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
mammal
A mammal () is a vertebrate animal of the Class (biology), class Mammalia (). Mammals are characterised by the presence of milk-producing mammary glands for feeding their young, a broad neocortex region of the brain, fur or hair, and three ...
s,
insects
Insects (from Latin ') are hexapod invertebrates of the class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body (head, thorax and abdomen), three pairs of jointed ...
,
bird
Birds are a group of warm-blooded vertebrates constituting the class (biology), class Aves (), characterised by feathers, toothless beaked jaws, the Oviparity, laying of Eggshell, hard-shelled eggs, a high Metabolism, metabolic rate, a fou ...
s and
angiosperm
Flowering plants are plants that bear flowers and fruits, and form the clade Angiospermae (). The term angiosperm is derived from the Greek words (; 'container, vessel') and (; 'seed'), meaning that the seeds are enclosed within a fruit ...
s (flowering plants). It is the latest of three geological eras of the
Phanerozoic Eon, preceded by the
Mesozoic
The Mesozoic Era is the Era (geology), era of Earth's Geologic time scale, geological history, lasting from about , comprising the Triassic, Jurassic and Cretaceous Period (geology), Periods. It is characterized by the dominance of archosaurian r ...
and
Paleozoic
The Paleozoic ( , , ; or Palaeozoic) Era is the first of three Era (geology), geological eras of the Phanerozoic Eon. Beginning 538.8 million years ago (Ma), it succeeds the Neoproterozoic (the last era of the Proterozoic Eon) and ends 251.9 Ma a ...
. The Cenozoic started with the
Cretaceous–Paleogene extinction event
The Cretaceous–Paleogene (K–Pg) extinction event, also known as the K–T extinction, was the extinction event, mass extinction of three-quarters of the plant and animal species on Earth approximately 66 million years ago. The event cau ...
, 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
eutheria
Eutheria (from Greek , 'good, right' and , 'beast'; ), also called Pan-Placentalia, is the clade consisting of Placentalia, placental mammals and all therian mammals that are more closely related to placentals than to marsupials.
Eutherians ...
ns (
placentals) in the Northern Hemisphere and the
metatheria
Metatheria is a mammalian clade that includes all mammals more closely related to marsupials than to placentals. First proposed by Thomas Henry Huxley in 1880, it is a more inclusive group than the marsupials; it contains all marsupials as wel ...
ns (
marsupial
Marsupials are a diverse group of mammals belonging to the infraclass Marsupialia. They are natively found in Australasia, Wallacea, and the Americas. One of marsupials' unique features is their reproductive strategy: the young are born in a r ...
s, now mainly restricted to
Australia
Australia, officially the Commonwealth of Australia, is a country comprising mainland Australia, the mainland of the Australia (continent), Australian continent, the island of Tasmania and list of islands of Australia, numerous smaller isl ...
and to some extent
South America
South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a considerably smaller portion in the Northern Hemisphere. It can also be described as the southern Subregion#Americas, subregion o ...
) 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
The Paleocene–Eocene thermal maximum (PETM), alternatively ”Eocene thermal maximum 1 (ETM1)“ and formerly known as the "Initial Eocene" or “Late Paleocene thermal maximum", was a geologically brief time interval characterized by a ...
. However, the
Eocene
The Eocene ( ) is a geological epoch (geology), epoch that lasted from about 56 to 33.9 million years ago (Ma). It is the second epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), Era. The name ''Eocene'' comes ...
to
Oligocene
The Oligocene ( ) is a geologic epoch (geology), epoch of the Paleogene Geologic time scale, Period that extends from about 33.9 million to 23 million years before the present ( to ). As with other older geologic periods, the rock beds that defin ...
transition and the
Quaternary glaciation
The Quaternary glaciation, also known as the Pleistocene glaciation, is an alternating series of glacial period, glacial and interglacial, interglacial periods during the Quaternary period that began 2.58 Year#SI prefix multipliers, Ma (million ...
dried and cooled Earth.
Nomenclature
''Cenozoic'' derives from the
Ancient Greek
Ancient Greek (, ; ) includes the forms of the Greek language used in ancient Greece and the classical antiquity, ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Mycenaean Greek (), Greek ...
words (, 'new') and (, 'life').
The name was proposed in 1840 by the British geologist
John Phillips (1800–1874), who originally spelled it ''Kainozoic''. The era is also known as the ''Cænozoic'', ''Caenozoic'', or ''Cainozoic'' ().
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.
Divisions
The Cenozoic is divided into three periods: the
Paleogene
The Paleogene Period ( ; also spelled Palaeogene or Palæogene) is a geologic period and system that spans 43 million years from the end of the Cretaceous Period Ma (million years ago) to the beginning of the Neogene Period Ma. It is the fir ...
,
Neogene
The Neogene ( ,) is a geologic period and system that spans 20.45 million years from the end of the Paleogene Period million years ago ( Mya) to the beginning of the present Quaternary Period million years ago. It is the second period of th ...
, and
Quaternary
The Quaternary ( ) is the current and most recent of the three periods of the Cenozoic Era in the geologic time scale of the International Commission on Stratigraphy (ICS), as well as the current and most recent of the twelve periods of the ...
; and seven
epoch
In chronology and periodization, an epoch or reference epoch is an instant in time chosen as the origin of a particular calendar era. The "epoch" serves as a reference point from which time is measured.
The moment of epoch is usually decided b ...
s: the
Paleocene
The Paleocene ( ), or Palaeocene, is a geological epoch (geology), epoch that lasted from about 66 to 56 mya (unit), million years ago (mya). It is the first epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), ...
,
Eocene
The Eocene ( ) is a geological epoch (geology), epoch that lasted from about 56 to 33.9 million years ago (Ma). It is the second epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), Era. The name ''Eocene'' comes ...
,
Oligocene
The Oligocene ( ) is a geologic epoch (geology), epoch of the Paleogene Geologic time scale, Period that extends from about 33.9 million to 23 million years before the present ( to ). As with other older geologic periods, the rock beds that defin ...
,
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 geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and mea ...
,
Pliocene
The Pliocene ( ; also Pleiocene) is the epoch (geology), epoch in the geologic time scale that extends from 5.33 to 2.58[Pleistocene
The Pleistocene ( ; referred to colloquially as the ''ice age, Ice Age'') is the geological epoch (geology), epoch that lasted from to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was fin ...](_blank)
, and
Holocene
The Holocene () is the current geologic time scale, geological epoch, beginning approximately 11,700 years ago. It follows the Last Glacial Period, which concluded with the Holocene glacial retreat. The Holocene and the preceding Pleistocene to ...
. The Quaternary Period was officially recognised by the
International Commission on Stratigraphy
The International Commission on Stratigraphy (ICS), sometimes unofficially referred to as the International Stratigraphic Commission, is a daughter or major subcommittee grade scientific organization that concerns itself with stratigraphy, strati ...
in June 2009.
In 2004, the
Tertiary Period
The Tertiary ( ) is an obsolete Period (geology), geologic period spanning 66 million to 2.6 or 1.8 million years ago. The period began with the extinction of the non-bird, avian dinosaurs in the Cretaceous–Paleogene extinction event, at t ...
was officially replaced by the Paleogene and Neogene Periods. The common use of epochs during the Cenozoic helps
palaeontologist
Paleontology, also spelled as palaeontology or palæontology, is the scientific study of the life of the past, mainly but not exclusively through the study of fossils. Paleontologists use fossils as a means to classify organisms, measure geolo ...
s better organise 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
The Paleogene Period ( ; also spelled Palaeogene or Palæogene) is a geologic period and system that spans 43 million years from the end of the Cretaceous Period Ma (million years ago) to the beginning of the Neogene Period Ma. It is the fir ...
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
In chronology and periodization, an epoch or reference epoch is an instant in time chosen as the origin of a particular calendar era. The "epoch" serves as a reference point from which time is measured.
The moment of epoch is usually decided b ...
s: the
Paleocene
The Paleocene ( ), or Palaeocene, is a geological epoch (geology), epoch that lasted from about 66 to 56 mya (unit), million years ago (mya). It is the first epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), ...
,
Eocene
The Eocene ( ) is a geological epoch (geology), epoch that lasted from about 56 to 33.9 million years ago (Ma). It is the second epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), Era. The name ''Eocene'' comes ...
and
Oligocene
The Oligocene ( ) is a geologic epoch (geology), epoch of the Paleogene Geologic time scale, Period that extends from about 33.9 million to 23 million years before the present ( to ). As with other older geologic periods, the rock beds that defin ...
.

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
herbivores, 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
Afro-Eurasia (also Afroeurasia and Eurafrasia) is a landmass comprising the continents of Africa, Asia, and Europe. The terms are compound (linguistics), compound words of the names of its constituent parts. Afro-Eurasia has also been called th ...
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
''Andrewsarchus'' (), meaning "Roy Chapman Andrews, Andrews' ruler", is an extinct genus of artiodactyl that lived during the Eocene, Middle Eocene in what is now China. The genus was species description, first described by Henry Fairfield Osb ...
'' 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.
Neogene
The
Neogene
The Neogene ( ,) is a geologic period and system that spans 20.45 million years from the end of the Paleogene Period million years ago ( Mya) to the beginning of the present Quaternary Period million years ago. It is the second period of th ...
spans from 23.03 million to 2.58 million years ago. It features two 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
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
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
The Arabian Peninsula (, , or , , ) or Arabia, is a peninsula in West Asia, situated north-east of Africa on the Arabian plate. At , comparable in size to India, the Arabian Peninsula is the largest peninsula in the world.
Geographically, the ...
, leaving only remnants as the
Black
Black is a color that results from the absence or complete absorption of visible light. It is an achromatic color, without chroma, like white and grey. It is often used symbolically or figuratively to represent darkness.Eva Heller, ''P ...
,
Red,
Mediterranean
The Mediterranean Sea ( ) is a sea connected to the Atlantic Ocean, surrounded by the Mediterranean basin and almost completely enclosed by land: on the east by the Levant in West Asia, on the north by Anatolia in West Asia and Southern ...
and
Caspian Sea
The Caspian Sea is the world's largest inland body of water, described as the List of lakes by area, world's largest lake and usually referred to as a full-fledged sea. An endorheic basin, it lies between Europe and Asia: east of the Caucasus, ...
s. This increased aridity. Many new plants evolved: 95% of modern
seed plants 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
ice age
An ice age is a long period of reduction in the temperature of Earth's surface and atmosphere, resulting in the presence or expansion of continental and polar ice sheets and alpine glaciers. Earth's climate alternates between ice ages, and g ...
s reduced sea levels, disconnecting the
Atlantic from the Mediterranean, and evaporation rates exceeded inflow from rivers). ''
Australopithecus
''Australopithecus'' (, ; or (, ) is a genus of early hominins that existed in Africa during the Pliocene and Early Pleistocene. The genera ''Homo'' (which includes modern humans), ''Paranthropus'', and ''Kenyanthropus'' evolved from some ''Aus ...
'' evolved in
Africa
Africa is the world's second-largest and second-most populous continent after Asia. At about 30.3 million km2 (11.7 million square miles) including adjacent islands, it covers 20% of Earth's land area and 6% of its total surfac ...
, beginning the human branch. The
Isthmus of Panama
The Isthmus of Panama, historically known as the Isthmus of Darien, is the narrow strip of land that lies between the Caribbean Sea and the Pacific Ocean, linking North America, North and South America. The country of Panama is located on the i ...
formed, and animals migrated between
North
North is one of the four compass points or cardinal directions. It is the opposite of south and is perpendicular to east and west. ''North'' is a noun, adjective, or adverb indicating Direction (geometry), direction or geography.
Etymology
T ...
and
South America
South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a considerably smaller portion in the Northern Hemisphere. It can also be described as the southern Subregion#Americas, subregion o ...
during the
great American interchange
The Great American Biotic Interchange (commonly abbreviated as GABI), also known as the Great American Interchange and the Great American Faunal Interchange, was an important late Cenozoic paleozoogeographic biotic interchange event in which land ...
, wreaking havoc on local ecologies. Climatic changes brought:
savanna
A savanna or savannah is a mixed woodland-grassland (i.e. grassy woodland) biome and ecosystem characterised by the trees being sufficiently widely spaced so that the canopy does not close. The open canopy allows sufficient light to reach th ...
s that are still continuing to spread across the world; Indian
monsoon
A monsoon () is traditionally a seasonal reversing wind accompanied by corresponding changes in precipitation but is now used to describe seasonal changes in Atmosphere of Earth, atmospheric circulation and precipitation associated with annu ...
s;
desert
A desert is a landscape where little precipitation occurs and, consequently, living conditions create unique biomes and ecosystems. The lack of vegetation exposes the unprotected surface of the ground to denudation. About one-third of the la ...
s in central
Asia
Asia ( , ) is the largest continent in the world by both land area and population. It covers an area of more than 44 million square kilometres, about 30% of Earth's total land area and 8% of Earth's total surface area. The continent, which ...
; and the beginnings of the
Sahara
The Sahara (, ) is a desert spanning across North Africa. With an area of , it is the largest hot desert in the world and the list of deserts by area, third-largest desert overall, smaller only than the deserts of Antarctica and the northern Ar ...
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
The Great Lakes, also called the Great Lakes of North America, are a series of large interconnected freshwater lakes spanning the Canada–United States border. The five lakes are Lake Superior, Superior, Lake Michigan, Michigan, Lake Huron, H ...
,
Hudson Bay
Hudson Bay, sometimes called Hudson's Bay (usually historically), is a large body of Saline water, saltwater in northeastern Canada with a surface area of . It is located north of Ontario, west of Quebec, northeast of Manitoba, and southeast o ...
, and the
Baltic Sea
The Baltic Sea is an arm of the Atlantic Ocean that is enclosed by the countries of Denmark, Estonia, Finland, Germany, Latvia, Lithuania, Poland, Russia, Sweden, and the North European Plain, North and Central European Plain regions. It is the ...
.
Quaternary
The
Quaternary
The Quaternary ( ) is the current and most recent of the three periods of the Cenozoic Era in the geologic time scale of the International Commission on Stratigraphy (ICS), as well as the current and most recent of the twelve periods of the ...
spans from 2.58 million years ago to present day, and is the shortest geological period in the
Phanerozoic Eon
The Phanerozoic is the current and the latest of the four geologic eons in the Earth's geologic time scale, covering the time period from 538.8 million years ago to the present. It is the eon during which abundant animal and plant life has ...
. It features modern animals, and dramatic changes in the climate. It is divided into two epochs: the Pleistocene and the Holocene.
The
Pleistocene
The Pleistocene ( ; referred to colloquially as the ''ice age, Ice Age'') is the geological epoch (geology), epoch that lasted from to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was fin ...
lasted from 2.58 million to 11,700 years ago. This epoch was marked by
ice ages
An ice age is a long period of reduction in the temperature of Earth's surface and atmosphere, resulting in the presence or expansion of continental and polar ice sheets and alpine glaciers. Earth's climate alternates between ice ages, and Gre ...
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
Desiccation is the state of extreme dryness, or the process of extreme drying. A desiccant is a hygroscopic (attracts and holds water) substance that induces or sustains such a state in its local vicinity in a moderately sealed container. The ...
which resulted in the creation of the
Sahara
The Sahara (, ) is a desert spanning across North Africa. With an area of , it is the largest hot desert in the world and the list of deserts by area, third-largest desert overall, smaller only than the deserts of Antarctica and the northern Ar ...
,
Namib
The Namib ( ; ) is a coastal desert in Southern Africa. According to the broadest definition, the Namib stretches for more than along the Atlantic coasts of Angola, Namibia, and northwest South Africa, extending southward from the Carunjamba Ri ...
, and
Kalahari
The Kalahari Desert is a large semiarid sandy savanna in Southern Africa covering including much of Botswana as well as parts of Namibia and South Africa.
It is not to be confused with the Angolan, Namibian, and South African Namib coastal d ...
deserts. Many animals evolved including
mammoth
A mammoth is any species of the extinct elephantid genus ''Mammuthus.'' They lived from the late Miocene epoch (from around 6.2 million years ago) into the Holocene until about 4,000 years ago, with mammoth species at various times inhabi ...
s,
giant ground sloths,
dire wolves, sabre-toothed cats, and ''
Homo sapiens
Humans (''Homo sapiens'') or modern humans are the most common and widespread species of primate, and the last surviving species of the genus ''Homo''. They are Hominidae, great apes characterized by their Prehistory of nakedness and clothing ...
''. 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
Neanderthal
Neanderthals ( ; ''Homo neanderthalensis'' or sometimes ''H. sapiens neanderthalensis'') are an extinction, extinct group of archaic humans who inhabited Europe and Western and Central Asia during the Middle Pleistocene, Middle to Late Plei ...
s. All the continents were affected, but Africa to a lesser extent. It still retains many large animals, such as hippos.
The
Holocene
The Holocene () is the current geologic time scale, geological epoch, beginning approximately 11,700 years ago. It follows the Last Glacial Period, which concluded with the Holocene glacial retreat. The Holocene and the preceding Pleistocene to ...
began 11,700 years ago and lasts to the present day. All recorded history and "the
Human history
Human history or world history is the record of humankind from prehistory to the present. Early modern human, Modern humans evolved in Africa around 300,000 years ago and initially lived as hunter-gatherers. They Early expansions of hominin ...
" 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
The Industrial Revolution, sometimes divided into the First Industrial Revolution and Second Industrial Revolution, was a transitional period of the global economy toward more widespread, efficient and stable manufacturing processes, succee ...
. This is sometimes referred to as the "
Sixth Extinction
The Holocene extinction, also referred to as the Anthropocene extinction or the sixth mass extinction, is an ongoing extinction event caused exclusively by human activities during the Holocene epoch. This extinction event spans numerous families ...
". 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.
Tectonics
Geologically, the Cenozoic is the era when the
continent
A continent is any of several large geographical regions. Continents are generally identified by convention (norm), convention rather than any strict criteria. A continent could be a single large landmass, a part of a very large landmass, as ...
s moved into their current positions.
Australia-New Guinea, having split from
Pangea
Pangaea or Pangea ( ) was a supercontinent that existed during the late Paleozoic and early Mesozoic eras. It assembled from the earlier continental units of Gondwana, Euramerica and Siberia (continent), Siberia during the Carboniferous period ...
during the early
Cretaceous
The Cretaceous ( ) is a geological period that lasted from about 143.1 to 66 mya (unit), million years ago (Mya). It is the third and final period of the Mesozoic Era (geology), Era, as well as the longest. At around 77.1 million years, it is the ...
, drifted north and, eventually, collided with
Southeast Asia
Southeast Asia is the geographical United Nations geoscheme for Asia#South-eastern Asia, southeastern region of Asia, consisting of the regions that are situated south of China, east of the Indian subcontinent, and northwest of the Mainland Au ...
;
Antarctica
Antarctica () is Earth's southernmost and least-populated continent. Situated almost entirely south of the Antarctic Circle and surrounded by the Southern Ocean (also known as the Antarctic Ocean), it contains the geographic South Pole. ...
moved into its current position over the
South Pole
The South Pole, also known as the Geographic South Pole or Terrestrial South Pole, is the point in the Southern Hemisphere where the Earth's rotation, Earth's axis of rotation meets its surface. It is called the True South Pole to distinguish ...
; the
Atlantic Ocean
The Atlantic Ocean is the second largest of the world's five borders of the oceans, oceanic divisions, with an area of about . It covers approximately 17% of Earth#Surface, Earth's surface and about 24% of its water surface area. During the ...
widened and, later in the era (2.8 million years ago),
South America
South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a considerably smaller portion in the Northern Hemisphere. It can also be described as the southern Subregion#Americas, subregion o ...
became attached to
North America
North America is a continent in the Northern Hemisphere, Northern and Western Hemisphere, Western hemispheres. North America is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South Ameri ...
with the
isthmus of Panama
The Isthmus of Panama, historically known as the Isthmus of Darien, is the narrow strip of land that lies between the Caribbean Sea and the Pacific Ocean, linking North America, North and South America. The country of Panama is located on the i ...
.
India collided with Asia creating the Himalayas; Arabia collided with Eurasia, closing the
Tethys Ocean
The Tethys Ocean ( ; ), also called the Tethys Sea or the Neo-Tethys, was a prehistoric ocean during much of the Mesozoic Era and early-mid Cenozoic Era. It was the predecessor to the modern Indian Ocean, the Mediterranean Sea, and the Eurasia ...
and creating the
Zagros Mountains
The Zagros Mountains are a mountain range in Iran, northern Iraq, and southeastern Turkey. The mountain range has a total length of . The Zagros range begins in northwestern Iran and roughly follows Iran's western border while covering much of s ...
, around .
The break-up of Gondwana in
Late Cretaceous
The Late Cretaceous (100.5–66 Ma) is the more recent of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''cre ...
and Cenozoic times led to a shift in the river courses of various large African rivers including the
Congo,
Niger
Niger, officially the Republic of the Niger, is a landlocked country in West Africa. It is a unitary state Geography of Niger#Political geography, bordered by Libya to the Libya–Niger border, north-east, Chad to the Chad–Niger border, east ...
,
Nile
The Nile (also known as the Nile River or River Nile) is a major north-flowing river in northeastern Africa. It flows into the Mediterranean Sea. The Nile is the longest river in Africa. It has historically been considered the List of river sy ...
,
Orange,
Limpopo
Limpopo () is the northernmost Provinces of South Africa, province of South Africa. It is named after the Limpopo River, which forms the province's western and northern borders. The term Limpopo is derived from Rivombo (Livombo/Lebombo), a ...
and
Zambezi
The Zambezi (also spelled Zambeze and Zambesi) is the fourth-longest river in Africa, the longest east-flowing river in Africa and the largest flowing into the Indian Ocean from Africa. Its drainage basin covers , slightly less than half of t ...
.
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
The Paleocene–Eocene thermal maximum (PETM), alternatively ”Eocene thermal maximum 1 (ETM1)“ and formerly known as the "Initial Eocene" or “Late Paleocene thermal maximum", was a geologically brief time interval characterized by a ...
about . Around , 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 Himalayas, or Himalaya ( ), is a mountain range in Asia, separating the plains of the Indian subcontinent from the Tibetan Plateau. The range has some of the Earth's highest peaks, including the highest, Mount Everest. More than list of h ...
: 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 geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and mea ...
, with relatively short warmer periods. When South America became attached to North America creating the
Isthmus of Panama
The Isthmus of Panama, historically known as the Isthmus of Darien, is the narrow strip of land that lies between the Caribbean Sea and the Pacific Ocean, linking North America, North and South America. The country of Panama is located on the i ...
around , the Arctic region cooled due to the strengthening of the
Humboldt and
Gulf Stream
The Gulf Stream is a warm and swift Atlantic ocean current that originates in the Gulf of Mexico and flows through the Straits of Florida and up the eastern coastline of the United States, then veers east near 36°N latitude (North Carolin ...
currents, eventually leading to the glaciations of the
Quaternary ice age
The Quaternary glaciation, also known as the Pleistocene glaciation, is an alternating series of glacial and interglacial periods during the Quaternary period that began 2.58 Ma (million years ago) and is ongoing. Although geologists describe ...
, the current
interglacial
An interglacial period (or alternatively interglacial, interglaciation) is a geological interval of warmer global average temperature lasting thousands of years that separates consecutive glacial periods within an ice age. The current Holocene i ...
of which is the
Holocene
The Holocene () is the current geologic time scale, geological epoch, beginning approximately 11,700 years ago. It follows the Last Glacial Period, which concluded with the Holocene glacial retreat. The Holocene and the preceding Pleistocene to ...
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. The levels of carbonate ions in the ocean fell over the course of the Cenozoic.
Life

Early in the Cenozoic, following the
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 to greatly diversify in the absence of the dinosaurs that had dominated during the Mesozoic. Birds also diversified rapidly; 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
niche (both marine and
terrestrial), and some also grew very large, attaining sizes not seen in most of today's terrestrial mammals. The ranges of many Cenozoic bird clades were governed by latitude and temperature and have contracted over the course of this era as the world cooled.
During the Cenozoic,
mammals proliferated from a few small, simple, generalised forms into a diverse collection of
terrestrial,
marine, and
flying animals, giving this period its other name, the Age of Mammals. The Cenozoic is just as much the age of
savanna
A savanna or savannah is a mixed woodland-grassland (i.e. grassy woodland) biome and ecosystem characterised by the trees being sufficiently widely spaced so that the canopy does not close. The open canopy allows sufficient light to reach th ...
s, the age of co-dependent
flowering plant
Flowering plants are plants that bear flowers and fruits, and form the clade Angiospermae (). The term angiosperm is derived from the Ancient Greek, Greek words (; 'container, vessel') and (; 'seed'), meaning that the seeds are enclosed with ...
s and
insect
Insects (from Latin ') are Hexapoda, hexapod invertebrates of the class (biology), class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body (Insect morphology#Head, head, ...
s, 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
snake
Snakes are elongated limbless reptiles of the suborder Serpentes (). Cladistically squamates, snakes are ectothermic, amniote vertebrates covered in overlapping scales much like other members of the group. Many species of snakes have s ...
s. Evolving in the Cenozoic, the variety of snakes increased tremendously, resulting in many
colubrids, following the evolution of their current primary prey source, the
rodent
Rodents (from Latin , 'to gnaw') are mammals of the Order (biology), order Rodentia ( ), which are characterized by a single pair of continuously growing incisors in each of the upper and Mandible, lower jaws. About 40% of all mammal specie ...
s.
In the earlier part of the Cenozoic, the world was dominated by the
gastornithid birds, terrestrial
crocodylian
Crocodilia () is an order of semiaquatic, predatory reptiles that are known as crocodilians. They first appeared during the Late Cretaceous and are the closest living relatives of birds. Crocodilians are a type of crocodylomorph pseudosuchian ...
s like ''
Pristichampsus'', large sharks such as
Otodus, and a handful of primitive large mammal groups like
uintatheres,
mesonychians, and
pantodont
Pantodonta is an extinct suborder (or, according to some, an order) of eutherian mammals. These herbivorous mammals were one of the first groups of large mammals to evolve (around 66 million years ago) after the end of the Cretaceous. The la ...
s. 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,
whale
Whales are a widely distributed and diverse group of fully Aquatic animal, aquatic placental mammal, placental marine mammals. As an informal and Colloquialism, colloquial grouping, they correspond to large members of the infraorder Cetacea ...
s,
primate
Primates is an order (biology), order of mammals, which is further divided into the Strepsirrhini, strepsirrhines, which include lemurs, galagos, and Lorisidae, lorisids; and the Haplorhini, haplorhines, which include Tarsiiformes, tarsiers a ...
s,
entelodonts,
sabre-toothed cats,
mastodon
A mastodon, from Ancient Greek μαστός (''mastós''), meaning "breast", and ὀδούς (''odoús'') "tooth", is a member of the genus ''Mammut'' (German for 'mammoth'), which was endemic to North America and lived from the late Miocene to ...
s and
mammoth
A mammoth is any species of the extinct elephantid genus ''Mammuthus.'' They lived from the late Miocene epoch (from around 6.2 million years ago) into the Holocene until about 4,000 years ago, with mammoth species at various times inhabi ...
s,
three-toed horses, giant
rhinoceros
A rhinoceros ( ; ; ; : rhinoceros or rhinoceroses), commonly abbreviated to rhino, is a member of any of the five extant taxon, extant species (or numerous extinct species) of odd-toed ungulates (perissodactyls) in the family (biology), famil ...
like ''
Paraceratherium'', the rhinoceros-like
brontotheres, various bizarre groups of mammals from South America, such as the vaguely elephant-like
pyrotheres and the dog-like marsupial relatives called
borhyaenids and the
monotreme
Monotremes () are mammals of the order Monotremata. They are the only group of living mammals that lay eggs, rather than bearing live young. The extant monotreme species are the platypus and the four species of echidnas. Monotremes are typified ...
s 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.
Diatoms
A diatom (Neo-Latin ''diatoma'') is any member of a large group comprising several Genus, genera of algae, specifically microalgae, found in the oceans, waterways and soils of the world. Living diatoms make up a significant portion of Earth's B ...
, 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.
See also
*
Cretaceous–Paleogene boundary
The Cretaceous–Paleogene (K–Pg) boundary, formerly known as the Cretaceous–Tertiary (K–T) boundary, is a geological signature, usually a thin band of rock containing much more iridium than other bands. The K–Pg boundary marks the end o ...
(K–T boundary)
*
Geologic time scale
The geologic time scale or geological time scale (GTS) is a representation of time based on the rock record of Earth. It is a system of chronological dating that uses chronostratigraphy (the process of relating strata to time) and geochro ...
*
Late Cenozoic Ice Age
The Late Cenozoic Ice Age,National Academy of Sciences - The National Academies Press - Continental Glaciation through Geologic Times https://www.nap.edu/read/11798/chapter/8#80 or Antarctic Glaciation, began 34 million years ago at the Eocene� ...
References
Further reading
*
External links
Western Australian Museum – The Age of the Mammals
{{Authority control
Geological eras
1840s neologisms