Mesozoic Era (World of Earth Science)
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 Eraenozoic 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