Mesozoic 19322 225205031 2008-07-12T13:18:47Z 147.188.192.41 /* Climate */ {{refimprove|date=December 2007}} The '''Mesozoic Era''' is one of three [[Geologic time scale|geologic eras]] of the [[Phanerozoic]] [[eon (geology)|eon]]. The division of time into eras dates back to [[Giovanni Arduino]], in the 18th century, although his original name for the era now called the 'Mesozoic' was 'Secondary' (making the modern era the '[[Tertiary]]'). Lying between the [[Paleozoic]] and the [[Cenozoic]], Mesozoic means 'middle animals', derived from [[Ancient Greek|Greek]] prefix ''meso-''/''μεσο-'' for 'between' and ''zoon''/''ζωον'' meaning [[animal]] or 'living being'. It is often called the 'Age of the [[Reptile]]s', after the dominant [[fauna]] of the era. The Mesozoic was a time of [[Plate tectonics|tectonic]], [[climate|climatic]] and [[evolution]]ary activity. The continents gradually shifted from a state of connectedness into their present configuration; the drifting provided for [[speciation]] and other important evolutionary developments. The climate was exceptionally warm throughout the period, also playing an important role in the evolution and diversification of new [[animal]] species. By the end of the era, the basis of modern life was in place. ==Geologic periods== Following the Paleozoic, the Mesozoic extended roughly 180 million years: from 251 million years ago ([[Mya (unit)|Mya]]) to when the Cenozoic era began 65 Mya. This time frame is separated into three geologic [[Period (geology)|periods]]. From oldest to youngest: * [[Triassic]] (251.0 Mya to 199.6 Mya) * [[Jurassic]] (199.6 Mya to 145.5 Mya) * [[Cretaceous]] (145.5 Mya to 65.5 Mya) The lower (Triassic) boundary is set by the [[Permian-Triassic extinction event]], during which approximately 90% to 96% of marine species and 70% of terrestrial vertebrates became [[extinction|extinct]]. It is also known as the "Great Dying" because it is considered the largest mass extinction in history. The upper (Cretaceous) boundary is set at the [[Cretaceous–Tertiary extinction event|Cretaceous-Tertiary (KT) extinction event]], which may have been caused by the impactor that created [[Chicxulub Crater]] on the [[Yucatán Peninsula]]. Approximately 50% of all genera became extinct, including all of the non-[[bird|avian]] dinosaurs. ==Tectonics== Compared to the vigorous convergent plate [[orogeny|mountain-building]] of the late Paleozoic, Mesozoic tectonic deformation was comparatively mild. Nevertheless, the era featured the dramatic rifting of the [[supercontinent]] [[Pangaea]]. Pangaea gradually split into a northern continent, [[Laurasia]], and a southern continent, [[Gondwana]]. This created the [[passive continental margin]] that characterizes most of the [[Atlantic]] coastline (such as along the [[East Coast of the United States|U.S. East Coast]]) today. <ref>Stanley, Steven M. ''Earth System History''. New York: W.H. Freeman and Company, 1999. ISBN 0-7167-2882-6</ref> By the end of the era, the continents had rifted into nearly their present form. Laurasia became [[North America]] and [[Eurasia]], while Gondwana split into [[South America]], [[Africa]], [[Australia]], [[Antarctica]] and the [[South Asia|Indian subcontinent]], which collided with the [[Asia]]n plate during the Cenozoic, the impact giving rise to the [[Himalaya]]s. ==Climate== The Triassic was generally dry, a trend that began in the late [[Carboniferous]], and highly seasonal, especially in the interior of Pangaea. Low sea levels may have also exacerbated temperature extremes. With its high [[specific heat capacity]], [[water]] acts as a temperature-stabilizing heat reservoir, and land areas near large bodies of water&mdash;especially the [[ocean]]s&mdash;experience less variation in temperature. Because much of the land that constituted Pangaea was distant from the oceans, temperatures fluctuated greatly, and the interior of Pangaea probably included expansive areas of [[desert]]. Abundant evidence of [[red beds]] and evaporites such as [[salt]] support these conclusions. Sea levels began to rise during the Jurassic, which was probably caused by an increase in [[seafloor spreading]]. The formation of new crust beneath the surface displaced ocean waters by as much as 200 m more than today, which flooded coastal areas. Furthermore, Pangaea began to rift into smaller divisions, bringing more land area in contact with the ocean by forming the [[Tethys Ocean|Tethys Sea]]. Temperatures continued to increase and began to stabilize. [[Humidity]] also increased with the proximity of water, and deserts retreated. The climate of the Cretaceous is less certain and more widely disputed. Higher levels of [[carbon dioxide]] in the [[Earth's atmosphere|atmosphere]] are thought to have caused the [[Temperature gradient|world temperature gradient]] from north to south to become almost flat: temperatures were about the same across the planet. Average temperatures were also higher than today by about 10 °[[Celsius|C]]. In fact, by the middle Cretaceous, equatorial ocean waters (perhaps as warm as 20 °C in the deep ocean) may have been too warm for sea life, and land areas near the equator may have been deserts despite their proximity to water. The circulation of [[oxygen]] to the deep ocean may also have been disrupted. For this reason, large volumes of organic matter accumulated because they were unable to [[Decomposition|decompose]] and were eventually [[deposition|deposited]] as "[[Oil shale|black shale]]". Not all of the data support these hypotheses, however. Even with the overall warmth, temperature fluctuations should have been sufficient for the presence of [[polar ice cap]]s and [[glacier]]s, but there is no evidence of either. Quantitative models have also been unable to recreate the flatness of the Cretaceous temperature gradient.{{Fact|date=December 2007}} ==Life== The extinction of nearly all animal species at the end of the [[Permian]] period allowed for the [[adaptive radiation|radiation]] of many new lifeforms. In particular, the extinction of the large [[herbivore|herbivorous]] and [[carnivore|carnivorous]] [[dinocephalia]] left those [[ecological niche]]s empty. Some were filled by the surviving [[cynodont]]s and [[dicynodont]]s, the latter of which subsequently became extinct. [[Animal]] life during the Mesozoic was dominated, however, by large [[archosaur]]ian [[reptile]]s that appeared a few million years after the Permian extinction: [[dinosaur]]s, [[pterosaur]]s, and aquatic reptiles such as [[ichthyosaur]]s, [[plesiosaur]]s, and [[mosasaur]]s. The climatic changes of the late Jurassic and Cretaceous provided for further adaptive radiation. The Jurassic was the height of archosaur diversity, and the first [[bird]]s and [[Eutheria|placental mammal]]s also appeared. [[Flowering plant|Angiosperms]] radiated sometime in the early Cretaceous, first in the [[tropics]], but the even temperature gradient allowed them to spread toward the poles throughout the period. By the end of the Cretaceous, angiosperms dominated tree floras in many areas, although some evidence suggests that [[biomass]] was still dominated by [[cycad]] and [[fern]]s until after the KT extinction. Some have argued that [[insect]]s diversified with angiosperms because insect [[anatomy]], especially the [[mouth]] parts, seems particularly well-suited for flowering plants. However, all major insect mouth parts preceded angiosperms and insect diversification actually slowed when they arrived, so their anatomy originally must have been suited for some other purpose. As the temperatures in the seas increased, the larger animals of the early Mesozoic gradually began to disappear while smaller animals of all kinds, including [[lizard]]s, [[snake]]s, and perhaps the ancestor [[mammal]]s to [[primate]]s, evolved. The KT extinction exacerbated this trend. The large archosaurs became extinct, while birds and mammals thrived, as they do today. ==References== *''British Mesozoic Fossils'', 1983, The Natural History Museum, London. <references/> ==External links== *[http://www.palaeos.com/Mesozoic/Mesozoic.htm The Mesozoic from Palaeos] *[http://www.emc.maricopa.edu/faculty/farabee/biobk/BioBookPaleo5.html The Mesozoic, age of cycads and dinosaurs] *[http://www.es.ucsc.edu/~pkoch/lectures/lecture19.html Mesozoic terrestrial ecosystems] *[http://www.ace.mmu.ac.uk/Resources/gcc/5-2-2-2.html Mesozoic climates] *[http://www.clas.ufl.edu/users/emartin/GLY3074F01/lecturenotes/Pz-Mzclimate.htm Paleozoic/Mesozoic climate] {{Commonscat|Mesozoic}} {{Phanerozoic Footer}} {{Mesozoic Footer}} [[Category:Geological history of Earth]] [[Category:Mesozoic| ]] [[ar:حقبة وسطى]] [[ast:Mesozoicu]] [[bs:Mezozoik]] [[br:Mezozoeg]] [[bg:Мезозой]] [[ca:Mesozoic]] [[cs:Mezozoikum]] [[da:Mesozoikum]] [[de:Mesozoikum]] [[et:Mesosoikum]] [[es:Era Mesozoica]] [[eo:Mezozoiko]] [[eu:Mesozoikoa]] [[fr:Mésozoïque]] [[ko:중생대]] [[hr:Mezozoik]] [[id:Mesozoikum]] [[is:Miðlífsöld]] [[it:Mesozoico]] [[he:מזוזואיקון]] [[kk:Мезозой]] [[la:Aera Mesozoica]] [[lb:Äerdmëttelalter]] [[lt:Mezozojus]] [[hu:Mezozoikum]] [[ms:Mesozoik]] [[nl:Mesozoïcum]] [[ja:中生代]] [[no:Mesozoikum]] [[nds:Mesozoikum]] [[pl:Era mezozoiczna]] [[pt:Mesozóico]] [[ro:Mezozoic]] [[ru:Мезозой]] [[sk:Mezozoikum]] [[sr:Мезозоик]] [[sh:Mezozoik]] [[fi:Mesotsooinen maailmankausi]] [[sv:Mesozoikum]] [[th:มหายุคมีโซโซอิก]] [[vi:Đại Trung sinh]] [[tr:Mezozoik]] [[uk:Мезозойська ера]] [[zh:中生代]]