Final answer:
Isotopes are atoms of the same element with different neutron numbers. Oxygen-18 is an isotope used in paleoclimatology to determine past climate and numerical dates.
Step-by-step explanation:
Isotopes are atoms of the same element that have different numbers of neutrons. They have the same number of protons and electrons, but different mass numbers. One example of an isotope is Oxygen-18, which is used in paleoclimatology to determine past climate and numerical dates. Scientists can analyze the ratio between Oxygen-18 and Oxygen-16 in an ice core to calculate the temperature of the environment in the past.