They show unconformities, which signal changes in deposition. They hold index fossils, which are used to date the different ice cores. They contain evidence showing changes in the atmospheric composition over time. They follow the Law of Superposition, which gives reasons for extinctions of species.
I gave my students this multiple choice question: Which best describes how ice cores are important to the study of geologic history?

Only one answer is correct among these 4 choices:
- They show unconformities, which signal changes in deposition.
- They hold index fossils, which are used to date the different ice cores.
- They contain evidence showing changes in the atmospheric composition over time.
- They follow the Law of Superposition, which gives reasons for extinctions of species.

Could you tell me which one is correct?

They contain evidence showing changes in the atmospheric composition over time.