By Kenneth Chang
WITWATERSRAND BASIN, South Africa — A mile down in an unused mine tunnel, scientists guided by helmet lamps trudged through darkness and the muck of a flooded, uneven floor.
In the subterranean world of the Beatrix gold mine, they shed their backpacks, taking out tools and meticulously prepared test tubes to collect samples.
Leaning a ladder against the hard rock wall, Tullis C. Onstott, a geosciences professor at Princeton, climbed to open an old valve about a dozen feet up.
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