User:Abyssal/Portal:Cenozoic
The Cenozoic PortalIntroductionThe Cenozoic (/ˌsiːnəˈzoʊ.ɪk, ˌsɛn-/ SEE-nə-ZOH-ik, SEN-ə-; 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, birds, conifers, 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 also 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. (Full article...) Selected article on the Cenozoic world and its legaciesA virus is a submicroscopic infectious agent that replicates only inside the living cells of an organism. Viruses infect all life forms, from animals and plants to microorganisms, including bacteria and archaea. Viruses are found in almost every ecosystem on Earth and are the most numerous type of biological entity. Since Dmitri Ivanovsky's 1892 article describing a non-bacterial pathogen infecting tobacco plants and the discovery of the tobacco mosaic virus by Martinus Beijerinck in 1898, more than 11,000 of the millions of virus species have been described in detail. The study of viruses is known as virology, a subspeciality of microbiology. When infected, a host cell is often forced to rapidly produce thousands of copies of the original virus. When not inside an infected cell or in the process of infecting a cell, viruses exist in the form of independent viral particles, or virions, consisting of (i) genetic material, i.e., long molecules of DNA or RNA that encode the structure of the proteins by which the virus acts; (ii) a protein coat, the capsid, which surrounds and protects the genetic material; and in some cases (iii) an outside envelope of lipids. The shapes of these virus particles range from simple helical and icosahedral forms to more complex structures. Most virus species have virions too small to be seen with an optical microscope and are one-hundredth the size of most bacteria. The origins of viruses in the evolutionary history of life are still unclear. Some viruses may have evolved from plasmids, which are pieces of DNA that can move between cells. Other viruses may have evolved from bacteria. In evolution, viruses are an important means of horizontal gene transfer, which increases genetic diversity in a way analogous to sexual reproduction. Viruses are considered by some biologists to be a life form, because they carry genetic material, reproduce, and evolve through natural selection, although they lack some key characteristics, such as cell structure, that are generally considered necessary criteria for defining life. Because they possess some but not all such qualities, viruses have been described as "organisms at the edge of life" and as replicators. Viruses spread in many ways. One transmission pathway is through disease-bearing organisms known as vectors: for example, viruses are often transmitted from plant to plant by insects that feed on plant sap, such as aphids; and viruses in animals can be carried by blood-sucking insects. Many viruses spread in the air by coughing and sneezing, including influenza viruses, SARS-CoV-2, chickenpox, smallpox, and measles. Norovirus and rotavirus, common causes of viral gastroenteritis, are transmitted by the faecal–oral route, passed by hand-to-mouth contact or in food or water. The infectious dose of norovirus required to produce infection in humans is fewer than 100 particles. HIV is one of several viruses transmitted through sexual contact and by exposure to infected blood. The variety of host cells that a virus can infect is called its host range: this is narrow for viruses specialized to infect only a few species, or broad for viruses capable of infecting many. Viral infections in animals provoke an immune response that usually eliminates the infecting virus. Immune responses can also be produced by vaccines, which confer an artificially acquired immunity to the specific viral infection. Some viruses, including those that cause HIV/AIDS, HPV infection, and viral hepatitis, evade these immune responses and result in chronic infections. Several classes of antiviral drugs have been developed. (Full article...) Selected article on the Cenozoic in human science, culture and economicsThe history of paleontology traces the history of the effort to understand the history of life on Earth by studying the fossil record left behind by living organisms. Since it is concerned with understanding living organisms of the past, paleontology can be considered to be a field of biology, but its historical development has been closely tied to geology and the effort to understand the history of Earth itself. In ancient times, Xenophanes (570–480 BC), Herodotus (484–425 BC), Eratosthenes (276–194 BC), and Strabo (64 BC–24 AD) wrote about fossils of marine organisms, indicating that land was once under water. The ancient Chinese considered them to be dragon bones and documented them as such. During the Middle Ages, fossils were discussed by Persian naturalist Ibn Sina (known as Avicenna in Europe) in The Book of Healing (1027), which proposed a theory of petrifying fluids that Albert of Saxony would elaborate on in the 14th century. The Chinese naturalist Shen Kuo (1031–1095) would propose a theory of climate change based on evidence from petrified bamboo. In early modern Europe, the systematic study of fossils emerged as an integral part of the changes in natural philosophy that occurred during the Age of Reason. The nature of fossils and their relationship to life in the past became better understood during the 17th and 18th centuries, and at the end of the 18th century, the work of Georges Cuvier had ended a long running debate about the reality of extinction, leading to the emergence of paleontology – in association with comparative anatomy – as a scientific discipline. The expanding knowledge of the fossil record also played an increasing role in the development of geology, and stratigraphy in particular. In 1822, the word "paleontology" was used by the editor of a French scientific journal to refer to the study of ancient living organisms through fossils, and the first half of the 19th century saw geological and paleontological activity become increasingly well organized with the growth of geologic societies and museums and an increasing number of professional geologists and fossil specialists. This contributed to a rapid increase in knowledge about the history of life on Earth, and progress towards definition of the geologic time scale largely based on fossil evidence. As knowledge of life's history continued to improve, it became increasingly obvious that there had been some kind of successive order to the development of life. This would encourage early evolutionary theories on the transmutation of species. After Charles Darwin published On the Origin of Species in 1859, much of the focus of paleontology shifted to understanding evolutionary paths, including human evolution, and evolutionary theory. The last half of the 19th century saw a tremendous expansion in paleontological activity, especially in North America. The trend continued in the 20th century with additional regions of the Earth being opened to systematic fossil collection, as demonstrated by a series of important discoveries in China near the end of the 20th century. Many transitional fossils have been discovered, and there is now considered to be abundant evidence of how all classes of vertebrates are related, much of it in the form of transitional fossils. The last few decades of the 20th century saw a renewed interest in mass extinctions and their role in the evolution of life on Earth. There was also a renewed interest in the Cambrian explosion that saw the development of the body plans of most animal phyla. The discovery of fossils of the Ediacaran biota and developments in paleobiology extended knowledge about the history of life back far before the Cambrian. (Full article...) Selected imagesNeed help?Do you have a question about Abyssal/Portal:Cenozoic that you can't find the answer to? Consider asking it at the Wikipedia reference desk. TopicsGeochronology - Paleogene (Paleocene - Eocene - Oligocene) - Neogene (Miocene - Pliocene) - Quaternary (Pleistocene - Holocene) Cenozoic landmasses - Major Cenozoic events - Paleogene biota appearances - Neogene biota appearances - Quaternary biota appearances - Fossil sites - Stratigraphic units - History - History of paleontology - Timeline of paleontology Researchers - Culture - Treatise on Invertebrate Paleontology - Vertebrate Paleontology Quality ContentFeatured Cenozoic articles - Good Cenozoic articles - History of paleontology - Evolutionary history of life SubcategoriesRelated contentAssociated WikimediaThe following Wikimedia Foundation sister projects provide more on this subject:
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