Radioactive uranium-235 has a half-life of 704 million years. If it was incorporated into dinosaur bones, could it be used to date the dinosaur fossils?

Question

No, only about one tenth of the 235U would have decayed after 65.5 million years, not leaving enough to measure in the fossils.
No, the dinosaurs went extinct too recently to use a radioisotope with a half-life of 704 million years.
Yes, but only for dinosaurs that lived more than 704 million years ago.
Yes, after 65.5 million years only about one tenth of the 235U would have decayed, leaving plenty to measure in the fossils.

Answer 1

The correct response is:

No, only about one tenth of the 235U would have decayed after 65.5 million years, not leaving enough to measure in the fossils.

Uranium-235 has a very long half-life (704 million years), and since dinosaurs went extinct approximately 65.5 million years ago, the amount of uranium-235 that would have decayed during that time would be minimal. After 65.5 million years, only about 9% (or roughly one-tenth) of the original amount would have decayed, which may not be sufficient for accurate measurement and dating in fossils. Therefore, uranium-235 is not suitable for dating dinosaur fossils. Other methods, such as carbon-14 dating, are more applicable for more recent specimens, but even that has limitations due to its half-life of 5,730 years.