[Campbell Biology P.82] Carbon-14 dating is effective for fossils up to about 75,000 years ... | Practice Question

Carbon-14 dating is effective for fossils up to about 75,000 years old. Why is Carbon-14 unsuitable for dating dinosaur bones which are typically 65.5 million years old , and what alternative radioactive isotope might be more appropriate, according to the text?

  • A: 14C is too stable for old fossils; Uranium-235 with a half-life of 704 million years.
  • B: Dinosaur bones are too small for 14C dating; Potassium-40 with a half-life of 1.3 billion years.
  • C: 14C decays too quickly, leaving too little to detect in dinosaur bones; Uranium-235 with a half-life of 704 million years.
  • D: Dinosaur bones do not contain carbon; Thorium-232 with a half-life of 14 billion years.

Explanation

The text states that 'Carbon-14 dating works for fossils up to about 75,000 years old; fossils older than that contain too little 14C to be detected.' Since dinosaurs went extinct 65.5 million years ago, their bones are far too old for 14C dating. The text then suggests that '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?' implying it would be suitable due to its much longer half-life.