NASA Astrobiology Institute (NAI)

1. Chemistry and biology of ultramafic-hosted alkaline springs

   Project Investigators: Michael Mottl

   Other Project Members

   Thomas McCollom (Collaborator)

   Summary

   Ultramafic rock makes up Earth’s mantle and is an abundant material in the inner solar system. When water is added it converts to serpentinite, producing in the process H₂ and, when CO₂ is present, methane, both of which are ideal fuels for microbial activity. We are studying serpentinite mud volcanoes in the Mariana forearc, where water ascends from the subducting Pacific plate into the overlying mantle, producing large volumes of serpentinite that exhibits unusual fluid chemistry (e.g., pH 12.6) and extremophilic microbial activity, as an analog to extraterrestrial environments such as on Mars and the asteroids.

   Astrobiology Roadmap Objectives:

   • Objective 5: Describe the sequences of causes and effects associated with the development of Earth's early biosphere and the global environment.
   • Objective 7: Identify the environmental limits for by examining biological adaptations to extremes in environmental conditions.

   Project Progress

   We have determined that these methane-rich waters, which are the highest pH waters ever found on Earth, support abundant Archaea that anaerobically oxidize methane (AOM) to carbonate while reducing sulfate, all at an in-situ pH of 13.1. Such a high pH cannot be generated by serpentinization alone. In collaboration with Dr. Tom McCollom of the Unversity of Colorado NAI, and with additional funding from NSF, we are modeling the processes that generate this extreme environment, including 1) dehydration and dissolution of subducted organic and inorganic carbon from the subducting oceanic plate with increasing temperature and pressure; 2) ascent of this water and dissolved carbon and its input into the ultramafic rock of the overriding plate; 3) serpentinization of this rock and accompanying generation of H₂; 4) reaction of H₂ with carbon to make methane that ultimately fuels extremophilic (high pH) microbial communities in the shallow subseafloor. This methane is abiogenic, so this process may be analogous to what may be happening on Mars.

   Mission Involvement

   Mars Reconaissance Orbiter

   Investigates possible source of abiogenic methane

   Mars Express

   Investigates possible source of abiogenic methane

   Mars Science Lab

   Investigates possible source of abiogenic methane

   Field Expeditions

   Name

   Sampling Mariana Forearc Serpentinite Mud Volcanoes

   Dates

   March 22, 2003 - May 4, 2003

   Location

   14N 146E

   Description

   We cored ten serpentinite mud volcanoes in the Mariana forearc, recovering serpentinite, included pore water, and microbes.

   Cross-Team Collaborations

   Tom McCollom, University of Colorado NAI, with whom I have collaborative research funding from NSF to study serpentinization and microbial activity in the Mariana forearc.

Publications

Meech, K.J. & Mottl, M.J.  (2008).  Origin of Earth's water - current key issues.  Astrobiology, 8.

Mottl, M.J., Glazer, B.T., Kaiser, R.I. & Meech, K.J.  (2008).  Water and Astrobiology.  Chemie der Erde, 67:253-282.