A broad region, nearly the size of the Mediterranean Sea, exists in the central South Pacific Ocean that is devoid of sediment and has been so since the Late Cretaceous. The requirements for remaining sediment free are very low biological productivity, a shallow calcite compensation depth, essentially no dust input, and no deposition of hydrothermal oxides and hydroxides. One or two of these conditions are common, but nowhere else do all four occur. The combined effect of these sediment-inhibiting factors is a consequence of crustal age, seawater chemistry, and atmospheric, oceanographic, and physiographic isolation. Furthermore, this unique combination of conditions has prevailed for more than 80 million years.