Oxygen-18 is a stable isotope of oxygen, meaning it has a consistent number of protons and neutrons in its nucleus. It contains eight protons and ten neutrons, making it heavier than the more common isotopes, Oxygen-16 and Oxygen-17. Oxygen-18 is naturally occurring and can be found in water and carbon dioxide in the environment. This isotope plays a significant role in various scientific fields, including paleoclimatology and geochemistry. Researchers often use oxygen-18 to study past climate conditions by analyzing ice cores and sediment samples, as the ratio of oxygen isotopes can provide insights into historical temperatures and precipitation patterns.