Please choose the correct answer to the question: Which best describes how ice cores are important to the study of geologic history?

Answer1: They show unconformities, which signal changes in deposition. Answer2: They hold index fossils, which are used to date the different ice cores. Answer3: They contain evidence showing changes in the atmospheric composition over time. Answer4: They follow the Law of Superposition, which gives reasons for extinctions of species.

Answer format: answer1/answer2/answer3/answer4