A Metal Key To Life

A new model of abiogenesis, the formation of life from inanimate matter, is proposed in the current issue of "The Biological Bulletin "and may bring us one step closer to answering one of biology's longest standing questions: how did life begin? The problem of how life originated from non-living matter has been particularly tricky because all life as we know it requires both DNA for information storage and proteins to catalyze the formation of DNA. Both are complex molecules and both seem to be essential. So which came first, the DNA or the proteins?

The commonly accepted answer has been that RNA, or ribonucleic acid, performed both the information storage and catalyzing functions. This is known as the "RNA World Hypothesis". Studies have shown RNA does exhibit autocatalytic properties. That is, an RNA molecule can facilitate its own reactions with other molecules. While this RNA "bootstrapping" has been viewed as the most reasonable explanation for the origin of self-replicating organic systems, the inherent complexity of RNA molecules and the argument's circular nature have been troublesome.

The recent proposal by Morowitz, Srinivasan, and Smith is that organo-metallic compounds, originating near deap-sea hydrothermal vents, provided the initial catalysis required for the formation of a more complex and self-sustaining system of organic molecules. Hydrothermal vents have been considered as candidate sites for the formation of life since their discovery in the 1970's and the present model is one of several proposed mechanisms by which living systems could arise.

These mechanisms, which rely on geothermal and chemical energy, have deep implications for the search for life beyond Earth. A solar system's "habitable zone" is often depicted as existing at only a narrow range from the system's central star, where the solar energy received is sufficient to maintain liquid water at the planet's surface. This view seems to provide a rather limited set of environments hospitable to the evolution of life. However, if life can indeed arise from the biogeochemical processes around hydro-thermal vents, virtually any geologically active world with liquid water (even if it is only restricted to the area of hydro-thermal activity) could harbor life. Thus Europa, an icy but geologically active moon of Jupiter, has become a prime target in the search for alien life. Given the environmental stability provided by deep-sea hydrothermal environments, and the apparent abundance of life around such sites on Earth, Europa's icy seas are well worth exploring.

Video: Deep Sea Vents and Exploring Europa

Full Scientific Paper

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