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The Cenozoic Era ( ; ) is Earth's current geological era, representing the last 66million years of Earth's history. It is characterized by the dominance of , Insect, and flowering plant (flowering plants). It is the latest of three geological eras of the Phanerozoic Eon, preceded by the Mesozoic and Paleozoic. The Cenozoic started with the Cretaceous–Paleogene extinction event, when many species, including the non-avian dinosaurs, became extinct in an event attributed by most experts to the impact of a large asteroid or other celestial body, the Chicxulub impactor.
The Cenozoic is also known as the Age of Mammals because the terrestrial animals that dominated both hemispheres were mammalsthe () in the Northern Hemisphere and the (, now mainly restricted to Australia and to some extent South America) in the Southern Hemisphere. The extinction of many groups allowed mammals and birds to greatly diversify so that large mammals and birds dominated life on Earth. The continents also moved into their current positions during this era.
The climate during the early Cenozoic was warmer than today, particularly during the Paleocene–Eocene Thermal Maximum. However, the Eocene to Oligocene transition and the Quaternary glaciation dried and cooled Earth.
In name, the Cenozoic () is comparable to the preceding Mesozoic ('middle life') and Paleozoic ('old life') Eras, as well as to the Proterozoic ('earlier life') Eon.
The Paleocene Epoch lasted from 66 million to 56 million years ago. Modern placental mammals originated during this time. The devastation of the K–Pg extinction event included the extinction of large Herbivore, which permitted the spread of dense but usually species-poor forests. The Early Paleocene saw the recovery of Earth. The continents began to take their modern shape, but all the continents and the subcontinent of India were separated from each other. Afro-Eurasia was separated by the Tethys Sea, and the Americas were separated by the strait of Panama, as the isthmus had not yet formed. This epoch featured a general warming trend, with jungles eventually reaching the poles. The oceans were dominated by sharks as the large reptiles that had once predominated were extinct. Archaic mammals filled the world such as creodonts (extinct carnivores, unrelated to existing Carnivora).
The Eocene Epoch ranged from 56 million years to 33.9 million years ago. In the Early-Eocene, species living in dense forest were unable to evolve into larger forms, as in the Paleocene. Among them were early primates, whales and horses along with many other early forms of mammals. At the top of the food chains were huge birds, such as Paracrax. Carbon dioxide levels were approximately 1,400 ppm. The temperature was 30 degrees Celsius with little temperature gradient from pole to pole. In the Mid-Eocene, the Antarctic Circumpolar Current between Australia and Antarctica formed. This disrupted ocean currents worldwide and as a result caused a global cooling effect, shrinking the jungles. This allowed mammals to grow to mammoth proportions, such as whales which, by that time, had become almost fully aquatic. Mammals like Andrewsarchus were at the top of the food-chain. The Late Eocene saw the rebirth of seasons, which caused the expansion of savanna-like areas, along with the evolution of grasses. The end of the Eocene was marked by the Eocene–Oligocene extinction event, the European face of which is known as the Grande Coupure.
The Oligocene Epoch spans from 33.9 million to 23.03 million years ago. The Oligocene featured the expansion of grasslands which had led to many new species to evolve, including the first elephants, cats, dogs, marsupials and many other species still prevalent today. Many other species of plants evolved in this period too. A cooling period featuring seasonal rains was still in effect. Mammals still continued to grow larger and larger.
The Miocene Epoch spans from 23.03 to 5.333 million years ago and is a period in which grasses spread further, dominating a large portion of the world, at the expense of forests. Kelp forests evolved, encouraging the evolution of new species, such as . During this time, Perissodactyla thrived, and evolved into many different varieties. Apes evolved into 30 species. The Tethys Sea finally closed with the creation of the Arabian Peninsula, leaving only remnants as the Black Sea, Red Sea, Mediterranean and . This increased aridity. Many new plants evolved: 95% of modern Spermatophyte families were present by the end of the Miocene.
The Pliocene Epoch lasted from 5.333 to 2.58 million years ago. The Pliocene featured dramatic climatic changes, which ultimately led to modern species of flora and fauna. The Mediterranean Sea dried up for several million years (because the reduced sea levels, disconnecting the Atlantic Ocean from the Mediterranean, and evaporation rates exceeded inflow from rivers). Australopithecus evolved in Africa, beginning the human branch. The Isthmus of Panama formed, and animals migrated between North America and South America during the great American interchange, wreaking havoc on local ecologies. Climatic changes brought: that are still continuing to spread across the world; Indian ; in central Asia; and the beginnings of the Sahara desert. The world map has not changed much since, save for changes brought about by the glaciations of the Quaternary, such as the Great Lakes, Hudson Bay, and the Baltic Sea.
The Pleistocene lasted from 2.58 million to 11,700 years ago. This epoch was marked by ice ages as a result of the cooling trend that started in the Mid-Eocene. There were at least four separate glaciation periods marked by the advance of ice caps as far south as 40° N in mountainous areas. Meanwhile, Africa experienced a trend of desiccation which resulted in the creation of the Sahara desert, Namib Desert, and Kalahari Desert deserts. Many animals evolved including , giant ground sloths, dire wolves, sabre-toothed cats, and Homo sapiens. 100,000 years ago marked the end of one of the worst droughts in Africa, and led to the expansion of primitive humans. As the Pleistocene drew to a close, a major extinction wiped out much of the world's megafauna, including some of the hominid species, such as . All the continents were affected, but Africa to a lesser extent. It still retains many large animals, such as hippos.
The Holocene began 11,700 years ago and lasts to the present day. All recorded history and "the Human history" lies within the boundaries of the Holocene Epoch. Human activity is blamed for a mass extinction that began roughly 10,000 years ago, though the species becoming extinct have only been recorded since the Industrial Revolution. This is sometimes referred to as the "Sixth Extinction". It is often cited that over 322 recorded species have become extinct due to human activity since the Industrial Revolution, but the rate may be as high as 500 vertebrate species alone, the majority of which have occurred after 1900.
India collided with Asia creating the Himalayas; Arabia collided with Eurasia, closing the Tethys Ocean and creating the Zagros Mountains, around .
The break-up of Gondwana in Late Cretaceous and Cenozoic times led to a shift in the river courses of various large African rivers including the Congo River, Niger River, Nile, Orange River, Limpopo River and Zambezi River.
During the Cenozoic, mammals proliferated from a few small, simple, generalised forms into a diverse collection of terrestrial, Marine mammal, and bat animals, giving this period its other name, the Age of Mammals. The Cenozoic is just as much the age of , the age of co-dependent and , and the age of birds. Grasses also played a very important role in this era, shaping the evolution of the birds and mammals that fed on them. One group that diversified significantly in the Cenozoic as well were the . Evolving in the Cenozoic, the variety of snakes increased tremendously, resulting in many colubrids, following the evolution of their current primary prey source, the .
In the earlier part of the Cenozoic, the world was dominated by the Gastornithidae birds, terrestrial like Pristichampsus, large sharks such as Otodus, and a handful of primitive large mammal groups like , Mesonychia, and . But as the forests began to recede and the climate began to cool, other mammals took over.
The Cenozoic is full of mammals both strange and familiar, including , , , , , sabre-toothed cats, and , , giant rhinoceros like Paraceratherium, the rhinoceros-like , various bizarre groups of mammals from South America, such as the vaguely elephant-like pyrotheria and the dog-like marsupial relatives called borhyaenidae and the and marsupials of Australia. Mammal evolution in the Cenozoic was predominantly shaped by climatic and geological processes.
Cenozoic calcareous nannoplankton experienced rapid rates of speciation and reduced species longevity, while suffering prolonged declines in diversity during the Eocene and Neogene. Diatom, in contrast, experienced major diversification over the Eocene, especially at high latitudes, as the world's oceans cooled. Diatom diversification was particularly concentrated at the Eocene-Oligocene boundary. A second major pulse of diatom diversification occurred over the course of the Middle and Late Miocene.
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