Monday, September 13, 2010

PAHs and the development of life

If you've ever been curious about the origin of life and how it arose from nonliving molecules, for the past few years there's a mindblowing new scenario on how that could have happened centered around Polycyclic Aromatic Hydrocarbons as an intermediate "starter" stage that leads to life. Not because of PAH's complexity, but because of how durable they are, how simple they are.

PAHs, in short, are polycyclic because they are typically carbon atoms that form into extremely durable ring structures, connected to each other. As anyone that's ever played with a molecular model kit knows, carbon atoms connect at angles that result in a cyclic shape. Because the carbon atoms double-bond to each other over and over, they have a real toughness by sharing bonds, a property in chemistry known as "aromatic."

PAHs are found over and over on earth, and in fact are even one polycyclic aromatic molecule (though not a hydrocarbon), C60, was the first soccer-ball shaped buckminsterfullerine ever discovered in nature, a sexy kind of molecule that gets a lot of attention because of unique properties. Flatten a buckyball out into a sheet of graphene (well, more or less), curl it up and you get carbon nanotubes, a molecule with the primary property of creating tons and tons of work for sensationalist science writers prone to jumping the gun.

Amusingly enough, one PAH is Naphthaline, C10H8, which is the primary ingredient of mothballs.

Not only is C60 as well as PAHs found in interstellar space where the primary components of life are believed to be found, the strong bonded structure means it can tolerate resistance and survive untouched in space, surrounded by UV light that would break up and destroy more fragile components of organic chemistry, like amino acids. Likewise, they're far simpler, just basic ring-shaped hydrocarbons that because the cyclic shape repeats over and over, it remains intact even if blown apart. It is believed they could have formed primitive membranes that protected life, helped in metabolism, and can even hold genetic information...the only material known in the interstellar medium that meets all three criteria for life.

Because of their stability and resistance to temperature and radiation, if PAHs played a role in the development of life on earth, it would change the conditions that are required for life to form, which may mean that life can develop in environments more deadly and dangerous than previously thought.


  1. PAHs are carcinogenic, and so unlikely to be involved in the formation of life.

    PS. It's naphthalene, not naphthaline

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