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The Cenozoic Era ( ) meaning "new life" is the current and most recent of the three geological eras of the Phanerozoic Eon. The
Cretaceous–Paleogene extinction event near Drumheller, Alberta, where erosion has exposed the K–Pg boundary File:Cretaceous Paleogene clay at Geulhemmergroeve.jpg, alt=Cretaceous Paleogene clay layer with finger pointing to boundary, Complex Cretaceous–Paleogene clay layer (gra ...
(also referred to as the K-Pg, or K-T, extinction event) is the boundary between preceding Mesozoic era and the Cenozoic, which extends from 66 million years ago to the present day. Many species, including all 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
mammal Mammals (from Latin language, Latin , 'breast') are a group of vertebrate animals constituting the class (biology), class Mammalia (), and characterized by the presence of mammary glands which in Female#Mammalian female, females produce milk ...
s – the Eutherians (placentals) in the northern hemisphere and the Metatherians (marsupials, now mainly restricted to Australia) in the southern hemisphere. The extinction of many groups allowed mammals and birds to greatly diversify so that large mammals and birds dominated the Earth. The continents also moved into their current positions during this era. The Earth's climate had begun a drying and cooling trend, culminating in the glaciations of the Pleistocene Epoch, and partially offset by the Paleocene-Eocene Thermal Maximum.


Nomenclature

''Cenozoic,'' meaning "new life," is derived from Greek ''kainós'' "new," and ''zōḗ'' "life." The era is also known as the ''Cænozoic'', ''Caenozoic'', or ''Cainozoic'' (). The name "Cenozoic" (originally: "Kainozoic") was proposed in 1840 by the British geologist
John Phillips
John Phillips
(1800–1874).


Divisions

The Cenozoic is divided into three periods: the
Paleogene The Paleogene ( ; also spelled Palaeogene or Palæogene; informally Lower Tertiary or Early Tertiary) is a geologic period and system that spans 43 million years from the end of the Cretaceous Period million years ago ( Mya) to the beginning o ...
,
Neogene The Neogene ( ) (informally Upper Tertiary or Late Tertiary) is a geologic period and system that spans 20.45 million years from the end of the Paleogene The Paleogene ( ; also spelled Palaeogene or Palæogene; informally Lower Tertiary or E ...
, and
Quaternary Quaternary ( ) is the current and most recent of the three Period (geology), periods of the Cenozoic Era (geology), Era in the geologic time scale of the International Commission on Stratigraphy (ICS). It follows the Neogene Period and spans from ...
; and seven epochs: the
Paleocene The Paleocene, ( ) or Palaeocene, is a geological epoch that lasted from about 66 to 56 million years ago (mya). It is the first epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), Era. The name is a combinatio ...
,
Eocene The Eocene ( ) Epoch is a geological epoch (geology), epoch that lasted from about 56 to 33.9 million years ago (mya). It is the second epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), Era. The name ''Eocene'' ...
,
Oligocene The Oligocene ( ) is a geologic epoch (geology), epoch of the Paleogene Geologic time scale, Period and extends from about 33.9 million to 23 million years before the present ( to ). As with other older geologic periods, the rock beds that define ...
,
Miocene The Miocene ( ) is the first Epoch (geology), geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish author Charles Lyell; its name comes from the Greek words (', "less") and (', "new") and means "le ...
,
Pliocene The Pliocene ( ; also Pleiocene) Epoch is the epoch in the geologic timescale that extends from 5.333 million to 2.58 The common use of epochs during the Cenozoic helps paleontologists better organize and group the many significant events that occurred during this comparatively short interval of time. Knowledge of this era is more detailed than any other era because of the relatively young, well-preserved rocks associated with it.


Paleogene

The Paleogene spans from the extinction of non-avian dinosaurs, 66 million years ago, to the dawn of the Neogene, 23.03 million years ago. It features three epoch (geology), epochs: the
Paleocene The Paleocene, ( ) or Palaeocene, is a geological epoch that lasted from about 66 to 56 million years ago (mya). It is the first epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), Era. The name is a combinatio ...
,
Eocene The Eocene ( ) Epoch is a geological epoch (geology), epoch that lasted from about 56 to 33.9 million years ago (mya). It is the second epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), Era. The name ''Eocene'' ...
and
Oligocene The Oligocene ( ) is a geologic epoch (geology), epoch of the Paleogene Geologic time scale, Period and extends from about 33.9 million to 23 million years before the present ( to ). As with other older geologic periods, the rock beds that define ...
. The Paleocene epoch lasted from 66 million to 56 million years ago. Modern placental mammals originated during this time. The Paleocene is a transitional point between the devastation that is the K–Pg extinction event, and the rich jungle environment that is the Early Eocene. The Early Paleocene saw the recovery of the 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. All known mammals were under 10 kilograms. 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. The temperature was 30 degrees Celsius with little temperature gradient from pole to pole. In the Mid-Eocene, the Circumpolar-Antarctic 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 grass. 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 grass 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.


Neogene

The Neogene spans from 23.03 million to 2.58 million years ago. It features 2 epochs: the Miocene, and the Pliocene. The Miocene epoch spans from 23.03 to 5.333 million years ago and is a period in which grass 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 sea otters. 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, Black, Red Sea, Red, Mediterranean Sea, Mediterranean and Caspian Seas. This increased aridity. Many new plants evolved: 95% of modern Spermatophyte, seed plants evolved in the mid-Miocene. The Pliocene epoch lasted from 5.333 to 2.58 million years ago. The Pliocene featured dramatic climactic changes, which ultimately led to modern species of flora and fauna. The Mediterranean Sea dried up for several million years (because the ice ages reduced sea levels, disconnecting the Atlantic ocean, Atlantic 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, North and South America during the great American interchange, wreaking havoc on local ecologies. Climatic changes brought: savannas that are still continuing to spread across the world; Indian monsoons; deserts 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.


Quaternary

The
Quaternary Quaternary ( ) is the current and most recent of the three Period (geology), periods of the Cenozoic Era (geology), Era in the geologic time scale of the International Commission on Stratigraphy (ICS). It follows the Neogene Period and spans from ...
spans from 2.58 million years ago to present day, and is the shortest geological period in the Phanerozoic Eon. It features modern animals, and dramatic changes in the climate. It is divided into two epochs: the Pleistocene and the Holocene. 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, Sahara, Namib desert, Namib, and Kalahari desert, Kalahari deserts. Many animals evolved including mammoths, giant ground sloths, dire wolves, saber-toothed cats, and most famously ''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 Neanderthals. 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 veterbrate species alone, the majority of which have occurred after 1900.


Animal life

Early in the Cenozoic, following the Cretaceous-Paleogene Extinction Event, K-Pg event, the planet was dominated by relatively small fauna, including small mammals, birds, reptiles, and amphibians. From a geological perspective, it did not take long for mammals and birds to greatly diversify in the absence of the dinosaurs that had dominated during the Mesozoic. Some flightless birds grew larger than humans. These species are sometimes referred to as "terror birds," and were formidable predators. Mammals came to occupy almost every available ecological niche, niche (both marine and terrestrial animal, terrestrial), and some also grew very large, attaining sizes not seen in most of today's terrestrial mammals. Early animals were the Entelodon, Paraceratherium (a hornless rhinoceros relative) and Basilosaurus (an early whale). The extinction of many large diapsid groups, such as the non-avian dinosaurs, Plesiosauria and Pterosauria allowed mammals and birds to greatly diversify and become the world's predominant fauna.


Tectonics

Geology, Geologically, the Cenozoic is the era when the continents moved into their current positions. Australia (continent), Australia-New Guinea, having split from Pangea during the early Cretaceous, drifted north and, eventually, collided with South-east Asia; Antarctica moved into its current position over the South Pole; the Atlantic Ocean widened and, later in the era (2.8 million years ago), South America became attached to North America with the isthmus of Panama. 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, Congo, Niger River, Niger, Nile, Orange River, Orange, Limpopo River, Limpopo and Zambezi River, Zambezi.


Climate

In the Cretaceous, the climate was hot and humid with lush forests at the poles, there was no permanent ice and sea levels were around 300 metres higher than today. This continued for the first 10 million years of the Paleocene, culminating in the Paleocene–Eocene Thermal Maximum about . Around the earth entered a period of long term cooling. This was mainly due to the collision of India with Eurasia, which caused the rise of the Himalayas: the upraised rocks eroded and reacted with in the air, causing a long-term reduction in the proportion of this greenhouse gas in the atmosphere. Around permanent ice began to build up on Antarctica. The cooling trend continued in the
Miocene The Miocene ( ) is the first Epoch (geology), geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish author Charles Lyell; its name comes from the Greek words (', "less") and (', "new") and means "le ...
, with relatively short warmer periods. When South America became attached to North America creating the Isthmus of Panama around , the Arctic region cooled due to the strengthening of the Humboldt Current, Humboldt and Gulf Stream currents, eventually leading to the glaciations of the Quaternary glaciation, Quaternary ice age, the current interglacial of which is the Holocene Epoch. Recent analysis of the geomagnetic reversal frequency, oxygen isotope record, and tectonic plate subduction rate, which are indicators of the changes in the heat flux at the core mantle boundary, climate and plate tectonic activity, shows that all these changes indicate similar rhythms on million years' timescale in the Cenozoic Era occurring with the common fundamental periodicity of ∼13 Myr during most of the time.


Life

During the Cenozoic, Mammal evolution#Expansion of ecological niches in the Mesozoic, mammals proliferated from a few small, simple, generalized forms into a diverse collection of Terrestrial animal, terrestrial, Marine mammal, marine, and bat, flying animals, giving this period its other name, the Age of Mammals. The Cenozoic is just as much the age of savannas, the age of co-dependent flowering plants and insects, and the age of birds. Grass also played a very important role in this era, shaping the evolution of the birds and mammals that fed on it. One group that diversified significantly in the Cenozoic as well were the snakes. Evolving in the Cenozoic, the variety of snakes increased tremendously, resulting in many colubrids, following the evolution of their current primary prey source, the rodents. In the earlier part of the Cenozoic, the world was dominated by the Gastornithidae, gastornithid birds, terrestrial Crocodilia, crocodiles like ''Pristichampsus'', and a handful of primitive large mammal groups like uintatheres, mesonychids, and pantodonts. 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 chalicotheres, creodonts, whales, primates, entelodonts, saber-toothed cats, mastodons and mammoths, three-toed horses, giant rhinoceros like ''Indricotherium'', the rhinoceros-like brontotheres, various bizarre groups of mammals from South America, such as the vaguely elephant-like pyrotheria, pyrotheres and the dog-like marsupial relatives called borhyaenidae, borhyaenids and the monotremes and marsupials of Australia.


See also

* Cretaceous–Paleogene boundary (K–T boundary) * Geologic time scale * Late Cenozoic Ice Age * Mesozoic * Paleozoic * Phanerozoic Eon


References


Bibliography

* ''British Caenozoic Fossils'', 1975, The Natural History Museum, London. * ''Geologic Time'', by Henry Roberts. * ''After the Dinosaurs: The Age of Mammals'', by Donald R. Prothero, Bloomington, Indiana: Indiana University Press, 2006. .


External links


Western Australian Museum – The Age of the Mammals


{{Authority control Cenozoic, Geological eras