Here's a problem to solve: Which best describes how ice cores are important to the study of geologic history?

Among the 4 following options, which is the correct answer?

- A: They show unconformities, which signal changes in deposition.
 
- B: They hold index fossils, which are used to date the different ice cores.
 
- C: They contain evidence showing changes in the atmospheric composition over time.
 
- D: They follow the Law of Superposition, which gives reasons for extinctions of species.
 