Pangaea
Pangaea or Pangea (derived from Παγγαία, Greek meaning 'all earth') is the name given to the supercontinent that is believed to have existed during the Paleozoic and Mesozoic eras, before the process of plate tectonics separated each of the component continents into their current configuration.
Pangaea broke apart during the Triassic and Jurassic Periods, separating into Laurasia and Gondwana (or Gondwanaland).
The name was apparently first used by the German Alfred Wegener, chief proponent of the continental drift theory, in 1920.
| Phanerozoic eon (542 mya - present) | ||
|---|---|---|
| Paleozoic era | Mesozoic era | Cenozoic era |
| Paleozoic era (542 - 251 mya) | |||||
|---|---|---|---|---|---|
| Cambrian | Ordovician | Silurian | Devonian | Carboniferous | Permian |
| Mesozoic era (251 - 65 mya) | ||
|---|---|---|
| Triassic | Jurassic | Cretaceous |
Geography
In configuration, Pangaea is believed to have been a C-shaped landmass that spread across the equator. The body of water that was believed to have been enclosed within the resulting crescent on the East side has been named the Tethys Sea. Owing to Pangaea's massive size, the inland regions appear to have been very dry, due to the lack of precipitation. The large supercontinent would potentially have allowed terrestrial animals to migrate freely all the way from the South Pole to the North Pole.
The vast ocean that once surrounded the supercontinent of Pangaea has been named Panthalassa. Pangaea is believed to have broken up about 180 million years ago (mya) in the Jurassic period, first into two supercontinents (Gondwana to the south and Laurasia to the north), thereafter into the continents as we understand them today.
Formation of Pangaea
Pangaea was not the first supercontinent believed to have existed. From the evidence available, scientists have reconstructed a predecessor, termed Pannotia, that may have formed about 600 mya, before dividing again some 50 million years later. Another, Rodinia, is believed to have formed approximately 1,100 mya and divided 750 mya. Tentative evidence suggests that the Columbia (supercontinent) existed between 1.8 and 1.5 billion years ago. There is also some evidence for an even earlier supercontinent named Kenorland, existing between ~2.7 billion years to ~2.1 billion years ago, and Earth's probably first supercontinent named Vaalbara, existing between ~3.3 billion years to ~2.8 billion years ago.
Rodinia, which formed 1.1 billion years ago during the Proterozoic, was the supercontinent from which all subsequent continents, sub or super, derived. Rodinia does not preclude the possibility of prior supercontinents as the breakup and formation of supercontinents appear to be cyclical through Earth's 4.6 billion years.
Gondwana followed with several iterations before the formation of Pangaea, which succeeded Pannotia, before the beginning of the Paleozoic Era (545 mya) and the Phanerozoic Eon.
The minor supercontinent of Proto-Laurasia, rifted away from Gondwana, and moved across the Panthalassic Ocean. A new ocean was forming between the two continents, the Proto-Tethys Ocean. Soon, Proto-Laurasia rifted apart itself to create Laurentia, Siberia and Baltica. The rifting also spawned two new oceans, the Iapetus and Khanty Oceans. Baltica remained east of Laurentia, and Siberia sat northeast of Laurentia.
In the Cambrian the independent continent of Laurentia on what would become North America sat on the equator, with three bordering oceans of Panthalassic Ocean to the north and west and Iapetus Ocean to the south, and Khanty Ocean to the east. In the Earliest Ordovician, the microcontinent of Avalonia, a landmass that would become the northeastern United States, Nova Scotia, and England, broke free from Gondwana and began its journey to Laurentia.
Baltica collided with Laurentia by the end of Ordovician, and northern Avalonia collided with Baltica and Laurentia. Laurentia, Baltica, and Avalonia formed to create a minor supercontinent of Euramerica or Laurussia, closing the Iapetus Ocean, while the Rheic Ocean expanded in the southern coast of Avalonia. The collision also resulted in the formation of the Northern Appalachians. Siberia sat near Euramerica, with Khanty Ocean between the two continents. While all this is happening, Gondwana drifted slowly towards the South Pole. This is the first step of the formation of Pangaea.
The second step in the formation of Pangaea is the collision of Gondwana with Euramerica. By Silurian time, Baltica had already collided with Laurentia to form Euramerica. Avalonia hadn't collided with Laurentia yet, and a seaway between them was a remnant of Iapetus Ocean was still shrinking as Avalonia slowly inches towards Laurentia.
Meanwhile, southern Europe fragmented from Gondwana and started to head towards Euramerica across the newly formed Rheic Ocean and collided with southern Baltica in the Devonian. But this microcontinent was an underwater plate. Iapetus Ocean's sister ocean, Khanty Ocean, was also shrinking as an island arc from Siberia collided with eastern Baltica (now part of Euramerica). Behind this island arc was a new ocean, Ural Ocean.
By late Silurian time, North and South China rifted away from Gondwana and started to head northward across the shrinking Proto-Tethys Ocean, and on its southern end, the new ocean, Paleo-Tethys Ocean, opening. In the Devonian Period, Gondwana itself headed towards Euramerica, this caused 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, and the Meseta Mountains. South America moved northward to southern Euramerica, while the eastern portion of Gondwana (India, Antarctica, and Australia) headed towards the South Pole from the equator.
North China and South China were on independent continents. Kazakhstania microcontinent had collided with Siberia (Siberian continent has been a separate continent for millions of years since the deformation of the supercontinent Pannotia) in the Middle Carboniferous.
Western Kazakhstania collided with Baltica in the Late Carboniferous, closing the Ural Ocean between them, and western Proto-Tethys in them (Uralian orogeny), causing the formation of the Ural Mountains, and the formation of the supercontinent of Laurasia. This was the last step of the formation of Pangaea.
Meanwhile, South America had collided with southern Laurentia, closing the Rheic Ocean, and forming the Southernmost part of the Appalachians and Ouachita Mountains. By this time, Gondwana was positioned near the South Pole, and glaciers were forming in Antarctica, India, Australia, and southern Africa and South America. The North China block collided with Siberia by Late Carboniferous time, completely closing Proto-Tethys Ocean.
By Early Permian time, the Cimmerian plate rifted away from Gondwana and headed towards Laurasia, with a new ocean forming in its southern end, the Tethys Ocean, and the closure of the Paleo-Tethys Ocean. Most of the landmasses were all in one. By the Triassic Period, Pangaea rotated a little, towards the southwest direction. The Cimmerian Plate was still travelling across the shrinking Paleo-Tethys, until the Middle Jurassic Time. Paleo-Tethys had closed from west to east, creating the Cimmerian Orogeny. Pangaea looked like a "C", with an ocean inside the "C", the new Tethys Ocean. But Pangaea rifted by the Middle Jurassic, and its deformation is explained below.
Rifting and break-up of Pangaea
There were three major phases in the break-up of Pangaea. The first phase began in the Early-Middle Jurassic, when Pangaea created a rift from the Tethys Ocean from the east and the Pacific from the west. The rifting took place between North America and Africa, the rift produced multiple failed rifts, Mississippi River being the largest. The rift resulted in a new ocean, the Atlantic Ocean.
The Atlantic Ocean did not open uniformly; rifting began in the North-Central Atlantic. The South Atlantic did not open until the Cretaceous. Laurasia started to rotate clockwise and moved northward with North America to the north, and Eurasia to the south. The clockwise motion of Laurasia also lead to the closing of the Tethys Ocean. Meanwhile, in the other side of Africa, new rifts were also forming along the adjacent margins of east Africa, Antarctica, and Madagascar that would lead to the formation of the Southwest Indian Ocean that would also open up in the Cretaceous.
The second, major phase in the break-up of Pangaea began in the Early Cretaceous (150-140 million years ago), when the minor supercontinent of Gondwana separated into four multiple continents (Africa, South America, India and Antarctica/Australia). About 200 million years ago, the continent of Cimmeria, as mentioned above ("The Formation of Pangaea"), collided with Eurasia. However, a subduction zone was forming, as soon as Cimmeria collided.
This subduction zone was called the Tethyan Trench. This trench might have subducted what is called the Tethyan mid-ocean ridge, a ridge responsible for Tethys Ocean's expansion. It probably caused Africa, India and Australia to move northward. In the Early Cretaceous, Atlantica, today's South America and Africa, finally separated from Eastern Gondwana (Antarctica, India, and Australia), causing the opening of a "South Indian Ocean". In the middle Cretaceous, Gondwana fragmented to open up the South Atlantic Ocean as South America started to move westward away from Africa. The South Atlantic did not develop uniformly, rather it rifted from south to north like a zipper.
Also, at the same time Madagascar and India began to separate from Antarctica and moved northward, opening up the Indian Ocean. Madagascar and India separated from each other 100 - 90 million years ago in the Late Cretaceous. India continued to move northward toward Eurasia at 15 centimeters per year (a plate tectonic record), closing the Tethys Ocean, while Madagascar stopped and became locked to the African Plate. New Zealand and New Caledonia began to move from Australia in an eastward direction towards the Pacific, opening the Coral Sea and Tasman Sea. They have been independent islands since.
The third major and final phase of the break-up of Pangaea occurred in the early Cenozoic (Paleocene - Oligocene). North America/Greenland broke free from Eurasia, opening the Norwegian Sea about 60-55 million years ago. The Atlantic and Indian Oceans continued to expand, closing the Tethys Ocean.
Meanwhile, Australia split from Antarctica and moved rapidly northward, just as India did more than 40 million years earlier, and is on a collision course with Eastern Asia. Both Australia and India are currently moving in a northeast direction at 5-6 cm/year. Antarctica has been near or at the South Pole since the formation of Pangaea (since about 280 Ma). India started to collide with Asia beginning about 35 million years ago, forming the Himalayan orogeny, and also finally closing the Tethys Seaway; this collision continues today. The African Plate started to change directions, from west to northwest toward Europe, and South America began to move in a northward direction separating it from Antarctica, allowing complete oceanic circulation around Antarctica for the first time, causing a rapid cooling of the continent and allowing glaciers to form. Other major events took place during the Cenozoic, including the opening of the Gulf of California, the uplift of the Alps, and the opening of the Sea of Japan. The break-up of Pangaea continues today in the East Africa Rift; ongoing collisions may indicate the incipient creation of a new supercontinent.
Appearances in Media
- BBC series of Walking with Monsters, and Walking with Dinosaurs. Some episodes are set in Pangaea
- A National Geographic series of Naked Science: Colliding Continents
- In The Simpsons episode The Seemingly Neverending Story, Mr. Burns says that he was born on Pangaea.
- The Future is Wild, the continents are expected to collide again, creating Pangaea II.
- Someone Still Loves You Boris Yeltsin's album "Broom" features a song called Pangea. It contains the lyrics "Pangea, we used to be together, Why'd we have to drift apart?"
- In the film Ice Age, the force of the acorn was so powerful that it caused the seperation of Pangaea.
External links
- USGS Overview
- Mov video about the moving of Pangea
- In honour of Alfred Wegener, at Alfred Wegener Institute for Polar and Marine Research (AWI) a scientific georeferenced database is called "PANGAEA"
- An explanation of tectonic forces
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