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Summary
Somewhere in the sediments and rocks beneath the ocean floor, it gets too hot for living things. But how far down? Even after drilling kilometers into the ocean floor, scientists have found that microbes persist. Rather than going for depth, then, a new drilling expedition embarking this month off the coast of Japan will search for the high temperature at which microbial life stops in the deep biosphere. Part of the International Ocean Discovery Program, the T-Limit campaign could guide estimates of the abundance and diversity of ocean floor microbes, which play large roles in biogeochemical cycles. Demonstrating the absence of life will be challenging, however, and push the limits of existing methods.