Last modified on: 10/06/2015
Making organic molecules in hydrothermal vents in the absence of life


In marine sciences Scientists from Woods Hole Oceanographic Institution embarked on a NASA-funded mission to the Mid-Cayman Rise in the Caribbean, in search of a type of deep-sea hot-spring or hydrothermal vent that they believed held clues to the search for life on other planets. They were looking for a site with a venting process that produces a lot of hydrogen because of the potential it holds for the chemical, or abiotic, creation of organic molecules like methane--possible precursors to the pre-biotic compounds from which life on Earth emerged. For more than a decade, the scientific community has postulated that in such an environment, methane and other organic compounds could be spontaneously produced by chemical reactions between hydrogen from the vent fluid and carbon dioxide (CO2). The theory made perfect sense, but showing that it happened in nature was challenging.


New research by geochemists at Woods Hole Oceanographic Institution reported in the proceedings of the National Academy of Sciences that methane formation does not occur during the relatively quick fluid circulation process, despite extraordinarily high hydrogen contents in the waters. While the methane in the Von Damm vent system they studied was produced through chemical reactions (abiotically), it was produced on geologic time scales deep beneath the seafloor and independent of the venting process. Further studies reveals that another organic abiotic compound is formed during the vent circulation process at adjacent lower temperature, higher pH vents, but reaction rates are too slow to completely reduce the carbon all the way to methane. Methane and other organic compounds in natural waters can originate from three types of sources: living organisms, decomposition of living or dead biomass, and 'abiotic' formation via purely chemical processes with no participation from living organisms. Finding out how methane and other organic species are formed in deep-sea hydrothermal systems is compelling because these compounds support modern day life, providing energy for microbial communities in the deep biosphere, and because of the potential role of abiotically-formed organic compounds in the origin of life.




Jill M. McDermott, Jeffrey S. Seewald, Christopher R. German, and Sean P. Sylva. Pathways for abiotic organic synthesis at submarine hydrothermal fields. PNAS, June 8, 2015 DOI: 10.1073/pnas.1506295112