Final answer:
The student's question touches on the use of isotopes in archaeology and medicine, with Oxygen-18 serving as an example that aids in understanding past environmental conditions and is also important in medical treatments like cancer therapy.
Step-by-step explanation:
The subject matter of the student's question primarily concerns the use of isotopes in fields such as archaeology and medicine. In the context of archaeology, isotopes like Oxygen-18 are utilized for radioactive dating which helps determine the geological history of the Earth and has applications in paleoclimatology. As evidenced in the example given, the ratio of Oxygen-18 to Oxygen-16 in an ice core can be used to infer past temperatures, providing insights into environmental conditions of different eras. Isotopes are also critical in medicine, for instance, when radioactive cobalt emits gamma rays to target cancer cells in therapies.