A scientist finds the bones of a dinosaur. What could help the scientist determine the approximate age of the dinosaur bone?

• A. the birds living in the area of the bones
• B. the weather conditions in the area of the bones
• C. the kinds of trees living in the area of the bones
• D. the index fossils in the area of the bones

Answer: (D)

Dating a dinosaur bone usually relies on the rocks and fossils found with it. A key way scientists estimate age is by using index fossils—fossils of species that existed for a relatively short time but were widespread. When the bone is in the same rock layer as an index fossil with a known time range, that shared layer can be dated to that narrow window. So, finding those index fossils around the bone gives a good estimate of when the dinosaur lived.

For example, if the surrounding rock contains an index fossil known to have lived only during a specific range, the bone is likely from roughly that same time. This method is about tying the bone to a time marker in the rock layer.

Other factors like birds currently living in the area, past weather conditions, or the kinds of trees in the area don’t provide precise dates for the dinosaur bone. They can tell about the environment or climate, but they don’t pin down when the bone formed the way index fossils do.