Water-filled micropores in hot rock may have acted as the
nurseries in which life on Earth began. A team at
Ludwig-Maximilians-Universitaet (LMU) in Munich has now shown that temperature
gradients in pore systems promote the cyclical replication and emergence of
nucleic acids.
How
and in what habitats did the first life-forms arise on the young Earth? One
crucial precondition for the origin of life is that comparatively simple
biomolecules must have had opportunities to form more complex structures, which
were capable of reproducing themselves and could store genetic information in a
chemically stable form. But this scenario requires some means of accumulating
the precursor molecules in highly concentrated form in solution. In the early
oceans, such compounds would have been present in vanishingly low
concentrations. But LMU physicists led by Professor Dieter Braun now describe a
setting which provides the necessary conditions. They show experimentally that
pore systems on the seafloor that were heated by volcanic activity could have
served as reaction chambers for the synthesis of RNA molecules, which serve as
carriers of hereditary information in the biosphere today.
"The
key requirement is that the heat source be localized on one side of the
elongated pore, so that the water on that side is significantly warmer than
that on the other," says Braun. Preformed biomolecules that are washed
into the pore can then be trapped, and concentrated, by the action of the
temperature gradient -- thus fulfilling a major prerequisite for the formation
and replication of more complex molecular structures. The molecular trapping
effect is a consequence of thermophoresis: Charged molecules in a temperature
gradient preferentially move from the warmer to the cooler region, allowing
longer polymers in particular to be securely trapped. This is an important
factor in the evolution of nucleic acids such as RNA and DNA, simply because
longer molecules can store more genetic information
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