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Continent - Crusts Compared, Continental Margins, Crustal Origins, Growing Pains, Primeval Continents - Structure of a continent

called sea rock plate

A continent is a large land mass and its surrounding shallow continental shelf. Both are composed of felsic crust. Continents, as by-products of plate tectonic activity, have grown to cover about one-third of Earth's surface over the last four billion years. Continents are unique to Earth, as plate tectonics does not occur on the other planets of our solar system.


Horizontal crustal structure

Continent interiors consist of several structural segments. A rock foundation called the craton composes most of every continent. This consists of several large masses, called terranes, composed of ancient igneous and metamorphic rocks joined together into a rigid, stable unit. Each terrane may be quite different in structure, rock type and age from adjoining terranes. Where exposed at the earth's surface, cratons are called shields. These typically are ancient surfaces planed flat by erosion. In areas where younger sedimentary rocks cover the craton, it is called the stable platform. The craton below these sedimentary layers is usually called basement rock. Ancient mountain chains, or orogenic belts, occur within the craton where two smaller cratons became sutured together in the distant past. Some of the world's highest mountain ranges, such as the Himalayas, developed when two cratons (continents) collided, and erosion has not yet leveled them.

The margins of continents host younger orogenic belts than their interiors. These belts usually form due to plate convergence along active continental margins. Younger orogenic belts, with their steep slopes, tend to shed large volumes of sediment. In coastal regions, these sediments form a seaward-facing, shallowly-sloping land surface called a coastal plain. Within the continental interior, sediments eroded from mountains to form an area of interior lowlands, such as the United States' Great Plains region.

Divergence within a continent's interior leads to rifting. Initially, a steep-sided rift valley forms accompanied by small- to moderate-sized volcanic eruptions. Eventually this rift valley extends to the coast and the valley floor drops below sea level. A small inland sea develops, like the Red Sea between Africa and the Arabian subcontinent, with an oceanic ridge at its center. Given sufficient time and continued sea floor spreading, this sea becomes an ocean, similar to the Atlantic, with passive margins and wide continental shelves along both its shores.

An unusual continental feature develops when a continental rift fails. For whatever reason, rather than divergence producing an inland sea, rifting ends and the structure that remains is called an aulocogen. Depending on the rift's degree of development when failure occurs, the aulocogen may range from an insignificant crustal flaw to a major crustal weakness. Geologists attribute many powerful mid-plate earthquakes, such as the three 1811-1812 New Madrid, Missouri earthquakes, to fault movements associated with failed rifts.

Other common, large-scale continental structures include basins and domes. Basins are circular areas where the crust has subsided, usually under the load of accumulated sediments or due to crustal weakness such as an aulocogen. Domes occur when the crust is uplifted, perhaps due to compression of the continental interior during plate convergence at a nearby active margin.


Vertical crustal structure

Continental crust is heterogenous; however, general trends in structure, composition, and rock type are known. Our knowledge of the subsurface character of the crust comes from two main sources. The crustal interior is observed directly in areas where uplift and erosion expose the cores of ancient mountain belts and other structures. In addition, seismic waves produced during earthquakes change speed and character when moving through the crust. These changes allow geophysicists to infer crustal structure and density.

Continents reach their greatest thickness (up to 45 mi; 70 km) below mountain ranges and are thinnest (10-15 mi; 16-24 km) beneath rifts, aulocogens, shields, and continental margins. Density tends to increase downwards, in part due to an increase in mafic content. The upper crust has an average composition similar to granite, while the lower crust is a mixture of felsic and mafic rocks. Therefore, the average composition of the continents is slightly more mafic than granite. Granite contains an average of 70-75% silica; basalt about 50%. The continental crust is composed of 65% silica, the composition of the igneous rock granodiorite. The intensity of metamorphism and volume of metamorphic rock both increase downward in the crust as well.


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over 9 years ago

A contient is a large land mass and it was a large body of earth but then it was drift and broken into picese of contients called pangea.

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about 1 year ago

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over 5 years ago

this joint was aight so deuces

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over 5 years ago

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over 8 years ago

Earthquake Is Caused By The Rising of Land, Not Drifting of Land. to Seismological research group, respected sir, hearwith i am submiting my research report for publishing in your esteemed magazine. (this article has already been published in leading tamil newspapers and weeklies) yours faithfully,scientist,g.ponmudi.chennai. The Islands of Indonesia are continuously rising.



Soon after Tsunami, which killed more than two and a half lakhs of people and had originated from the island, Sumatra, it was found out that, after the earthquake the north western part of the island simeulue, which was in that region had risen about three feet high above sea level. On account of this, a new shore had formed on the north western part of the island. In addition to that; the sea sponges which were on the sea bed were visible above the sea level!Three months after the earthquake on 26th December, 2004, another quake occurred on 28th March 2005 after which simeulue was found to be four feet above sea level. Apart from this, for an area of about three hundred kilometers, sea sponges which are normally found below the sea could be seen from all visible areas!



Why did the island rise four feet above sea level ?

As the molten rock keeps cooling gradually, the rocky plates that are formed at different levels are of less thickness and density and they keep rising continuously.



The main reason is that, when the molten rock cools, the water and hot gases get released and the rocky plates that are formed are of lesser thickness than the magma in which they formed. Water has a higher density and the ice cubes formed from it have a lower density and they tend to float on water Likewise, the molten rock material which has a higher density produces rocky plates which have a lower density and these move above sea level and form islands.



When new plates are produced by the molten rock material, they start moving upwards thereby pushing the plates which were already formed. The plates suddenly start rising upwards due to intense pressure.



Similar to the ripples that are formed and expanded when a plate of water is hit at the centre from below with a finger, when the island simeulue, which was found in the central part of the Indian Ocean suddenly rose up, the water was pushed aside in all directions and only this resulted in Tsunami.



The frequent occurrences of earthquakes and Tsunami in Indonesia are only due to the sudden rising of the islands.



But, the geologists have come up with a different explanation for the earthquakes which occur there. They say that, about six and a half crores of years ago, India was an island on the southern part of the equator. It moved slowly towards north and collided with Asia about five crores of years ago and it is still continuing its movement. The geologists also opine that due to this movement, when the indo-Australian plate suddenly went below the Burmese plate on December 26th, 2004, an earthquake occurred. There is no truth in what they say because even six and a half crores of years ago India had been part of Asia in the same place as it is found now.



The fossils of mammals which lived in Asia six and a half years ago have been excavated in the form of bones by Professor Ashok Sahani of Punjab University and Professor G.V.R. Prasad of Jammu University in the village of Naskal at Andhra Pradesh and they prove that the above statement is true. So, as per the researchers’ opinion, India had not been an island on the southern part of the equator about six and a half crores of years ago



So, it is proved that even six and a half crores of years ago India had been part of Asia in the same place as it is found now and is not moving in the north eastern direction. Therefore the indo-Australian plate did not go suddenly below the Burmese plate. So the earth quakes on 26 -12 -2004 and 28 – 3 -2005 and the Tsunami are only the result of the rising of the island, simeulue, above its original level. Subject: Rising of the earth’s crust is responsible for producing earthquakes, Submission of report for publishing.



Earthquake is caused due to the movement of the land is a myth.



The most important thing that is missing in this view is that there is no explanation for why earthquake occurs in the centre of the land instead of the peripheral area. Actually the land is rising in different places. This is the reason why earthquakes occur only in the central parts of the land. To be specific, after an earthquake occurred on September 30th of 1993, in the village named Killari, it was found that the land had risen about three feet in height. This shows that the rise of the land is the cause of the earthquake. ‘Reasons for the Rise of the Earth’s Crust’



Earthquake is the effect of the rise of the land



On September 30th 1993, the earthquake that hit the village, killari, situated in central part of India resulted in the death of more than eight thousand people and raised the land surface about three feet high. This elevation was seen in an area of around two kilometers.



Why did the earthquake occur? The quake occurred only in killari, situated in central India and left two kilometers of land area raised. This proves that the earthquake occurred only due to the rise of the land.



Apart from this, the pictures taken by the satellite before the quake showed that the temperature of killari had also risen and the pictures taken after the quake showed it to be normal. After the earthquake occurred, on the borders of Andhra and Karnataka white colored smoke emitted from the ground.



Why did the land rise? Why was the temperature more? Why did the land emit white colored smoke?



We know that the molten rock material called magma is found inside the earth as we have seen it coming out through volcanoes. In the same way, when the molten rock, lava flows on the earth’s surface, we can see the condensed steam and other gases in the form of white colored smoke.



As the water and other hot gases are eliminated as steam, the molten rock cools down and turned in to rock. In the same way when the molten rock inside the earth starts cooling, water and Other hot gases come out in the form of white smoke. Due to this, the temperature of the land rises.



Moreover when the molten rock cools and as the water and hot gases get released, the rocky plates that are formed are of less thickness. For example: water has a higher density and the ice cubes formed from it have a lower density and float on water. Likewise, the molten rock material which has a higher density produces rocky plates which have a lower density and move above the level of the molten rock. In the same way, when new plates are produced by the molten rock material, they start moving upwards there by pushing the plates which were already formed. On account of this movement, the edges of the plates rub against each other thereby causing earthquakes.



For example, in 1356 an earthquake occurred in the city Basel in Switzerland which is situated in central Europe. In the same city, an organization which produces electricity using the heat from underground, drilled two holes of five meters each on the earth in the year 2006.



The project was to send cold water through the first hole which would be changed into steam using the heat of the molten rock and pushed out through the second hole and by rotating dynamos; this would be converted into electricity. But, on the eighth day after the water was sent inside the earth, in the same place, the Richter scale recorded an earthquake with an intensity of 3.4. Even if atom bombs are tested underground, earthquakes do not occur. How could the water which seeped inside produce an earthquake? This clearly shows that the water which seeped inside the earth cooled the molten rock which in turn formed new plates that rose up and caused the earthquake.



Volcanic activity in central Europe

Vogtland, which is situated in central Europe , had often been experiencing a number of minor earthquakes.



In the same place, a researcher by the name Dr,Karin brauer collected the bubbles which came out along with an underground spring in a marshy area and through his research, found out that gases were emitted from a volcano. Based on his research, he says that when the molten rock rises, the pressure of the gases increases and this results in the formation of cracks on rocks which may ultimately result in earthquakes.



But for millions of years in the past, these gases have been coming out of the earth. Apart from this, there are spaces for these gases to be eliminated. We have already seen this fact and the gases do not have enough pressure to bring about an earthquake.



A few years ago from the mountainous part of Nilgiris in India , smoke were seen emanating from earth, but fortunately no earthquake was caused. Likewise, Matsushiro in central Japan also experienced a number of mild quakes. To find out the reason for these quakes, a researcher by the name yoshida collected Water from the hot water springs found there and through experimentation discovered that the water was from the molten rock found underground.



So, she surmises that,” The water which is underground comes out with great pressure and this produces cracks on the rocky plates and this results in earthquakes”. But, the water and gases which are underground have been surfacing through the spaces found between the rocky plates for millions of years in the past. So, the reason for the continuous tremors and the elevation of land is only due to the slow rising of the rocky plates.

For example Wyoming found in central part of North America has more than three hundred hot water springs. Due to the deposit of sulphur from the water, the rocks in that area appear yellowish in colour. So, the area of hot water springs is referred to as yellow Stone Park . Each year that place experiences about two thousand mild tremors. Between January, 2008 and March 2008, 287 tremors have rocked the place.



Moreover it has been found out through satellite research that the land area of 60 miles is continuously raising. To be specific, starting from 2004 till 2006, the land area has been rising at the rate of 2.8 inches every year and has risen to a height of seven inches in three years. It is still rising.But research scholars say that, it is only the effect of the expansion of the molten rock due to heat.



But the surfacing of the water only shows that the molten rock is cooling.



So the release of water and the gases from the molten rock cools the molten rock. This results in the formation of new plates and the rising in the land level in the central part of the continents and results in tremors in those areas only.



There will be an earthquake tomorrow



One week before an earthquake struck the city of haicheng on 30th February, 1975, on the north eastern part of China , it was officially announced that a quake would strike the city.



People abandoned their houses and assembled in an open area in the snow fall. For one week nobody did any work. As announced there was an earthquake of 7.3 magnitudes which was recorded on the Richter scale.

Two thousand and thirteen people lost their lives. It was estimated that if precaution had not been taken, the death toll would have exceeded one and a half lakhs! The whole world looked at China with surprise and when asked, they said that for the past one year slight tremors were occurring and they were gradually getting intensified. They also explained that, during the previous week there was tremendous change in the underground water table.



But, in the next year, the earthquake which struck the city of Tang Shan situated in the north eastern part of China killed two and a half lakhs of people and severely wounded more than one and a half lakhs of people.



The Chinese geologists said that on this occasion there were no preceding tremors. During the earthquake in haicheng, sulphur gas and in Tang Shan carbon-di-oxide were eliminated from underground. Regarding this incident, Carol Raymond is a geophysicist at NASA's, said “Only if we know how an earthquake is caused, we can warn about it in advance”.



How Does an Earthquake occur?

When the rocky plates under the ground rise and their edges rub with each other, an earthquake is caused. Moreover, the water and the gases found between them are under great pressure when these plates rise and so come above the surface of the earth.



Hence, it is understood that the hot gases and water which come out of the earth and the temperature changes are the most authentic warnings of an approaching earthquake. So, by closely and continuously monitoring the temperature changes through satellite observations and finding out the depth and temperature in which the molten rock is found in a particular place, the occurrence of an earthquake can be predicted in advance. Based on it, if precautions are taken, great loss to human life can be prevented. Continents are not drifting, but rising...

In 1835, when scientist Charles Darwin came to Galapagos Island which is located at Pacific Ocean, thousand km far away from South America , he found giant tortoises. He was surprised to see the presence of the tortoise because each one would weigh around 250 kilo, which look like a rock and those tortoises couldn’t float in the sea even for a second.



According to the researchers, these tortoises might come from South America by floating by means of tree branches for two weeks when storm hit. But the tree branches can not float in the same dimension and it will roll and flow. Meantime, these tortoises have no fingers in their legs like elephants. And so, it is not possible for these animals to escape from falling in to the river, when the tree branches roll and flow... It is interrogated such as how this animal could survive for two week with out any food and water. The researchers explained that these animals have the ability to store the enormous fats and water in their body. So they manage to live for two week with out having any food and water.



Moreover, Trevor worth, one of the researchers, has taken the jaw and leg bones of a rat like animal which lived 10 million years ago in the New Zealand , An island which situated two thousand kilometers far away from Australia continent. This animal has a bulged structure on the upper part of the leg bone. So it is found that its locomotion was hopping like kangaroo. Therefore it is impossible for the animal to reach the island by floating tree branches, According to Michael archer, a paleontology researcher.



The researchers said that the tortoises had taken two weeks to reach the Galapagos Island , a thousand kilometer away from South America , by means of floating tree branches. Similarly, it would take at least four weeks far the rat to arrive New Zealand by means of floating tree branches, which is located two thousand kilometer away from Australia .



Could a small animal like rat live for a long period with out having any food and water? Then how the animal reached New Zealand ?



Hear the only possibility is extreme low sea level and exposed land connection, on which the animal migration took place, to reach Remote Island From the Australian continent. Moreover dinosaur’s bones were also found in the island called Chatham which is located near the New Zealand . Indicate the dinosaur’s migration also took place between the continents due to the low sea level of ten thousand feet.



But the presence of closely related dinosaur’s bones on different continents leads to think other researchers differently. They think that all the continents were once jointly present and later separated and drifting apart. But the ancient low sea level of ten thousand feet is the only possible reason for the spreading of ancient animals on other continents.



At the same time the presence of fossils of sea animals such as whales and ammonites indicates that all the continents were once lie under the sea and later rose above sea level. And this rising of land masses caused the earthquake.



Scientist, G. Ponmudi. Chennai I am working as a junior assistant in the health department. And my qualification is Bsc (zoology). I have been working on earthquake research for the past five years. g.ponmudi@yahoo.com



my web site.



www.originofplanets.com