Paleoclimatology is the study of prehistoric climates. Records of past climates are found in sedimentary rocks, in cores taken through
deep layers of ice, and in fossil-bearing
cores from the beds of seas and lakes. From such evidence, climatologists
have discovered that the Earth is subject to alternate periods of cold,
called glacials or ice ages, and warmth, called interglacials. During the
last two million years there have been 17 ice ages.
|The present-day formations of preservable climate-related
features are shown. The foraminiferan Globorotalia is an
indicator of sea temperature. It coils right in warm waters and left
in cold waters. Corals reefs and major carbonate deposits are both
typical of warm, shallow seas. Common to desert environments are evaporate
deposits (salt basins) and reddish-hued sandstones. The lush plant
life of tropical forests and swamps is the raw material from which
coal is formed. Ice sheets groove and scratch the face of rocks and
leave characteristic deposits of glacial till, and peat bogs are typical
of the tundra environment along the fringes of the ice caps.