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Oxygen isotope ratio cycles are cyclical variations in the ratio of the mass of oxygen with an atomic weight of 18 to the mass of oxygen with an atomic weight of 16 present in calcite of the oceanic floor as determined by core samples. The ratio is linked to water temperature of ancient oceans, which in turn reflects ancient climates. Cycles in the ratio mirror climate changes in geologic history.Connection between isotopes and temperatureO-18 is two neutrons heavier than O-16 and causes the water molecule in which it occurs to be heavier by that amount. The addition of more energy is therefore required to vaporize it than for O-16, and the molecule must lose less energy to condense.Energy adds to or takes from the vibrational motion of the molecule, expressed as temperature. At the boiling point, the vibration is sufficiently high to overcome the adhesion between water molecules and they fly into the space of the container or the atmosphere. At the dew point, the molecules adhere into droplets and fall out of the atmosphere as rain or snow. Below the boiling point, the equilibrium between the number of molecules that fly out and the number that return is a function of water temperature.A warmer water temperature means that the molecules require less energy to vaporize, as they already have more energy. A cooler water temperature means that the water requires more energy to vaporize. As a heavier, O-18 water molecule requires more energy than an O-16 water molecule to depart from the liquid state, cooler water releases vapor that is higher in O-16 content. Cooler air precipitates more O-18 than warmer air. Cooler water therefore collects more O-18 relative to O-16 than does warmer water.