It's that you need to go to a place that's a desert today, a place that doesn't have too many plants covering up the rocks, and a place where erosion is always exposing new bones at the surface.
你需要去沙漠的原因是， 沙漠中的岩石没有太多植被覆盖 并且其风蚀能够使岩石暴露于地表。