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y definition iridium enriched layer associated with a major meteorite impact and subsequent k pg extinction event lower boundary gssp el kef section el kef tunisia 36 09 13 n 8 38 55 e 36 1537 n 8 6486 e 36 1537 8 6486 lower gssp ratified 1991 upper boundary definition n a upper boundary gssp n a upper gssp ratified n a the cenozoic era also known as the caenozoic kainozoic or neozoic era ˌ s iː n ə ˈ z oʊ ɪ k ˌ s ɛ n see nə zoh ik sen ə 2 3 lit new life is earth s current geological era representing the last 66 million years of earth s history it is characterized by the dominance of mammals insects birds and angiosperms 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 commonly known as the age of mammals because the terrestrial animals that dominated both hemispheres were mammals the eutherians placentals in the northern hemisphere and the metatherians marsupials 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 nomenclature edit look up cenozoic or caenozoic in wiktionary the free dictionary cenozoic derives from the ancient greek words kainós καινός new and zōḗ ζωή life 4 the name was proposed in 1840 by the british geologist john phillips 1800 1874 who originally spelled it kainozoic 5 6 7 the era is also known as the cænozoic caenozoic or cainozoic ˌ k aɪ n ə ˈ z oʊ ɪ k ˌ k eɪ 8 9 in name the cenozoic lit new life is comparable to the preceding mesozoic middle life and paleozoic old life eras as well as to the proterozoic earlier life eon divisions edit the cenozoic is divided into three periods the paleogene neogene and quaternary and seven epochs the paleocene eocene oligocene miocene pliocene pleistocene and holocene the quaternary period was officially recognised by the international commission on stratigraphy in june 2009 10 in 2004 the tertiary period was officially replaced by the paleogene and neogene periods the common use of epochs during the cenozoic helps palaeontologists 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 edit 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 epochs the paleocene eocene and oligocene basilosaurus the paleocene epoch lasted from 66 million to 56 million years ago modern placental mammals originated during this time 11 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 12 13 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 14 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 15 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 16 17 the end of the eocene was marked by the eocene oligocene extinction event 18 19 20 the european face of which is known as the grande coupure 21 22 the oligocene 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 23 neogene edit the neogene spans from 23 03 million to 2 58 million years ago it features two epochs the miocene and the pliocene 24 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 leaving only remnants as the black red mediterranean and caspian seas this increased aridity many new plants evolved 95 of modern seed plants families were present by the end of the miocene 25 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 ages reduced sea levels disconnecting the 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 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 26 27 quaternary edit the quaternary 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 megafauna of pleistocene europe mammoths cave lions woolly rhinoceros reindeer horses 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 namib and kalahari deserts many animals evolved including mammoths 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 neanderthals all the continents were affected but africa to a lesser extent it still retains many large animals such as hippos 28 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 29 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 30 31 but the rate may be as high as 500 vertebrate species alone the majority of which have occurred after 1900 32 tectonics edit geologically the cenozoic is the era when the continents moved into their current positions australia new guinea having split from pangea during the early cretaceous drifted north and eventually collided with southeast 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 55 to 45 million years ago creating the himalayas arabia collided with eurasia closing the tethys ocean and creating the zagros mountains around 35 million years ago 33 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 niger nile orange limpopo and zambezi 34 climate edit 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 55 5 million years ago around 50 million years ago 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 co 2 in the air causing a long term reduction in the proportion of this greenhouse gas in the atmosphere around 35 million years ago permanent ice began to build up on antarctica 35 the cooling trend continued in the miocene with relatively short warmer periods when south america became attached to north america creating the isthmus of panama around 2 8 million years ago the arctic region cooled due to the strengthening of the humboldt and gulf stream currents 36 eventually leading to the glaciations of the 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 37 the levels of carbonate ions in the ocean fell over the course of the cenozoic 38 life edit restoration of palaeotherium a paleogene relative of horses that lived in subtropical climates of europe during the eocene 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 39 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 40 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 savannas the age of co dependent flowering plants and insects and the age of birds 41 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 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 gastornithid birds terrestrial crocodylians like pristichampsus large sharks such as otodus and a handful of primitive large mammal groups like uintatheres mesonychians 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 sabre toothed cats mastodons and mammoths three toed horses giant rhinoceros 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 monotremes and marsupials of australia mammal evolution in the cenozoic was predominantly shaped by climatic and geological processes 42 43 cenozoic calcareous nannoplankton experienced rapid rates of speciation and reduced species longevity while suffering prolonged declines in diversity during the eocene and neogene diatoms in contrast experienced major diversification over the eocene especially at high latitudes as the world s oceans cooled 44 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 45 see also edit earth sciences portal cretaceous paleogene boundary k t boundary geologic time scale late cenozoic ice age references edit gallipoli map 2nd ed 1 100 000 carta geologica d italia scala 1 100 000 dipartimento per il servizio geologico d italia 1968 sheet foglio 214 retrieved 31 ...
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