Pangaea

Pangaea or Pangea ( /pænˈdʒiːə/) was a supercontinent that existed during the late Paleozoic and early Mesozoic eras. It assembled from earlier continental units approximately 335 million years ago, and it began to break apart about 175 million years ago. In contrast to the present Earth and its distribution of continental mass, much of Pangaea was in the southern hemisphere and surrounded by a superocean, Panthalassa. Pangaea was the most recent supercontinent to have existed and the first to be reconstructed by geologists. The name 'Pangaea/Pangea' is derived from Ancient Greek pan (πᾶν, 'all, entire, whole') and Gaia (Γαῖα, 'Mother Earth, land'). The concept that the continents once formed a contiguous land mass was first proposed by Alfred Wegener, the originator of the scientific theory of continental drift, in his 1912 publication The Origin of Continents (Die Entstehung der Kontinente). He expanded upon his hypothesis in his 1915 book The Origin of Continents and Oceans (Die Entstehung der Kontinente und Ozeane), in which he postulated that, before breaking up and drifting to their present locations, all the continents had formed a single supercontinent that he called the 'Urkontinent'. The name 'Pangea' occurs in the 1920 edition of Die Entstehung der Kontinente und Ozeane, but only once, when Wegener refers to the ancient supercontinent as 'the Pangaea of the Carboniferous'. Wegener used the Germanized form 'Pangäa', but the name entered German and English scientific literature (in 1922 and 1926, respectively) in the Latinized form 'Pangaea' (of the Greek 'Pangaia'), especially due to a symposium of the American Association of Petroleum Geologists in November 1926. The forming of supercontinents and their breaking up appears to have been cyclical through Earth's history. There may have been several others before Pangaea. The fourth-last supercontinent, called Columbia or Nuna, appears to have assembled in the period 2.0–1.8 Ga. Columbia/Nuna broke up and the next supercontinent, Rodinia, formed from the accretion and assembly of its fragments. Rodinia lasted from about 1.1 billion years ago (Ga) until about 750 million years ago, but its exact configuration and geodynamic history are not nearly as well understood as those of the later supercontinents, Pannotia and Pangaea. When Rodinia broke up, it split into three pieces: the supercontinent of Proto-Laurasia, the supercontinent of Proto-Gondwana, and the smaller Congo craton. Proto-Laurasia and Proto-Gondwana were separated by the Proto-Tethys Ocean. Next Proto-Laurasia itself split apart to form the continents of Laurentia, Siberia, and Baltica. Baltica moved to the east of Laurentia, and Siberia moved northeast of Laurentia. The splitting also created two new oceans, the Iapetus Ocean and Paleoasian Ocean. Most of the above masses coalesced again to form the relatively short-lived supercontinent of Pannotia. This supercontinent included large amounts of land near the poles and, near the equator, only a relatively small strip connecting the polar masses. Pannotia lasted until 540 Ma, near the beginning of the Cambrian period and then broke up, giving rise to the continents of Laurentia, Baltica, and the southern supercontinent of Gondwana. In the Cambrian period, the continent of Laurentia, which would later become North America, sat on the equator, with three bordering oceans: the Panthalassic Ocean to the north and west, the Iapetus Ocean to the south, and the Khanty Ocean to the east. In the Earliest Ordovician, around 480 Ma, the microcontinent of Avalonia – a landmass incorporating fragments of what would become eastern Newfoundland, the southern British Isles, and parts of Belgium, northern France, Nova Scotia, New England, South Iberia, and northwest Africa – broke free from Gondwana and began its journey to Laurentia. Baltica, Laurentia, and Avalonia all came together by the end of the Ordovician to form a minor supercontinent called Euramerica or Laurussia, closing the Iapetus Ocean. The collision also resulted in the formation of the northern Appalachians. Siberia sat near Euramerica, with the Khanty Ocean between the two continents. While all this was happening, Gondwana drifted slowly towards the South Pole. This was the first step of the formation of Pangaea. The second step in the formation of Pangaea was the collision of Gondwana with Euramerica. By the Silurian, 440 Ma, Baltica had already collided with Laurentia, forming Euramerica. Avalonia had not yet collided with Laurentia, but as Avalonia inched towards Laurentia, the seaway between them, a remnant of the Iapetus Ocean, was slowly shrinking. Meanwhile, southern Europe broke off from Gondwana and began to move towards Euramerica across the newly formed Rheic Ocean. It collided with southern Baltica in the Devonian, though this microcontinent was an underwater plate. The Iapetus Ocean's sister ocean, the Khanty Ocean, shrank as an island arc from Siberia collided with eastern Baltica (now part of Euramerica). Behind this island arc was a new ocean, the Ural Ocean. By the late Silurian, North and South China split from Gondwana and started to head northward, shrinking the Proto-Tethys Ocean in their path and opening the new Paleo-Tethys Ocean to their south. In the Devonian Period, Gondwana itself headed towards Euramerica, causing the Rheic Ocean to shrink. In the Early Carboniferous, northwest Africa had touched the southeastern coast of Euramerica, creating the southern portion of the Appalachian Mountains, the Meseta Mountains, and the Mauritanide Mountains. South America moved northward to southern Euramerica, while the eastern portion of Gondwana (India, Antarctica, and Australia) headed toward the South Pole from the equator. North and South China were on independent continents. The Kazakhstania microcontinent had collided with Siberia. (Siberia had been a separate continent for millions of years since the deformation of the supercontinent Pannotia in the Middle Carboniferous.)