Permian Period (290-248 mya)
A great merger of northern and southern landmasses creates thesupercontinent Pangaea. Stretching from pole to pole and surrounded almost entirelyby a single world ocean called Panthalassa, Pangaea's dry interior fluctuates intemperature far more than its coastal zones, which are moderated by nearby water.
On land, reptiles continue to evolve. Mammal-like reptiles, precursorsto the true mammals, appear and quickly radiate. Seed-producing gymnosperms, which includethe conifers and the cycads, begin to replace lycophytes as the dominantplant group.
In the oceans, brachiopods, ammonoids, crinoids, bony fishes, and sharks still thrive, but rugose corals, tabulate corals,and trilobite populations are on the wane. A catastrophicextinction near the close of the period -- several times worse than any other --nearly ends the entirety of life on land and in the seas.
280 mya: Cycads
With a stout trunk and leafy crown, cycads provide vegetation andcanopy cover to animals. Cycad fossils -- leaves, stems, cones, and seeds -- are foundon every continent, suggesting these gymnosperms thrived in diverse climates over time.Modern species exist only in tropical regions, however.
280 mya: Pangaea supercontinent forms
By the early Permian, Earth's major land masses -- Gondwana,Laurussia, and Siberia -- fuse with smaller continents to form the supercontinentPangaea. Pangaea, which means "all the Earth," stretches nearly from pole to pole.Where plates converge, crust folds and mountains form. Pangaea is surrounded almostentirely by a massive ocean, Panthalassa. A secondary body of water, the Tethys Ocean,cuts into the east of Pangaea near the equator.
280 mya: Drying trend begins
The interior of Pangaea begins to dry.
275 mya: Mammal-like reptiles
Mammal-like reptiles are cold-blooded, but they spawn true,warm-blooded mammalian successors. They are the dominant land vertebrates duringthe Permian, but despite their early success, only two families will survive intothe next period.
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End Permian extinction | ||||
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Date: | | 250 mya | ||
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Intensity: | | 1 | ||
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Affected: | | Approximately 90 percent of allspecies, including nearly 57 percent of marine families and nearly 70 percent ofland vertebrate families go extinct | ||
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Hypotheses: | | Volcanic activity, glaciation,sea-level changes, changes in ocean chemistry, global warming, meteor impact | ||
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Summary: | | In the most devastating ofall extinctions, an estimated 90 percent of all species are eliminated overtwo pulses, spaced about 8 million years apart. All remaining trilobites, all graptolites,and nearly all echinoderms are killed off. The brachiopods,dominant through most of the Paleozoic era, will be only a minor marine invertebrategroup in the Mesozoic and Cenozoic eras. Marine predators such as sharks and coelacanths are hit hard, and coral reefs will require atleast 10 million years to recover. Among the land animals, two-thirds of amphibianfamilies, all large herbivores, and most reptiles die out. Terrestrial plants alsosuffer greatly. The extinction might be the result of a combination offactors, including massive glaciation, changes in sea level, and either anoversupply of carbon dioxide or an undersupply of oxygen in the oceans. Someof these conditions might have been triggered by volcanic eruptions in Siberia,or perhaps even by a meteor impact. | ||
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| Read more The mother of all extinctions (250 mya) Marine communities are at their most diverse, and flora and fauna radiate on land throughout the Permian period. The end Permianextinction is the closest that life has come to complete annihilation in the past600 million years, if not the entire history of Earth.
The extinction generates a complete reorganization of bothmarine and terrestrial life. Dominant groups that vanish leave several ecologicalroles vacant. Many of the groups that fill these roles in the subsequent periodpersist through the Mesozoic and, in some cases, to the present day. The cause of this extinction is still largely unresolved.Some hypotheses suggest that slow but progressive changes in climateor sea level were responsible. Other hypotheses point to quick-hitting, catastrophicevents such as extraordinary volcanic activity. Still others suggest a combinationof factors may have contributed to the mass killing. In 2001, a new hypothesis was put forward. Scientists foundtraces of iridium in rocks dated to the time of the extinction. Iridium is scarcein Earth's crust but plentiful in asteroids, and the scientists think an asteroidas large as seven miles across might have slammed into Earth, releasing at leasta million times more energy than the strongest recorded earthquake. But until moreconclusive evidence like a large impact crater is found, this hypothesis willremain, like others, an intriguing but unproven explanation. | |||||
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