Which of the following evidences of evolution employs the use of radio-isotope dating?

Step 1: Analyze the question The question asks which line of evidence for evolution uses radio-isotope (radiometric) dating, a method for finding the age of materials.

Step 2: Explain the concept Radio-isotope dating, such as carbon-14 dating or uranium-lead dating, measures how much of a radioactive isotope has decayed into its stable product. Each isotope decays at a known rate called its half-life, so the ratio of parent to product tells us how old a sample is.

• Carbon-14 (half-life about 5,730 years) is used for relatively recent organic remains.
• Uranium-238 and potassium-40 (half-lives of millions to billions of years) are used for dating the rocks that contain very old fossils.

Step 3: Go through the options

• A. Comparative anatomy: compares structures across species, such as the forelimbs of humans, bats and whales. It involves no dating.
• B. Embryology: compares the early developmental stages of different organisms. It involves no dating.
• C. Fossil records: fossils are preserved remains of ancient organisms. Their ages are worked out by radio-isotope dating of the fossils or the rock layers around them, which lets scientists arrange organisms in time and trace how life has changed.
• D. Vestigial organs: reduced structures with little or no function, such as the appendix. They are studied by comparison, not by dating.

Step 4: Answer Only the fossil records use radio-isotope dating, so the correct option is C.

Step 5: Exam tip Link the words: "dating" = "fossils". If you see carbon dating, half-life, or the age of rocks in a question about evolution, think fossil records. Also remember that comparative anatomy, embryology and vestigial organs are all about comparing structures, not measuring age.