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In the middle of the Cretaceous period the climatic zonation of the Earth differed from the present zonation. During that time, the polar regions were free from permanent glaciation and permafrost. Episodic glacial deposits of the Middle Cretaceous indicate only short cooling periods, which locally resulted in the seasonal freezing of seas. The temperate character of the high-latitude climate is evident from the composition of Middle Cretaceous vegetation and intense coal accumulation as well as occurrences of thermophilic insects and dinosaurs. Accordingly, this peculiar climate of the mid-Cretaceous was of the temperate, high-latitude type. It had distinct seasonal variations in insolation and temperature conditions that changed from moderately cool to moderately warm (polar nights and days). As indicated by the types of vegetation; thermophilic insects; abundant dinosaurs; and the widespread distribution of laterite, bauxite, kaolin, and coal deposits, the conditions in the middle latitudes of both hemispheres corresponded to a warm humid climate. Arid belts were also typical of the mid-Cretaceous Earth. During the Aptian, they occupied nearly all of the low-latitude zones and some provinces within the middle latitudes. In subequatorial zones, traces of the humid Aptian climate are episodic and occur only in the northeastern Arabian plate. The humid climatic belt near the equator was formed later, during the Albian-Turonian interval; it was confined to the western Gondwanan continents only. Its appearance seems to be related to the opening of the South Atlantic Ocean.