273 million years ago human could walked from Africa to South America at a go. Surprisingly, no major water bodies separated them like today. So, concept of transportation by sea was quite unfamiliar. At that era the continents were linked together, creating a supercontinent called Pangea. The word Pangea was derived from the combination of two Greek words, Pan meaning "all" and Gia meaning "earth". It means something like the "entire earth". In fact, Panthalassa was the lone ocean that existed surrounding that supercontinent. There were two other supercontinents that had existed before the creation of Pangea. The oldest one was Rodinia which was formed over a billion years ago. The second one was Pannotia which existed about 600 million years ago. However, each supercontinent had a unique outline and they were located in a different position on the globe.
Pangea is believed to be formed as result of a collision between two large continents Laurasia and Gondwana. Laurasia was composed of present-day North America, Asia and Europe. Whereas Gondwana included the present-day South America, Africa, Antarctica, Arabian Peninsula, and the Indian subcontinent. Through an extended slow process of fracturing and continental drift it got the shape of present seven continents. Sixteenth-century cartographer Abraham Ortelius first noticed that the coastlines of America, Europe and Africa can be fitted together just like puzzle pieces. Geological resemblances in the bedrock further suggested that these continents were once part of a single form. Geophysicist and meteorologist Alfred Wegener in the early 1900s elaborated this idea as "continental drift."2 It portrays large-scale horizontal slow movements of continents relative to one another and to the ocean basins. From time immemorial still it continues. Similarly, the science of plate tectonic states that tectonic plates are large plates of rock that make up the foundation of the Earth's crust and the shape of the continents. The bed rocks of the continents ride or supported by these plates and they are on relentless motion relative to one another. It has affected the global climate, world's geographical positions and evolution of animals. Issues like volcanoes, earthquakes, and tsunamis affect the continental drift.
Primary landmass of earth started to form around 3 billion years ago. Initially through geological process land started emerging from sea. Over the next 300 million years, additional land formed through volcanic action. After the continents broke apart and started to move there distinct boundaries could be traced inside the Panthalassa Ocean. Those divisions have led to the appearances of present oceans and seas. Later weathering of rocks and decomposition of living beings contributed in development of soil.
Few other reasons of motion are strong ocean currents, thermal convection, ridge thrust and slab jerk. As heat from earth's innermost layer or core transfers to the bottom layer of continents bed rock, the rock warms, softens and upsurges. Again, eruption of volcanoes also push out the hot liquids from core. This drives cooler rock downward. The sequence repeats and consequently forms convection current. This blending motion in the bedrocks appear to be a main factor in plate movement.
About 225 million years ago Indian landmass was connected to Australian and African coast. The vast Tethys Sea separated India from the Asian continent.6 When Pangaea broke apart about 200 million years ago, India with Madagascar started their motion northwards. Himalayas, which stretch 2,900 km along the boundary between India and Tibet was formed by huge thrust that was exerted by India on Asian landmass. The mountain formed around 40 to 50 million years ago. Rock density of both continents had similarities and the pressure of the impinging plates could only be released or calmed by pushing the land rocks upward. Movement of India continues to put huge pressure on the Asian continent still.
Fossil analysis also supports the theory of continental drift. Paleontology is the study or analysis of ancient fossils and there evolution. The earliest marine fossils found in eastern coast of South America and western coast of Africa formed about 150 to 200 million years ago. There similarities proof that Atlantic Ocean did not exist then. Ancient rocks on the Brazilian coast also match those found in West Africa. Again, many rocks from Argentina were matching to those found in South Africa. Mesosaurus was a small aquatic reptile that inhabited in coastal areas during the Permian period or 298.9 million to 251.9 million years ago. Fossil samples of Mesosaurus have only been found in regions of Southern Africa and South America. It verifies these continents were once attached and later broke apart. Few fossils of trees found currently in a polar climate normally grew in temperate regions. Geologists have found no proof of ancient glacial action in the northern hemisphere. North America was warm then. Coal beds found in North America, Great Britain match each other. Even motion of the glacier were marked outward in South Africa and Australia. Numerous geological resemblances found between South America and Western Africa.
The fossils of tropical plants, in the form of coal deposits, were found in Antarctica. This lead to the theory that this region was previously much closer to the equator where the climate is moderate and lush vegetation could flourish.
Glossopteris was a shrub or tree-sized fern that grew in abundance in supercontinent Gondwana millions of years before. The Glossopteris leaves were exceptionally long, large, and narrow. There distinct fossil have been found in present day South America, Africa, India, Australia, Madagascar, and Antarctica which were included in Gondwana Continent.
When liquid magma cools and becomes solid rock, some of the minerals in the rock preserve initial record of the direction and strength of the magnetic field. Few ancient rocks magnetic properties analysis does not proof its alignment with present pole. However if the continents are arranged as they were during Pangaea then the rocks are found align to a common pole.
Geologists noticed similarities in rocks of Paleozoic to Mesozoic era found in South America, Australia, India, Africa, and Antarctica. Glacial markings carved into the bedrock are also identical. Even layer of sediments in rocks found in India, Southern Hemisphere, Falkland Island, Antarctica, Madagascar, and Australia matches.
The East African rift valley stretches over 3,000 km from Zimbabwe in the south towards the Gulf of Aden in the north. It divided the African plate into two unequal Somali and Nubian plates. Along that line a 35 mile long crack was marked in the Ethiopian desert in 2005. Subsequently it may extend up to rift lakes of eastern Africa. The Rift is an example of a divergent plate border, where the Earth's tectonic forces are pulling plates away and creating new continental crust. Within next 5 to 10 million years, the tectonic movement will split the African continent into two and generate a new ocean basin. Besides, volcanic activities along the mid-Atlantic ridge is causing the ocean floor to expand and is coercing North and South America further west. Seismic activity may rise if subsequently the North American plate collides with the Pacific Plate.
Plate tectonics science predicts that the continents are moving across the surface at few centimeters per year rate. This will in turn may cause the plates to displace, collide and combine. Current northwards movement of Australia shows that it will one day sideswipe Asia and collide with Korea, Japan and eastern China. Meanwhile, Africa is moving in counterclockwise direction towards Europe. Scientist predict Africa will crash into Europe and Mediterranean Sea will disappear. The present-day continents will slowly converge within next 250 million years to form another mega-continent. The four concepts for the formation of the next supercontinent are named as Novopangea, Pangea Ultima, Aurica and Amasia. Two predict the Atlantic disappearing one predicts the arctic and the final forecasts the loss of the pacific. It will affect climate as it is directly related to ocean circulation.
Analysing drift history can assist in basin modelling for the petroleum industry. Huge petroleum deposits are found in area hundreds of km off the coasts of Brazil and Angola. Knowledge of pre-drift extensions, types of fossil and geologic connectivity is valuable in this exploration.
Our planet is in a constant process of change from the time of its formation 4 billion years ago. Continents have formed and broke apart many times in the past. Collision of plates pushes the rock between them into great mountain ranges with their wedges below. Moreover, deep roots of these mountains hold crust, subside violent motion, lessen the irregular motion of earth around the axis. Due to plate tectonics, minerals and atmospheric gases that are essential for the development and sustaining life on this planet are recycled. Finally, Alfred L. Wegener said, "Continental drift, faults and compressions, earthquakes, volcanicity, transgression cycles and polar wandering are undoubtedly connected causally on a grand scale. Their common intensification in certain periods of the earth's history shows this to be true. However, what is cause and what effect, only the future will unveil."
Mohammad Mahmudur Rahman Niaz is a civil Engineer and a serving Military Officer. Email: firstname.lastname@example.org
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