The Cretaceous System was first established by Jean Baptiste Julien d'Omalius d'Halloy based on his geological mapping of France and the adjacent areas of the Low Countries and Northern Italy. His map, which was published in 1822, has a legend with a rock unit identified as ‘ Terrain Crétacé ’, and that was the birth of the Cretaceous System that we still use today. Unlike many of the other geological systems, there was no definitive publication. The Cretaceous, as currently defined, occupies the interval of time from 145 to 66 Ma, making it one of the longest in the Phanerozoic. The Cretaceous includes both icehouse and greenhouse (even hothouse) conditions, and much of the time is characterized by exceptionally high sea levels.