by Nicholas T. Arndt, Paul R.D. Mason, Allan Wilson, Axel Hofmann, Gary Byerly

The Barberton Greenstone Belt in South Africa is one of the best-preserved successions of mid-Archean (3.5-3.2 Ga) supracrustal rocks in the world, and, as such, it is a remarkable natural laboratory where conditions and processes at the surface of the Archean Earth can be studied in detail. Despite generally good outcrop, nowhere in the Barberton belt are complete field sections preserved, and crucial features such as the contacts of lava flows and continuous successions of critical sedimentary rock sequences are not exposed. Only through diamond drilling will it be possible to obtain the continuous sections and relatively unaltered samples through the volcano-sedimentary successions. Two main targets have been identified. (1) Sedimentary sequences, which will provide information about erosion and sedimentation on the early Earth, the composition and temperature of Archean seawater, and one possible site where life may have emerged and evolved. Study of tidal sequences will provide information about the dynamics of the Earth-Moon system, and the investigation of spherule layers (including impact debris) provide information about the nature and magnitude of meteorite impacts on the early Earth. (2) Successions of ultramafic to felsic volcanic rocks, which will provide new insights into volcanic processes, dynamics of the crust and mantle, interaction between oceanic volcanic crust and the hydrosphere and biosphere. The sources of hydrothermal fluids on the ocean floor, driven by circulation of seawater through the volcanic pile, constitute a second habitat of early life. The project is supported by scientists from 13 countries in five continents and by the mineral exploration industry. The choice of targets, drilling strategies and scientific goals were discussed in detail during planning meetings held in Johannesburg (October 2006), San Francisco (December 2006) and Berlin (March 2007) and during a one-week field conference in the Barberton belt in September 2007. The drilling of a series of shallow (150 to 800m) holes is planned for late 2009 or early 2010 and drill core will be available for distribution six months later. The drilling will be conducted using a standard rig and conventional technology under the supervision of experienced geologists from South African universities and mineral exploration companies. Local logistics will be handled by local geologists in cooperation with staff from the Council of Geosciences. The distribution of samples and post-drilling research will be coordinated by a steering committee comprising representatives from all major participating countries.

• Our aim is to investigate conditions on the early Earth functioned and particularly those in which life emerged and evolved. Through the investigation of cores recovered through shallow drilling in the sedimentary and volcanic sequences of the 3.5 to 3.2 Ga Barberton belt, we will address the following issues - Sedimentological and geochemical investigations of clastic sedimentary rocks will provide information on erosion, transport and deposition under Archean conditions beneath an aggressive atmosphere and of vegetation-free land surfaces - Studies of well-preserved tidal sequences will place constraints on the dynamics of the Earth-Moon system - Investigation of spherule layers, believed to be composed of impact glasses, will provide information about meteorite flux - Petrological and chemical studies of komatiites will provide information about the temperature and geodynamic activity in the Archean mantle - Analysis of zones affected by hydrothermal alteration in the volcanic series will be used to establish the composition and structure of Archean oceanic crust, and the manner in which it interacted with Archean ocean waters - Geochemical and stable isotope studies of cherts and silicified volcanic and sedimentary rocks will be used to determine the temperature and composition of Archean ocean waters - Microbiological studies of recovered core will be used to characterize the modern deep biosphere beneath the Archean greenstone terrane - A combination of micropaleontology, biochemistry and biogeochemistry will be used to search for and characterize traces of early life in the sedimentary and volcanic rocks.

Africa, Archean, BARBERTON, Barberton Cradle Of Life, BARBERTON_C, Composition Of Ocean And Atmosphere, Habitat Of Early Life, ICDP-2009/01, Komatiite, Sediment, South Africa, Surface Processes, Volcanic

Latitude: -25.982, Longitude: 30.84194