Earth by meteorite and comet impacts assisted the origin of life. [NASA Researchers: DNA Building Blocks Can Be Made in Space]

Most scientists are not thinking critically about the origin of life. It is extremely improbable that asteroids could have delivered enough amino acids or purines to make a difference. Given the known stability of these molecules in the ocean, you would have to achieve an enormous delivery rate to make a concentration sufficient to drive polymerization. It's much more likely that the first complex amino acids, and the first purines and pyrimidines, were synthesized in special environments on Earth using simple inorganic precursors. This is the origin of life scenario promoted as "Metabolism First" [More Prebiotic Soup Nonsense].

I wish NASA astrobiologists would stop making the assumption that all they have to do is discover complex organic molecules in asteroids in order to solve the origin of life. There are a lot of steps between finding purines in asteroids and making a prebiotic soup that could contribute to the origin of life. Those steps need to be spelled out in their press releases so the public can evaluate the discovery.

Here's what I wrote a few years ago .... [Can watery asteroids explain why life is 'left-handed'?]
In order for extraterrestrial organic matter to have fueled the origin of life, a lot of meteorites carrying organic matter had to arrive on the primitive Earth. The problem of amino acid concentrations and stabiltity were discussed in a classic paper by Jeffrey Bada published in 1991.

Some of his calculations are worth remembering.

The current flux of extraterrestrial organic material is about 3 × 108 grams per year from cosmic dust and micrometeorites. About 1% of this is amino acids and most of them are not the ones found in living organisms. This should give rise over time to a concentration in the oceans of about 0.1 nM (10-10 M). That's not sufficient for life to have originated.

The flux in the past was almost certainly much greater and lots of organic material might have been delivered by large meteorites; however, it's unlikely that amino concentrations in the oceans could ever have been more than 10-100 pM for all amino acids combined.

Most amino acids will spontaneously degrade over time. There's a window of opportunity that only lasts about 10 million years because in that time all the water in the oceans will pass through hydrothermal vents and the high temperature will destroy most chemicals—including amino acids.
I don't know whether the NASA astronomers are aware of this problem but have developed a scenario to overcome it, or whether they just haven't thought about the problem.


Bada, J. (1991) Amino acid cosmogeochemistry. Phil trans. R. Soc. Lond. 333:349-358.

2 comments :

  1. Larry Moran wrote: Most scientists are not thinking critically about the origin of life. It is extremely improbable that asteroids could have delivered enough amino acids or purines to make a difference. Given the known stability of these molecules in the ocean, you would have to achieve an enormous delivery rate to make a concentration sufficient to drive polymerization.

    Agreed completely, but never mind polymerization. How do NASA astrobiologists propose to link the bases with (dexoy?)ribose at the 1' carbon and Phosphate at the 5' end in the prebiotic environment?

    Simply having some obscure Purine or Pyrimidine dilution doesn't DeoxyriboNucleicAcids make.

    I'm extremely interested in the research on the origin of life(who isn't? Oh yeah, IDiots!), but these silly "tiny piece of compound X, Y or Z has been detected in an interstellar cloud with an average distance of 100 meters between individual molecules" - aren't presenting us with any clues or remotely plausible avenues of research.

    Now, people like Wächterhauser(Iron-sulfur world-theory, hydrothermal vents etc. etc.) had some good ideas, we need more people (with money and resources) like that to do useful research.

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  2. They probably haven't thought about how long the bases would last. Their presence is interesting mainly as evidence that delicate organic molecules could form by simple chemical processes. If it could happen in space, it could happen on Earth and is much more likely given the greater density of reagents.

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