Mesozoic Era

In geologic time , the Mesozoic Era, the second era in the Phanerozoic Eon , spans the time between roughly 250 million years ago (mya) and 65 mya.

The Mesozoic Era contains three geologic time periods including the Triassic Period (250 mya to approximately 206 mya), Jurassic Period (206 mya to approximately 144 mya), and the Cretaceous Period (144 mya to 65 mya).

The Mesozoic Era begins at the end of the Permian Period of the Paleozoic Era . The Mesozoic Era's Cretaceous Period ends with the K-T boundary or K-T event .

During the Mesozoic Era the Pangaean supercontinent spanned Earth's equatorial regions and separated the Panthalassic Ocean and the Tethys Ocean basins. At the start of the Mesozoic Era there was little differentiation or separation between the continental crust that would eventually form the North American, European, South American, and African Continents.

Driven by plate tectonics , by the middle of the Mesozoic Era (approximately 170 mya) the North American and European continents diverged and the earliest form of the Atlantic Ocean emerged between the continents. At mid-Mesozoic Era, although still united along a broad region, what would become the South American and African Plates became distinguishable in a form similar to the modern continents. North America and South America remained united by a dry strip of land similar to the isthmus connection that exists today.

Late in the Mesozoic Era, an increase in sea level allowed the confluence of the now distinguishable Pacific Ocean and Atlantic Ocean to provide a wide water barrier between North and South America. Much of what are now the eastern and middle portions of the United States was flooded. By the end of the Mesozoic Era, water separated South America from Africa . The Australian and Antarctic continents were clearly articulated and the Antarctic continent began a southward migration to the south polar region.

The Mesozoic Era began with a mass extinction and ended with mass extinction. At the end of the Paleozoic Era, almost 80% of marine species became extinct. It would not be until well into the Mesozoic Era that marine life recovered and new reef-building corals evolved. Reptiles dominated the land. Accordingly, the Mesozoic Era is often termed "The Age of Reptiles."

Mesozoic essentially means "middle animals" and marked a fundamental high point in the number and types of species on Earth. Dinosaurs evolved to rule the Mesozoic Era but non-avian species of dinosaurs became extinct as part of the mass extinction that marked the end of the Mesozoic and start of the Cenozoic Era .

The landscape of the Mesozoic Era was also marked by substantial changes in vegetative patterns that altered erosional patterns involved in landscape evolution . During the Mesozoic Era, both gymnosperm (conifers, etc.) and subsequently angiosperm plants evolved in forms comparable to their modern form. Plant growth also allowed the subsequent development of extensive coal beds.

Like the Paleozoic, the Mesozoic Era closed with an episode of extinction. More than 70% of all existing life forms became extinct by the Mesozoic Era–Cenozoic Era boundary (also known as the Cretaceous-Tertiary boundary), including virtually all of the dinosaurs.

During the Mesozoic Era large meteor impacts were frequent. The impact at the start of the Mesozoic Era has been estimated to be of such force as to be able to creating a 350 km impact crater , The K-T event crater (i.e., the Chicxulub crater) measures 170 km in diameter.

See also Archean; Cambrian Period; Cenozoic Era; Dating methods; Devonian Period; Eocene Epoch; Evolution, evidence of; Fossil record; Fossils and fossilization; Geologic time; Historical geology; Holocene Epoch; Miocene Epoch; Mississippian Period; Oligocene Epoch; Ordovician Period; Paleocene Epoch; Pennsylvanian Period; Phanerozoic Eon; Pleistocene Epoch; Pliocene Epoch; Precambrian; Proterozoic Eon; Quaternary Period; Silurian Period; Supercontinents; Tertiary Period

Mesozoic The term ‘Mesozoic’ (Greek: middle life) was first used by Charles Lyell in his pioneering book Principles of geology (1830) to distinguish the rocks formed between the end of the Palaeozoic era and the beginning of the Tertiary (Cenozoic). It was thus roughly equivalent to the old Secondary category of the Italian classifications, and it included the rocks of the Triassic, Jurassic, and Cretaceous periods. Mesozoic rocks occur on all the continents, the Cretaceous being the most widespread and with enormous areas of outcrop in the northern continents and in Australia.

The fossils of the Mesozoic lie between two major extinction events (‘catastrophes’, as some of Lyell's predecessors called them). At the end of the Permian period, about 90 per cent of the marine biota seem to have died off, perhaps suddenly as a result of low global sea level and a profound change in atmospheric composition. This took place about 250 million years ago. A further mass extinction occurred at the end of the Cretaceous period, some 185 Ma later when, many geologists believe, a giant meteorite impact may have been the critical cause.

The biostratigraphical division of the Mesozoic rocks is primarily based upon common marine fossils: ammonoid and belemnite molluscs. The living world of the Mesozoic witnessed the reign of the mammal-like and other reptiles, including dinosaurs, the first appearance of the mammals and birds, the rise of many extant marine invertebrate families and of conifers and flowering plants.

At the beginning of the era the continents were gathered into a single supercontinent, Pangaea, but while moving northwards across the Equator and rotating during Mesozoic times this supercontinent broke up into the major present-day continental masses. Climatic conditions over much of Pangaea were markedly arid to begin with, but in Jurassic and Cretaceous times the climate grew to be predominantly warm and continental to equable. Perhaps associated with the continental movements and with processes in the mantle beneath was the enormous extrusion of basalts in several continents, and prodigious volcanic activity in the ocean basins. Activity in the mantle may also have been responsible for the changeable nature of the Earth's magnetic polarity, which swung from reverse early in the Triassic to normal and back to reverse many times throughout the rest of the era.

D. L. Dineley

Bibliography

Hailwood, E. A. and Kidd, R. B. (eds) (1993) High resolution stratigraphy. Geological Society Special Publication No. 70.
Moulade, M. and and Nairn, A. E. M. (1978) Phanerozoic geology of the world. Mesozoic A. Academic Press, London.
Pomerol, C. (1982) The Cenozoic Era: Tertiary and Quaternary. (Trans. D. and and E. E. Humphries .) Ellis Horwood, Chichester.

Mesozoic era [Gr.,=middle life], major division of geologic time (see Geologic Timescale , table) from 65 to 225 million years ago. Great crustal disturbances that marked the close of the Paleozoic and the beginning of the Mesozoic eras brought about drastic changes in the topography of North America. The Appalachian geosyncline, or downward thrust of the earth's crust, was replaced by the Appalachian Mts., and the eastern part of the continent was elevated during most of the era. The Appalachians were subjected to erosion, the products of which were deposited along the Atlantic coast, which had become a lowland region, or in the ocean beyond. Aside from the Appalachians, the other dry (consistently) areas of the continent were the Canadian Shield, the Antilles areas, and a mountain range elevated in part of the Cordilleran geosyncline. The Mesozoic tectonic activity included numerous subduction zones, such as those along the Pacific margin of the supercontinent Pangaea. Later, Pangaea began to split into the supercontinents of Gondwanaland and Laurasia, and N Africa began to rift apart. By the late Mesozoic, tectonic activity increased dramatically: the new Indian Ocean began to open, the Atlantic Ocean began to open along an extensive rift zone separating the Americas from Europe and Africa (see seafloor spreading ). The life of the Mesozoic was dominated by the reptiles that evolved into the large land-dwelling dinosaurs of the Jurassic and Cretaceous periods. Flying reptiles and birds first appeared during the Mesozoic. Mammals probably evolved from some common ancestor of the reptiles early in the Triassic Period, but were subordinate to the reptiles until the end of the era, when the dominance of reptiles was ended by the extinction of the dinosaurs. Conifers dominated the plant life, with modern pines and sequoias first appearing. Flowering plants, deciduous trees, and grasses also appeared during this era.

Mesozoic The geological era that extended from the end of the Palaeozoic era, about 248 million years ago, to the beginning of the Cenozoic era, about 65 million years ago. It comprises the Triassic, Jurassic, and Cretaceous periods. The Mesozoic era is often known as the Age of Reptiles as these animals, which included the dinosaurs, pterosaurs, and ichthyosaurs, became the dominant lifeform; most became extinct before the end of the era.

Mesozoic The middle of three eras that constitute the Phanerozoic period of time. The Mesozoic (literally ‘middle life’) was preceded by the Palaeozoic Era and followed by the Cenozoic Era. It began with the Triassic approximately 245 Ma ago and ended around 65 Ma at the start of the Tertiary. The Mesozoic comprises the Triassic, Jurassic, and Cretaceous Periods.

Mesozoic The middle of three eras that constitute the Phanerozoic period of time. The Mesozoic (literally ‘middle life’) was preceded by the Palaeozoic Era and followed by the Cenozoic Era. It began with the Triassic approximately 248 Ma ago and ended around 65 Ma at the start of the Tertiary. The Mesozoic comprises the Triassic, Jurassic, and Cretaceous Periods.

Mes·o·zo·ic / ˈmezəˈzōik; ˌmē-/ • adj. Geol. of, relating to, or denoting the era between the Paleozoic and Cenozoic eras, comprising the Triassic, Jurassic, and Cretaceous periods. ∎  [as n.] (the Mesozoic) the Mesozoic era or the system of rocks deposited during it.

Mesozoic Third era of geological time, extending from c.248 to c.65 million years ago. It divides into three periods: the Triassic, Jurassic, and Cretaceous. For most of the era, the continents are believed to have been joined into one huge landmass called Pangaea. The period was also characterized by the variety and size of its reptiles.

Mesozoic The middle of three eras that constitute the Phanerozoic period of time, about 251–65.5 Ma ago. The Mesozoic (literally ‘middle life’) was preceded by the Palaeozoic Era and followed by the Cenozoic Era. The Mesozoic comprises the Triassic, Jurassic, and Cretaceous Periods.

Mesozoic The middle of three eras that constitute the Phanerozoic period of time, about 248–65 Ma ago. The Mesozoic (literally ‘middle life’) was preceded by the Palaeozoic Era and followed by the Cenozoic Era. The Mesozoic comprises the Triassic, Jurassic, and Cretaceous Periods.

Mesozoic •artic, brick, chick, click, crick, dick, flick, hand-pick, hic, hick, kick, lick, mick, miskick, nick, pic, pick, prick, quick, rick, shtick, sic, sick, slick, snick, spic, stick, thick, tic, tick, trick, Vic, wick •alcaic, algebraic, Aramaic, archaic, choleraic, Cyrenaic, deltaic, formulaic, Hebraic, Judaic, Mishnaic, Mithraic, mosaic, Pharisaic, prosaic, Ptolemaic, Romaic, spondaic, stanzaic, trochaic •logorrhoeic (US logorrheic), mythopoeic, onomatopoeic •echoic, heroic, Mesozoic, Palaeozoic (US Paleozoic), Stoic •Bewick •disyllabic, monosyllabic, polysyllabic, syllabic •choriambic, dithyrambic, iambic •alembic •amoebic (US amebic) •aerobic, agoraphobic, claustrophobic, homophobic, hydrophobic, phobic, technophobic, xenophobic •cherubic, cubic, pubic •Arabic, Mozarabic •acerbic • apparatchik • dabchick •peachick