In the absence of photosynthesis, life faces significant challenges. Despite this, the earliest life on our planet must have found a way to survive. Several controversial hypotheses have been posited, of which a number focus on hydrogen production at water-rock interfaces. A recent paper published this month (June 2013) in Nature Geosciences by DCO scientists suggests that these reactions can indeed occur at temperatures that could support primitive life .
Serpentinization reactions (hydration of ultramafic rocks) have been well documented, and result in the production of metabolically relevant chemicals including hydrogen and methane (recently reviewed by McCollom and Seewald ). Hydrogen from such reactions fuels ecosystems, such as the Lost City hydrothermal vent community . However, whether similar reactions occur at high enough rates to sustain life at temperatures tolerable to known life forms is uncertain.
To address this problem, Mayhew and colleagues took natural samples of iron-rich rocks and minerals (peridotite, olivine, fayalite, magnetite, and petedunnite) and incubated them with sulphate-free artificial seawater at both 55 and 100°C. While the authors noticed considerable variation, hydrogen gas was produced in significant quantities in most conditions.
The mechanism of reaction, however, remains puzzling. One facet united all of the samples that initially produced hydrogen rapidly: the presence of crystal surfaces with spinel atomic structure. Mayhew and colleagues suggest that these surfaces catalyze oxidation of iron by water. However, the rate of reaction does not vary in an obvious way with spinel abundance, leaving open possibilities that spinel composition and surface area may be crucial variables.
In an accompanying News and Views article, Deep Life’s Steven D’Hondt addresses these issues in detail .
This research adds credence to ideas proposed over 20 years ago that hydrogen-based ecosystems could survive in the absence of any influence from photosynthetic life. Developing experimental systems such as this, or discovering natural environments where such ecosystems thrive, is crucial if we are to answer fundamental questions about the origin of life on our planet, or the potential for non-photosynthetic life in extraterrestrial habitats.
Photo Credit: Remnants of Ancient Streambed on Mars (White-Balanced View) NASA/JPL-Caltech/MSSS