Given a scientific question and its correct answer, generate supporting facts for the answer. This supporting fact can be an explanation for the answer to the given question.

[Q]: Question: Differences in fitness among different members of a population can lead to what kind of selection? Answer: natural selection
[A]: Natural selection occurs when there are differences in fitness among members of a population.

[Q]: Question: What is the point on the ground that is located directly above where underground rocks fracture (or the "focus" point)? Answer: epicenter
[A]: The focus is where the rocks rupture. The epicenter is the point on the ground directly above the focus.

[Q]: Question: What is another term for scale worms? Answer: halkieria
[A]:
Halkieria, or scale worms, are an example of a fossil life from the Cambrian.