The continental lithosphere hosts geochemically active and diverse microbial ecosystems, or deep life, that comprise roughly half of the Earth’s microbial biomass. However, opportunities to study deep life have been limited.
The coring of continental settings for microbiology began with Soviet scientists examining petroleum-bearing sediments in the 1950s and gained momentum in the mid-1980s with support from the U.S. Department of Energy and the U.S. Geological Survey. The Deep Sea Drilling Project (now the Integrated Ocean Discovery Program (IODP)) also began exploring the subseafloor biosphere in the 1980s. Since 2000, IODP has supported several highly successful microbially focused coring expeditions, beginning with Leg 201’s exploration of the Peruvian continental margin.
The International Continental Scientific Drilling Program (ICDP) is the land-based counterpart of IODP. Although deep life has been an ICDP theme since its inception, deep-life studies have so far only piggybacked on drilling for other purposes. No ICDP project has ever been conceived and executed with deep life as the primary objective.
In part, this failing stems from the lack of competitive projects proposed by the deep-life community. A workshop was organized, therefore, to develop one or more deep-life continental drilling proposals.
Nineteen scientists from eight countries met in early November at the German Research Centre for Geosciences (GFZ) in Potsdam, Germany, with support from the Deep Carbon Observatory (DCO) and ICDP. Participants discussed targeting previously unexplored, yet globally significant, deep-life habitats and biomes on the basis of physical (temperature, pressure, porosity), geological (sedimentary versus igneous), geohydrological (high versus low biome interconnectivity), and geochemical (salinity and low organic carbon and abiotic hydrogen versus organic-rich shale) parameters.
Workshop attendees agreed to a number of specific criteria for selecting and developing the strongest possible proposals. Specifically, the projects should
- meet the DCO Decadal Goals
- meet the ICDP selection criteria
- start with a reasonable understanding of site characteristics
- focus on areas with high physical, geochemical, and biological diversity
- focus on areas that have a high probability of active microbial communities
- explore the potential to transect the depth and temperature limit for life
- select sites that are accessible, preferably with long-term access to the completed borehole(s)
The participants heard presentations on 10 proposed drilling sites. These included the Basin and Range Province (United States), the Eger Rift (Czech Republic), an active fold and thrust belt (Taiwan), ancient evaporite deposits (Europe), Phanerozoic (450–350 million years old) black shale interfaces (United States), the Deccan Traps (India), Precambrian (2 billion years old) metamorphic and igneous rocks (Finland), subglacial basaltic aquifers (Iceland), and subpermafrost sediments (Canada). Deltaic fans (or megafans) and ophiolite complexes were also discussed.
ICDP executive secretary Uli Harms advised project proponents on proposal preparation. As a result of this meeting, one of the attendees submitted a proposal for an ICDP-sponsored drilling workshop (the first step in the ICDP process) on 15 January. Other attendees plan to submit drilling workshop proposals within the next 2 years. These workshops will provide opportunities for continental deep-life investigators to reach out to the Earth science community and build momentum for these deep-life-driven drilling projects.
–Tullis C. Onstott, Princeton University, Princeton, N. J.; email: [email protected]; and Thomas L. Kieft, New Mexico Institute of Mining and Technology, Socorro
Citation: Onstott, T. C., and T. L. Kieft (2015), Developing deep-life continental drilling projects, Eos, 96, doi:10.1029/2015EO024937. Published on 26 February 2015.