The age of a fossil can often be determined using radiometric dating of the rocks in which the fossil is found. Because uranium-238 has a half-life of 4.5 billion years, it means that:
A. when it is 9 billion years old, a rock will have no uranium-238 remaining.
B. when the earth is 9 billion years old, no uranium-238 will exist.
C. a uranium-containing rock that is 4.5 billion years old would, today, have only about half as much of its uranium in the form of radioactive uranium-238 as a rock that was just recently formed.
D. uranium-238 cannot be used to establish the age of fossils greater than 4.5 billion years old.
Answer: C. a uranium-containing rock that is 4.5 billion years old would, today, have only about half as much of its uranium in the form of radioactive uranium-238 as a rock that was just recently formed.
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