Recently, ice-core data have confirmed this scenario. Ice
retains the same chemical properties that were present when the snow fell and
it is possible to distinguish years similarly to the rings in a tree trunk. Air
bubbles trapped in ice rings are used to determine the variations of methane,
carbon dioxide, temperature and dust due to volcanic eruptions. Antarcticas
ice cores allow to reconstruct temperatures, carbon dioxide and atmospheric
composition, for the entire Quaternary period.
The Vital Needs Theory - page 93