Uranium-238 is a radioactive element that will decay into lead-206. It has a half-life of 4.5 billion years, which means that after 4.5 billion years exactly one-half of the total amount of uranium-238 that you started with will have decayed into lead-206. Suppose you were given a 100-gram, solid block of uranium-238, and you buried it in the ground. Nine billion years from now, if someone dug it up and analyzed it, how much uranium-238 would be left?