Cenozoic

adj.
Of, belonging to, or designating the latest era of geologic time, which includes the Tertiary Period and the Quaternary Period and is characterized by the formation of modern continents, glaciation, and the diversification of mammals, birds, and plants.

n.
The Cenozoic Era.

[Greek kainos, new + -ZOIC.]

Cenozoic (Cainozoic) is the youngest and the shortest of the three Phanerozoic geological eras. It represents the geological time (and rocks deposited during that time) extending from the end of the Mesozoic Era to the present day.

Traditional classifications subdivide the Cenozoic Era into two periods (Tertiary and Quaternary) and seven epochs (from oldest to youngest): Paleocene, Eocene, Oligocene, Miocene, Pliocene, Pleistocene, and Holocene. The older five epochs, which together constitute the Tertiary Period, span the time interval from 65 to 1.8 million years before present. The Tertiary is often separated into two subperiods, the Paleogene (Paleocene through Oligocene epochs, also collectively called the Nummulitic in older European literature) and the Neogene (Miocene and Pliocene epochs). These subperiods were introduced by M. Hornes in 1853. The Quaternary Period, which encompasses only the last 1.8 million years, includes the two youngest epochs (Pleistocene and Holocene). Holocene is also often referred to as the Recent, from the old Lyellian classification. Recent stratigraphic opinions are leaning toward abandoning the use of Tertiary and Quaternary (which are seen as the unnecessary holdovers from obsolete classifications) and in favor of retaining Paleogene and Neogene as the prime subdivisions of Cenozoic. See also Eocene; Holocene; Miocene; Oligocene; Paleocene; Pleistocene; Pliocene.

Many of the tectonic events (mountain-building episodes or orogenies, changes in the rates of sea-floor spreading, or tectonic plate convergences) that began in the Mesozoic continued into the Cenozoic. The Laramide orogeny that uplifted the Rocky Mountains in North America, which began as early as Late Jurassic, continued into the Cretaceous and early Cenozoic time. In its post-Cretaceous phase the orogeny comprised a series of diastrophic movements that deformed the crust until some 50 million years ago, when it ended abruptly. The Alpine orogeny, which created much of the Alps, also began in the Mesozoic, but it was most intense in the Cenozoic when European and African plates converged at an increased pace. See also Cretaceous; Jurassic; Mesozoic; Orogeny.

Another major long-term affect of the tectonic uplift of Tibetan Plateau, which is dated to have been significant by 40 million years ago, may have been the initiation of the general global cooling trend that followed this event. The uplifted plateau may have initiated a stronger deflection of the atmospheric jet stream, strengthening of the summer monsoon, and increased rainfall and weathering in the Himalayas. Increased weathering and dissolution of carbonate rock results in greater carbon dioxide drawdown from the atmosphere. The decreased partial pressure of carbon dioxide levels may have ultimately led to the Earth entering into a renewed glacial phase.

The modern circulation and vertical structure of the oceans and the predominantly glacial mode that the Earth is in at present was initiated in the mid-Cenozoic time. The early Cenozoic was a period of transition between the predominantly thermospheric circulation of the Mesozoic and the thermohaline circulation that developed in the mid-Cenozoic. By the mid-Cenozoic the higher latitudes had begun to cool down, especially in the Southern Hemisphere due to the geographic isolation of Antarctica, leading to steeper latitudinal thermal gradients and accentuation of seasonality. The refrigeration of the polar regions gave rise to the cold high-latitude water that sank to form cold bottom water. The development of the psychrosphere (cold deeper layer of the ocean) and the onset of thermohaline circulation are considered to be the most significant events of Cenozoic ocean history, which ushered the Earth into its modern glacial-interglacial cyclic mode.

The Quaternary climatic history is one of repeated alternations between glacial and interglacial periods. At least five major glacial cycles have been identified in the Quaternary of northwestern Europe. The most recent glacial event occurred between 30,000 and 18,000 years ago when much of North America and northern Europe was covered with extensive ice sheets. The late Pliocene and Pleistocene glacial cyclicity led to repeated falls in global sea level as a result of sequestration of water as ice sheets in higher latitudes during the glacial intervals. For example, the sea level is estimated to have risen some 110 m (360 ft) since the end of the last glacial maximum. As a by-product of these repeated drops in sea level and movement of the shorelines toward the basins, large deltas developed at the mouths of the world's major drainage systems during the Quaternary. These bodies of sand and silt constitute ideal reservoirs for hydrocarbon accumulation. See also Delta; Paleoclimatology.

At the end of the Cretaceous a major extinction event had decimated marine biota and only a few species survived into the Cenozoic. The recovery, however, was relatively rapid. During the Paleocene through middle Eocene interval, the overall global sea-level rise enlarged the ecospace for marine organisms, and an associated climatic optimum led to increased speciation through the Paleocene, culminating in high marine diversities during the early and middle Eocene. Limestone-building coral reefs were also widespread in the tropical-temperate climatic belt of the early Cenozoic, and the tropical Tethyan margins were typified by expansive distribution of the larger foraminifera known as Nummulites (giving the Paleogene its informal name of the Nummulitic period). See also Nummulites.

The late Eocene saw a rapid decline in diversities of marine phyto- and zooplankton due to a global withdrawal of the seas from the continental margins and the ensuing deterioration in climate. Marine diversities reached a new low in the mid-Oligocene, when the sea level was at its lowest, having gone through a major withdrawal of seas from the continental margins. The climates associated with low seas were extreme and much less conducive to biotic diversification. The late Oligocene and Neogene as a whole constitute an interval characterized by increasing partitioning of ecological nichesinto tropical, temperate, and higher-latitude climatic belts, and greater differentiation of marine fauna and flora.

Mammals evolved and spread rapidly to become dominant in the Cenozoic. The evolution of grasses in the early Eocene and the wide distribution of grasslands thereafter may have been catalytic in the diversification of browsing mammals. Marsupials and insectivores as well as rodents (which first appeared in the Eocene) diversified rapidly, as did primates, carnivores, and ungulates. The ancestral horse first appeared in the early Eocene in North America, where its lineage evolved into the modern genus Equus, only to disappear from the continent in the late Pleistocene. A complete evolution of the horse can be followed in North America during the Cenozoic. Increase in overall size, reduction in the number of toes, and increasing complexity of grinding surface of the molars over time are some of the obvious trends. Hominoid evolution began during the Miocene in Africa. Modern hominids are known to have branched off from the hominoids some 5 million years ago. Over the next 4.5 million years the hominids went through several evolutionary stages to finally evolve into archaic Homo sapiens about 1 million years ago. Truly modern Homosapiens do not enter the scene until around 100 thousand years ago. See also Dinosaur; Fossil humans; Mammalia; Organic evolution.

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Cainozoic

The most recent era of earth's history stretching approximately from 65 million years bp to the present day.

Note: click on a word meaning below to see its connections and related words.

The noun has one meaning:

Meaning #1: approximately the last 63 million years
  Synonyms: Cenozoic era, Age of Mammals

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