At Site 1156, four rock samples were collected as soon as the core liners were split to characterize the microbial community (Table T2). Three samples are pillow basalt fragments, composed of partially altered glass rinds and crystalline basalt interiors (Samples 187-1156A-3R-3 [Piece 1, 0-3 cm], 187-1156B-2R-1 [Piece 14, 93-97 cm], and 187-1156B-6R-1 [Piece 4, 50-54 cm]) and one is crystalline basalt (Section 187-1156B-5R-1 [Piece 7]). To minimize drilling-induced contamination, the outer surfaces of the rock samples were quickly flamed with an acetylene torch. Enrichment cultures and samples for DNA analysis and electron microscope studies were prepared for each sample (see "Igneous Rocks" in "Microbiology" in the "Explanatory Notes" chapter).
To examine the extent and type of contamination caused by drilling fluid, fluorescent microsphere tests were carried out for Cores 187-1156A-3R and 187-1156B-2R (see "Tracer Test" in "Microbiology" in the "Explanatory Notes" chapter and Table T2). Pieces of rock were rinsed in nanopure water, the collected water was filtered, and the filters were examined for the presence of microspheres under a fluorescence microscope. Thin sections from the inner parts of the rocks were also examined. In the thin sections, microspheres were located both in fractures and on the thin-section surfaces. All were close to the thin-section (i.e., piece) margins. Those on the surface may have been relocated by polishing. Fifteen microspheres were observed in thin sections from Core 187-1156A-3R and six from Core 187-1156B-2R.