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The Cenozoic Portal

Introduction

The 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...)

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Selected article on the Cenozoic world and its legacies

Scanning electron micrograph of Escherichia coli rods

Bacteria (/bækˈtɪəriə/ ^ⓘ; sg.: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were among the first life forms to appear on Earth, and are present in most of its habitats. Bacteria inhabit the air, soil, water, acidic hot springs, radioactive waste, and the deep biosphere of Earth's crust. Bacteria play a vital role in many stages of the nutrient cycle by recycling nutrients and the fixation of nitrogen from the atmosphere. The nutrient cycle includes the decomposition of dead bodies; bacteria are responsible for the putrefaction stage in this process. In the biological communities surrounding hydrothermal vents and cold seeps, extremophile bacteria provide the nutrients needed to sustain life by converting dissolved compounds, such as hydrogen sulphide and methane, to energy. Bacteria also live in mutualistic, commensal and parasitic relationships with plants and animals. Most bacteria have not been characterised and there are many species that cannot be grown in the laboratory. The study of bacteria is known as bacteriology, a branch of microbiology.

Like all animals, humans carry vast numbers (approximately 10¹³ to 10¹⁴) of bacteria. Most are in the gut, though there are many on the skin. Most of the bacteria in and on the body are harmless or rendered so by the protective effects of the immune system, and many are beneficial, particularly the ones in the gut. However, several species of bacteria are pathogenic and cause infectious diseases, including cholera, syphilis, anthrax, leprosy, tuberculosis, tetanus and bubonic plague. The most common fatal bacterial diseases are respiratory infections. Antibiotics are used to treat bacterial infections and are also used in farming, making antibiotic resistance a growing problem. Bacteria are important in sewage treatment and the breakdown of oil spills, the production of cheese and yogurt through fermentation, the recovery of gold, palladium, copper and other metals in the mining sector (biomining, bioleaching), as well as in biotechnology, and the manufacture of antibiotics and other chemicals.

Once regarded as plants constituting the class Schizomycetes ("fission fungi"), bacteria are now classified as prokaryotes. Unlike cells of animals and other eukaryotes, bacterial cells do not contain a nucleus and rarely harbour membrane-bound organelles. Although the term bacteria traditionally included all prokaryotes, the scientific classification changed after the discovery in the 1990s that prokaryotes consist of two very different groups of organisms that evolved from an ancient common ancestor. These evolutionary domains are called Bacteria and Archaea. (Full article...)

Selected article on the Cenozoic in human science, culture and economics

Paleontology (/ˌpeɪliɒnˈtɒlədʒi, ˌpæli-, -ən-/ PAY-lee-on-TOL-ə-jee, PAL-ee-, -⁠ən-), also spelled palaeontology or palæontology, is the scientific study of life that existed prior to the start of the Holocene epoch (roughly 11,700 years before present). It includes the study of fossils to classify organisms and study their interactions with each other and their environments (their paleoecology). Paleontological observations have been documented as far back as the 5th century BC. The science became established in the 18th century as a result of Georges Cuvier's work on comparative anatomy, and developed rapidly in the 19th century. The term has been used since 1822 formed from Greek παλαιός ('palaios', "old, ancient"), ὄν ('on', (gen. 'ontos'), "being, creature"), and λόγος ('logos', "speech, thought, study").

Paleontology lies on the border between biology and geology, but it differs from archaeology in that it excludes the study of anatomically modern humans. It now uses techniques drawn from a wide range of sciences, including biochemistry, mathematics, and engineering. Use of all these techniques has enabled paleontologists to discover much of the evolutionary history of life, almost back to when Earth became capable of supporting life, nearly 4 billion years ago. As knowledge has increased, paleontology has developed specialised sub-divisions, some of which focus on different types of fossil organisms while others study ecology and environmental history, such as ancient climates.

Body fossils and trace fossils are the principal types of evidence about ancient life, and geochemical evidence has helped to decipher the evolution of life before there were organisms large enough to leave body fossils. Estimating the dates of these remains is essential but difficult: sometimes adjacent rock layers allow radiometric dating, which provides absolute dates that are accurate to within 0.5%, but more often paleontologists have to rely on relative dating by solving the "jigsaw puzzles" of biostratigraphy (arrangement of rock layers from youngest to oldest). Classifying ancient organisms is also difficult, as many do not fit well into the Linnaean taxonomy classifying living organisms, and paleontologists more often use cladistics to draw up evolutionary "family trees". The final quarter of the 20th century saw the development of molecular phylogenetics, which investigates how closely organisms are related by measuring the similarity of the DNA in their genomes. Molecular phylogenetics has also been used to estimate the dates when species diverged, but there is controversy about the reliability of the molecular clock on which such estimates depend. (Full article...)

Selected images

Image 1Proconsul is an extinct genus of primates that existed from 23 to 25 million years ago during the Miocene epoch
Image 2Fossil tooth of Hyainailurus, an extinct genus of hyaenodont mammal of the family Hyainailouridae that lived during the Miocene
Image 3Adcrocuta is an extinct genus of terrestrial carnivore in the family Hyaenidae that lived during the Miocene period
Image 4Indarctos is a genus of mammals of the bear family, Ursidae, endemic to North America, Europe and Asia during the Miocene
Image 5Mimoperadectes is an extinct genus of didelphimorph marsupial from the Eocene of North America
Image 6Deinotherium was a large prehistoric relative of modern-day elephants that appeared in the Middle Miocene and survived until the Early Pleistocene
Image 7Stegotetrabelodon is an extinct genus of primitive elephant with gomphothere-like anatomical features from the Late Miocene to Early Pliocene of Africa and Eurasia
Image 8Victoriapithecus macinnesi was a primate from middle Miocene central Africa
Image 9Platybelodon ("flat-spear tusk") was a genus of large herbivorous mammals related to the elephant (order Proboscidea). It lived during the late Miocene Epoch in Asia and the Caucasus.
Image 10Palaeotragus ("ancient goat") is a genus of very large, primitive, okapi-like giraffid from the Miocene of Africa, Eurasia.
Image 11Prolibytherium ("Before Libya's Beast") is an extinct climacoceratid artiodactyl ungulate native to Early Miocene North Africa and Pakistan
Image 12Morotopithecus bishopi is a species of fossil ape discovered in Miocene-age deposits of Moroto, Uganda.