The half life of uranium-235 is 4.5 billion years. If 0.5 half-lives have elapsed, how many years have gone by? A. 4.5 billion
B. 9 billion
C. 2.25 billion
D. 4 billion ​

C. 2.25 billion years

Explanation:
If one half life has elapsed, 4.5 billion years will have gone by. Half of a half life has elapsed, so half of 4.5 billion years will have gone by. 4.5 billion years divided by 2 is 2.25 billion years.

It would be the equator.