Cenozoic

Cenozoic. The Cenozoic is the current and most recent of the three major geological eras of the Phanerozoic Eon, following the Mesozoic and spanning from about 66 million years ago to the present. Often called the "Age of Mammals," it is characterized by the dramatic diversification and ecological dominance of mammals, birds, and flowering plants, as well as the profound cooling of the global climate culminating in the Quaternary glaciation. The era witnessed the final breakup of the supercontinent Gondwana, the rise of the Alpine-Himalayan mountain belt, and the evolution and global impact of the genus Homo.

Etymology and definition

The term "Cenozoic" derives from the Greek words *kainos* (new) and *zoe* (life), meaning "new life," a name coined in the 19th century to reflect the modern fauna and flora that emerged following the Cretaceous–Paleogene extinction event. It was formally defined in 1841 by the British geologist John Phillips, who divided the Phanerozoic into three eras. The base of the Cenozoic is formally defined at the Global Boundary Stratotype Section and Point (GSSP) for the Danian stage at El Kef in Tunisia, which marks the iridium-rich layer associated with the Chicxulub impactor asteroid impact.

Major subdivisions

The Cenozoic is divided into three periods: the Paleogene, Neogene, and Quaternary. The Paleogene (66–23 million years ago) comprises the Paleocene, Eocene, and Oligocene epochs and encompasses the initial recovery of ecosystems and the rise of modern mammalian orders. The Neogene (23–2.6 million years ago) includes the Miocene and Pliocene epochs, a time of further climatic cooling and the spread of grasslands. The Quaternary (2.6 million years ago to present) consists of the Pleistocene and Holocene epochs and is defined by cyclical glaciations and the evolution of humans.

Tectonics and paleogeography

The paleogeography of this era was shaped by the continued dispersal of continents following the breakup of Pangaea. Major events included the final separation of South America from Antarctica, the opening of the Drake Passage, and the northward movement of the Indian subcontinent culminating in its collision with Eurasia to form the Himalayas and the Tibetan Plateau. The closure of the Tethys Ocean and the collision of Africa with Europe created the Alps, while the subduction of the Farallon Plate beneath North America formed the Rocky Mountains and the Sierra Nevada.

Climate and life

The early part of the era, particularly the Paleocene–Eocene Thermal Maximum, was a period of extreme global warmth with lush forests extending to the poles. This greenhouse world supported archaic mammals like creodonts and condylarths. A long-term cooling trend began in the Eocene, driven by declining atmospheric carbon dioxide levels and the tectonic uplift of the Himalayas and the Andes, which enhanced silicate weathering. The establishment of the Antarctic Circumpolar Current after the opening of the Drake Passage led to the glaciation of Antarctica by the Oligocene.

Cenozoic recovery and diversification

In the wake of the extinction of non-avian dinosaurs and large marine reptiles, mammals rapidly diversified to fill vacant ecological niches. Key evolutionary events included the appearance of the first primates, cetaceans, and perissodactyls like horses and rhinos during the Eocene. The spread of open grasslands in the Miocene, facilitated by global cooling and drying, drove the evolution of fast-running ungulates like equids and predatory canids. This period also saw the remarkable diversification of songbirds and the global expansion of C4 photosynthesis in grasses.

Human evolution and impact

The late Cenozoic witnessed the evolution of the hominin lineage in Africa, with key genera including Australopithecus, Paranthropus, and Homo. The development of Oldowan and Acheulean tool technologies by early members of the genus Homo marked a significant cognitive leap. The migration of Homo erectus out of Africa into Eurasia was a major biogeographic event. The emergence of Homo sapiens in the Late Pleistocene and their subsequent global dispersal, coupled with the development of agriculture during the Holocene, has fundamentally reshaped the biosphere, leading to the proposed current geological epoch defined by human activity. Category:Geological eras Category:Cenozoic