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In a 2018 study, Ceri Shipton et al. concluded that stone tools excavated from an archaeological site in Saudi Arabia date to between 197,000 and 276,000 years ago. The reliability of the dates that Shipton et al. have posited, which were obtained through processes that determined when buried mineral grains surrounding the tools were last exposed to sunlight, _____ in part upon the researchers' exclusion of mineral grains that lacked adequate sun exposure before burial.