The sequence of climatic changes in geologic time. It shows a succession of oscillations between warm periods and ice ages, but superimposed on this are numerous shorter oscillations. The tendency to regard the whole of a geologic period, lasting for 20 million years and more, as having a single type of climate is a great oversimplification, as is shown by the succession of glacial and interglacial periods in the Quaternary. Even the warm periods are known to have been made up of successions of climates of different degrees of warmth; but until much more information is available, it will not be possible to set out in detail the sequence of changes of the earlier paleoclimates.