How Long Was The Mesozoic Era

Mesozoic Era, second of Earth'south three major geologic eras of Phanerozoic time. Its proper name is derived from the Greek term for "middle life." The Mesozoic Era began 252.two one thousand thousand years ago, following the conclusion of the Paleozoic Era, and concluded 66 million years ago, at the dawn of the Cenozoic Era. (Come across the geologic time scale.) The major divisions of the Mesozoic Era are, from oldest to youngest, the Triassic Flow, the Jurassic Period, and the Cretaceous Period. The ancestors of major plant and creature groups that exist today first appeared during the Mesozoic, but this era is best known as the time of the dinosaurs.

Earth'due south climate during the Mesozoic Era was more often than not warm, and there was less difference in temperature between equatorial and polar latitudes than there is today. The Mesozoic was a fourth dimension of geologic and biological transition. During this era the continents began to movement into their present-day configurations. A distinct modernization of life-forms occurred, partly considering of the demise of many earlier types of organisms. Three of the 5 largest mass extinctions in Earth history are associated with the Mesozoic: a mass extinction occurred at the boundary betwixt the Mesozoic and the preceding Paleozoic; another occurred within the Mesozoic at the stop of the Triassic Period; and a third occurred at the boundary between the Mesozoic and subsequent Cenozoic, resulting in the demise of the dinosaurs.

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Mesozoic geology

At the offset of the Mesozoic, all of Earth's continents were joined together into the supercontinent of Pangea (run across the map of the Early Triassic). Past the close of the era, Pangea had fragmented into multiple landmasses. The fragmentation began with continental rifting during the Late Triassic. This separated Pangea into the continents of Laurasia and Gondwana. By the Center Jurassic these landmasses had begun further fragmentation. At that time much of Pangea lay between lx° Northward and 60° Due south, and at the Equator the widening Tethys Ocean cutting between Gondwana and Laurasia. When rifting had sufficiently progressed, oceanic spreading centres formed between the landmasses. During the Center Jurassic, Due north America began pulling autonomously from Eurasia and Gondwana. Past the Late Jurassic, Africa had started to split off from S America, and Australia and Antarctica had separated from India (see the map of the Late Jurassic). Virtually the close of the Cretaceous, Republic of madagascar separated from Africa, and South America drifted northwestward (come across the map of the Belatedly Cretaceous).

As the continents rifted and ruptured, thick sequences of marine sediments accumulated in large linear troughs along their margins. Ocean basin deposits of Jurassic historic period are found today in the circum-Pacific region, along the coasts of eastern North America and the Gulf of Mexico, and on the margins of Eurasia and Gondwana (that is, along the northern and southern boundaries of the Tethys Bounding main).

Major mount building (orogeny) began on the western margins of both North and Due south America and betwixt the separating fragments of Gondwana. For instance, the northwesterly motion of North America resulted in a collision of the western border of the North American continental plate with a circuitous of island arcs during the Belatedly Jurassic. And so-called exotic terranes, geologic fragments that differ markedly in stratigraphy, paleomagnetism, and paleontology from adjoining continental chaff, were accreted to the margin of the North American plate. Every bit thrusting occurred in an due east direction, huge granitic batholiths formed in what is at present the Sierra Nevada range along the California-Nevada border. Other notable episodes of mountain building during the Mesozoic include the Sevier and Laramide orogenies, which took place in western North America during Cretaceous time. These events created the Rocky Mountains.

Mesozoic rocks are widely distributed, appearing in diverse parts of the world. A large percentage of these rocks are sedimentary. At diverse times during the Mesozoic, shallow seas invaded continental interiors and and so drained abroad. During Middle Triassic time, a marine incursion—the Muschelkalk Sea—covered the continental interior of Europe. Seas once again transgressed upon the continents between the Early and Belatedly Jurassic and in the Early Cretaceous, leaving extensive beds of sandstone, ironstone, clays, and limestone (see Solnhofen Limestone). A last major transgression of marine waters flooded large segments of all the continents later on in the Cretaceous. These precipitous rises in body of water level and resultant worldwide flooding are thought to have had ii causes. The kickoff was warm global temperatures, which prevented large volumes of water from being sequestered on land in the form of ice sheets. The second was related to accelerated seafloor spreading; the attendant enlargement of ocean ridges displaced enormous amounts of ocean h2o onto the landmasses. Marine transgression was then extensive that in North America, for instance, a seaway spread all the way from the Arctic to the Gulf of Mexico in the Cretaceous Period. Widespread degradation of chalk, clay, black shales, and marl occurred. In parts of North America, lake and river sediments rich in dinosaur fossils were deposited aslope marine sediments. (See Morrison Germination.)

A substantial corporeality of igneous stone besides formed during the Mesozoic. The orogenies of the Jurassic and Cretaceous periods involved volcanism and plutonic intrusion such as occurred during the emplacement of granites and andesites in the Andes of South America during the Belatedly Jurassic. Two of the largest volcanic events in Earth'due south history occurred during the Mesozoic. The Central Atlantic Magmatic Province, a huge volume of basalt, was created at the end of the Triassic during the initial rifting of Pangea. The area of this igneous province originally covered more than than 7 one thousand thousand square km (about 3 million foursquare miles), and its rocks can exist found today from Brazil to France. Despite such a massive volume of basaltic material extruded, volcanic action was probably short-lived, spanning but a few million years. At the end of the Cretaceous, another igneous province, the flood basalts of the Deccan Traps, formed on what is now the Indian subcontinent. Some scientists have suggested that both of these big igneous events may accept injected significant amounts of carbon dioxide and aerosols into the atmosphere, triggering a change in global climate. The timing of these volcanic events appears to overlap the Triassic-Jurassic and Cretaceous-3rd, or Cretaceous-Paleogene, mass extinctions, and they may have played a part in them.

Mesozoic life

The fauna and flora of the Mesozoic were distinctly different from those of the Paleozoic, the largest mass extinction in World history having occurred at the purlieus of the 2 eras, when some 90 pct of all marine invertebrate species and seventy per centum of terrestrial vertebrate genera disappeared. At the showtime of the Mesozoic, the remaining biota began a prolonged recovery of diversity and full population numbers, and ecosystems began to resemble those of modern days. Vertebrates, less severely affected past the extinction than invertebrates, diversified progressively throughout the Triassic. The Triassic terrestrial environs was dominated past the therapsids, sometimes referred to as "mammal-similar reptiles," and the thecodonts, ancestors of dinosaurs and crocodiles, both of which appeared during the Late Triassic. The kickoff true mammals, which were small, shrewlike omnivores, too appeared in the Late Triassic, as did the lizards, turtles, and flight pterosaurs. In the oceans, mollusks—including ammonites, bivalves, and gastropods—became a dominant group. Fishes, sharks, and marine reptiles such as plesiosaurs, nothosaurs, and ichthyosaurs as well swam the Mesozoic seas.

Another major extinction event struck at the close of the Triassic, one that wiped out equally much as twenty percentage of marine families and many terrestrial vertebrates, including therapsids. The cause of this mass extinction is not yet known but may exist related to climatic and oceanographic changes. In all, 35 percent of the existing animal groups suffered extinction.

In the oceans the ammonites and brachiopods recovered from the Late Triassic crisis, thriving in the warm continental seas. Ammonites chop-chop became very common invertebrates in the marine realm and are now of import index fossils for worldwide correlation of Jurassic rock strata. Many other beast forms, including mollusks (notably the bivalves), sharks, and bony fishes, flourished during the Jurassic. During the Jurassic and Cretaceous, the environmental of marine ecosystems began to change, every bit shown by a rapid increase in multifariousness of marine organisms. It is believed that increasing predation pressures caused many marine organisms to develop better defenses and couch more deeply into the seafloor. In response, predators also evolved more-constructive means to catch their prey. These changes are then pregnant that they are called the "Mesozoic Marine Revolution."

The dominant terrestrial vertebrates were dinosaurs, which exhibited great diversity during the Jurassic and Cretaceous. Birds are believed to accept evolved from dinosaur ancestors during the Late Jurassic. Ancestors of living vertebrates, such equally frogs, toads, and salamanders, appeared on land forth with the two important mod mammal groups, the placentals and the marsupials. Plant life besides exhibited a gradual modify toward more-modernistic forms during the class of the Mesozoic. Whereas seed ferns had predominated in the Triassic, forests of palmlike gymnosperms known as cycads and conifers proliferated nether the tropical and temperate conditions that prevailed during the Jurassic. The first flowering plants, or angiosperms, had appeared by the Cretaceous. They radiated chop-chop and supplanted many of the archaic plant groups to become the ascendant form of vegetation past the stop of the Mesozoic.

dinosaurs to scale — dinosaurs to calibration
A selection of dinosaurs grouped by the geologic interval in which they lived.
Encyclopædia Britannica, Inc.

The Mesozoic closed with an extinction issue that devastated many forms of life. In the oceans all the ammonites, reef-edifice rudist bivalves, and marine reptiles died off, as did 90 percentage of the coccolithophores (single-celled plantlike plankton) and foraminifera (single-celled animal-like plankton). On land the dinosaurs and flying reptiles became extinct. The Late Cretaceous extinctions have been variously attributed to such phenomena every bit global tectonics, draining of the continental seas, due north migration of the continents into different and much cooler climatic zones, intensified volcanic activity, and a catastrophic meteorite or asteroid impact. The Cretaceous extinction may very well accept had multiple causes. Equally the landmasses were uplifted by plate tectonism and migrated poleward, the climate of the Late Cretaceous began to deteriorate. In fact, some of the extinctions were not sudden merely rather spanned millions of years, suggesting that a gradual decline of some organisms had already begun before the end of the Cretaceous. All the same, strong evidence supports the contention that a large-scale bear upon played a significant role in the mass extinctions at the end of the Mesozoic, including the sudden disappearance of many groups (such as ammonite and microfossil species), the presence of geochemical and mineralogical signatures that most likely came from extraterrestrial sources, and the discovery of the Chicxulub crater in the Yucatán Peninsula. It is believed that an asteroid with a diameter of virtually 10 km (6 miles) hit the Earth and caused wildfires, acrid rain, months of darkness (because of the large amount of ash injected into the atmosphere), and cold temperatures (caused by increased reflection of solar energy back into space by airborne particles). An intense warming may accept followed, estrus being trapped by atmospheric aerosols. Whatever the crusade, this major mass extinction marks the stop of the Mesozoic Era. The end of the dinosaurs (except birds) and many other forms of life allowed the evolution of mod biota in the Cenozoic Era.

Carol Marie Tang