The Cenozoic era (the era of "recent life") is the third era of the Phanerozoic Eon, or period of visible multicellular life, which followed the Precambrian time in Earth history. The Cenozoic era, which is the current era of Earth history, began with the mass extinction event that occurred at the end of the Cretaceous period of the Mesozoic era. The Cenozoic era is traditionally divided into two geological periods, the Tertiary period and the Quaternary period.

The Cretaceous extinction left a world in which many organisms had died and much space and many resources were available for growth. The dinosaurs had become extinct, as well as numerous lineages within the birds, reptiles, and mammals. The conifers that had dominated the early Mesozoic forests came to dominate only the forests of cold or nutrient-poor mountainous regions in the Cenozoic. The flowering plants evolved in the Cretaceous period but proliferated during the Cenozoic era, into the forest trees that dominate the temperate and tropical regions, and many shrubs and herbaceous species. The explosive speciation of flowering plants paralleled that of insect groups such as bees, butterflies, and flies, a pattern most scientists attribute to coevolution.

The Cenozoic world was cooler and drier than most of previous Earth history. Climatic conditions became cooler and drier during the late Cenozoic than they had been early in the Cenozoic. During the middle of the Tertiary period, dry conditions allowed the adaptation of grasses and other plants to aridity, and the spread of grasslands and deserts. Grazing animals evolved from browsing ancestors, taking advantage of the grass food base. Five million years ago, the Mediterranean dried up into a salt flat. The coolest and driest conditions began with the Quaternary period. About every hundred thousand years, glaciers build up around the Arctic Ocean and push southward over the northern continents. Meanwhile, lower sea levels and reduced evaporation result in drier conditions in the equatorial regions. . .

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