Thursday, September 3, 2009

Mars Jars Don't Work - But Zinc Might

"New Origin of Life Proposed: Zinc & Zap " (September 3, 2009)

"The Miller-Urey experiment, conducted by chemists Stanley Miller and Harold Urey in 1953, is the classic experiment on the origin of life. It established that the early Earth atmosphere, as they pictured it, was capable of producing amino acids, the building blocks of life, from inorganic substances.

"Now, more than 55 years later, two scientists are proposing a hypothesis that could add a new dimension to the debate on how life on Earth developed.

"Armen Mulkidjanian of the University of Osnabrueck, Germany and Michael Galperin of the U.S. National Institutes of Health present their hypothesis and evidence in two papers published and open for review in the web site Biology Direct...."

Scientists have been learning more about what's been happening, and thrashing out increasingly less improbable models for explaining how places like Earth develop. Not all that long ago, it was reasonable to assume that this planet had a 'reducing atmosphere' early on:

"...Miller and Urey replicated the early Earth atmosphere with a mixture of methane, hydrogen, ammonia and water vapor. This mixture, along with some "sparks" which simulated lightning, led to the formation of amino acids. With this setup, Miller and Urey assumed that the early Earth had a reducing atmosphere, which meant it had large amounts of hydrogen and almost no oxygen...."

I remember when "Mars jars," complete with electrical sparks, were all the rage. And, sure enough, amino acids formed in them. They looked cool, reminded me of mad scientists' laboratories in the old movies: and were based on reasonable assumptions.

Just one problem. Now it looks like Earth's atmosphere was chemically neutral. Sort of like what Mars has now, except thicker. With small amounts of nitrogen and hydrogen.

An atmosphere like that still has the chemical makings of amino acids - but they won't form in the traditional Mars jars. It's been tried.

New Data, Model

The sort of atmosphere that Earth's assumed to have had could have produced amino acids - but through a different mechanism.

"...The scientists suggest that life on Earth originated at photosynthetically active porous structures, similar to deep-sea hydrothermal vents, made of zinc sulfide (more commonly known as phosphor). They argue that under the high pressure of a carbon-dioxide-dominated atmosphere, zinc sulfide structures could form on the surface of the first continents, where they had access to sunlight. Unlike many existing theories that suggest UV radiation was a hindrance to the development of life, Mulkidjanian and Galperin think it actually helped...."

They could be right. I wouldn't bet that this is the last word in the story of what mechanisms were involved in getting mushrooms, eagles, and sequoias started: but it doesn't sound all that unlikely.

I've been following studies of how life may have started for about four decades now, and am impressed by a pattern. From the Mars jars to the Mulkidjanian-Galperin work, each successive best-estimate of what happened several billion years back has been matched with a fairly simple, plausible explanation for how life could have started - or at any rate, the bricks that life is made of.

It looks to me like life's components may not be the long shot that some authors have claimed.

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