Oxygen-18 is a stable isotope of oxygen, meaning it does not undergo radioactive decay. It has eight protons and ten neutrons in its nucleus, making it heavier than the more common Oxygen-16, which has eight protons and eight neutrons. Oxygen-18 is naturally found in water and is often used in scientific research, particularly in studies related to climate change and paleoclimatology. This isotope plays a crucial role in understanding past temperatures and precipitation patterns. By analyzing the ratio of Oxygen-18 to Oxygen-16 in ice cores and sediment samples, scientists can infer historical climate conditions and make predictions about future climate trends.