Carbon dioxide concentrations have shown several cycles of variation from about 180 parts per million during the deep glaciations of the Holocene and Pleistocene to 280 parts per million during the interglacial periods. Carbon dioxide concentrations have varied widely over the Earth's 4.54 billion year history.
The levels of carbon dioxide in the atmosphere have exhibited periodic shifts in concentration, ranging from about 180 parts per million during the most extreme ice ages of the Holocene and Pleistocene epochs to 280 parts per million during the warmer interglacial periods. The Earth's history has seen a wide range of changes in carbon dioxide concentrations over its 4.54 billion-year existence.