The table below shows the half-life of an element: half-life data element half-life uranium-235 700 million years scientists have found that the uranium-235 content of an unknown prehistoric sample was reduced to one-fourth. what best describes the identity of the sample? a stone artifact that formed 700 million years ago a mammoth that died 1,400 million years ago a cliff that formed 1,400 million years ago a plant that died 700 million years ago