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Antarctica Natural History
.
Antarctica has a total surface of 14,000,000 km2.It is almost completely covered by an ice sheet of 2,000 meters in thickness,though it may exceed 4,000 meters in some areas.
This figure represents about 10 % of all emerged lands and is greater than the surface of Europe and Australia,about half of Africa and almost one third of that of America.
Antarctica is the highest of all continents with a mean of approximately 2,050 meters above sea level.
There are high and extended mountain chains which cross the continent,sometimes exceeding heights of 4,000-4,500 meters a.s.l.
According to scientific evidence,it is believed that approximately 220 million years ago,Gondwanaland (an ancient megacontinent formed by Antarctica,South America,Africa,India,Madagascar and Australia) began to undergo a fragmentation process which,in different geological periods,resulted in the formation of the present continents.
The complete separation of Antarctica from other territories,Australia,the last,occured about 65 million years ago during its drift towards the South Pole.
This also corresponded with the beginning of a new glacial period which created the conditions for the formation of the Antarctic Ice Sheet,dating from approximately 20-25 million years ago.
If all the ice that conceals Antarctica were removed,the continent would be revealed as two different structures,separating by a basin extending from the Weddell to the Ross Seas,over which the ice has built a solid bridge.
The territory on the eastern side is called East Antarctica and is formed by a single continental plate,which represents the nucleus of the original continent.
On the other side,West Antarctica has a much smaller surface area and consist of several island groups of different sizes separated by straits and closed seas.
It originally formed part of the mountain system running along the southern limit of the Pacific Ocean,which was broken up south of Tierra del Fuego during Gondwanaland’s fragmentation to form the so-called Scotia Arch (South Georgia,South Shetland,South Orkney and South Sandwich Islands) and the Antarctic Peninsula.
The Peninsula's geological structure is closely related to the South American Andes Range formation and its mountain system is called the Antarctic Andean Range.
In the past,intense volcanic activity has been a characteristic of the geological evolution of the continent.A dozen volcanos scattered through the region are still active.
The Antarctic Peninsula is the northernmost extremity of Antarctica and the closest to any other continent (1,100 km from South America).
Four different points definable as Poles may be identified in Antarctica.
The Geographical South Pole corresponds to the point at which the earth’s rotation axis passes through the southern hemisphere.It represents the sothernmost latitude (90º),at which all meridians meet.
The Magnetic South Pole is the point at which all the lines of force of the earth’s magnetic field converge.As the magnetic field is not constant,the position of this pole varies accordingly; it is at present located close to the Adelie Land region and its annual displacement is approximately 10-20 km.
The Geomagnetic South Pole indicates the position of the Magnetic Pole taking the earth to be a homogeneous magnet; it is thus a theoretical definition use to analyze the variation in the earth’s magnetic field.It is located at 78º05’S,111ºE.
The Pole of Relative Inaccessibility is the innermost point of the continent and thus the most distant from any coast.It is located at 82º06’S,54º58’E.
The Antarctic Ocean covers a total area of approximately 36,000,000 km2,almost 10 % of the world’s seas.Its southern limit coincides with the antarctic coast,while its northern boundary is defined by an imaginary line running between 50ºS and 60ºS,known as the Antarctic Convergence.
Apart from being an oceanographical limit,the Antarctic Convergence is also a biological frontier; to its south,all forms of life are adapted for survival in a very specialized environment,forming a well defined and separate marine ecosystem.
In the area surrounding the Antarctic Convergence there are a great number of small islands and archipelagos,scattered at the limits of the Pacific,Atlantic and Indian Oceans.
Unlike the antarctic region,this circumpolar zone is usually referred to as the subantarctic area,indicating that particular climate,biological and oceanic features make it a separate ecosystem.
英文快.
优质解答
Antarctica Natural History
.
Antarctica has a total surface of 14,000,000 km2.It is almost completely covered by an ice sheet of 2,000 meters in thickness,though it may exceed 4,000 meters in some areas.
This figure represents about 10 % of all emerged lands and is greater than the surface of Europe and Australia,about half of Africa and almost one third of that of America.
Antarctica is the highest of all continents with a mean of approximately 2,050 meters above sea level.
There are high and extended mountain chains which cross the continent,sometimes exceeding heights of 4,000-4,500 meters a.s.l.
According to scientific evidence,it is believed that approximately 220 million years ago,Gondwanaland (an ancient megacontinent formed by Antarctica,South America,Africa,India,Madagascar and Australia) began to undergo a fragmentation process which,in different geological periods,resulted in the formation of the present continents.
The complete separation of Antarctica from other territories,Australia,the last,occured about 65 million years ago during its drift towards the South Pole.
This also corresponded with the beginning of a new glacial period which created the conditions for the formation of the Antarctic Ice Sheet,dating from approximately 20-25 million years ago.
If all the ice that conceals Antarctica were removed,the continent would be revealed as two different structures,separating by a basin extending from the Weddell to the Ross Seas,over which the ice has built a solid bridge.
The territory on the eastern side is called East Antarctica and is formed by a single continental plate,which represents the nucleus of the original continent.
On the other side,West Antarctica has a much smaller surface area and consist of several island groups of different sizes separated by straits and closed seas.
It originally formed part of the mountain system running along the southern limit of the Pacific Ocean,which was broken up south of Tierra del Fuego during Gondwanaland’s fragmentation to form the so-called Scotia Arch (South Georgia,South Shetland,South Orkney and South Sandwich Islands) and the Antarctic Peninsula.
The Peninsula's geological structure is closely related to the South American Andes Range formation and its mountain system is called the Antarctic Andean Range.
In the past,intense volcanic activity has been a characteristic of the geological evolution of the continent.A dozen volcanos scattered through the region are still active.
The Antarctic Peninsula is the northernmost extremity of Antarctica and the closest to any other continent (1,100 km from South America).
Four different points definable as Poles may be identified in Antarctica.
The Geographical South Pole corresponds to the point at which the earth’s rotation axis passes through the southern hemisphere.It represents the sothernmost latitude (90º),at which all meridians meet.
The Magnetic South Pole is the point at which all the lines of force of the earth’s magnetic field converge.As the magnetic field is not constant,the position of this pole varies accordingly; it is at present located close to the Adelie Land region and its annual displacement is approximately 10-20 km.
The Geomagnetic South Pole indicates the position of the Magnetic Pole taking the earth to be a homogeneous magnet; it is thus a theoretical definition use to analyze the variation in the earth’s magnetic field.It is located at 78º05’S,111ºE.
The Pole of Relative Inaccessibility is the innermost point of the continent and thus the most distant from any coast.It is located at 82º06’S,54º58’E.
The Antarctic Ocean covers a total area of approximately 36,000,000 km2,almost 10 % of the world’s seas.Its southern limit coincides with the antarctic coast,while its northern boundary is defined by an imaginary line running between 50ºS and 60ºS,known as the Antarctic Convergence.
Apart from being an oceanographical limit,the Antarctic Convergence is also a biological frontier; to its south,all forms of life are adapted for survival in a very specialized environment,forming a well defined and separate marine ecosystem.
In the area surrounding the Antarctic Convergence there are a great number of small islands and archipelagos,scattered at the limits of the Pacific,Atlantic and Indian Oceans.
Unlike the antarctic region,this circumpolar zone is usually referred to as the subantarctic area,indicating that particular climate,biological and oceanic features make it a separate ecosystem.
.
Antarctica has a total surface of 14,000,000 km2.It is almost completely covered by an ice sheet of 2,000 meters in thickness,though it may exceed 4,000 meters in some areas.
This figure represents about 10 % of all emerged lands and is greater than the surface of Europe and Australia,about half of Africa and almost one third of that of America.
Antarctica is the highest of all continents with a mean of approximately 2,050 meters above sea level.
There are high and extended mountain chains which cross the continent,sometimes exceeding heights of 4,000-4,500 meters a.s.l.
According to scientific evidence,it is believed that approximately 220 million years ago,Gondwanaland (an ancient megacontinent formed by Antarctica,South America,Africa,India,Madagascar and Australia) began to undergo a fragmentation process which,in different geological periods,resulted in the formation of the present continents.
The complete separation of Antarctica from other territories,Australia,the last,occured about 65 million years ago during its drift towards the South Pole.
This also corresponded with the beginning of a new glacial period which created the conditions for the formation of the Antarctic Ice Sheet,dating from approximately 20-25 million years ago.
If all the ice that conceals Antarctica were removed,the continent would be revealed as two different structures,separating by a basin extending from the Weddell to the Ross Seas,over which the ice has built a solid bridge.
The territory on the eastern side is called East Antarctica and is formed by a single continental plate,which represents the nucleus of the original continent.
On the other side,West Antarctica has a much smaller surface area and consist of several island groups of different sizes separated by straits and closed seas.
It originally formed part of the mountain system running along the southern limit of the Pacific Ocean,which was broken up south of Tierra del Fuego during Gondwanaland’s fragmentation to form the so-called Scotia Arch (South Georgia,South Shetland,South Orkney and South Sandwich Islands) and the Antarctic Peninsula.
The Peninsula's geological structure is closely related to the South American Andes Range formation and its mountain system is called the Antarctic Andean Range.
In the past,intense volcanic activity has been a characteristic of the geological evolution of the continent.A dozen volcanos scattered through the region are still active.
The Antarctic Peninsula is the northernmost extremity of Antarctica and the closest to any other continent (1,100 km from South America).
Four different points definable as Poles may be identified in Antarctica.
The Geographical South Pole corresponds to the point at which the earth’s rotation axis passes through the southern hemisphere.It represents the sothernmost latitude (90º),at which all meridians meet.
The Magnetic South Pole is the point at which all the lines of force of the earth’s magnetic field converge.As the magnetic field is not constant,the position of this pole varies accordingly; it is at present located close to the Adelie Land region and its annual displacement is approximately 10-20 km.
The Geomagnetic South Pole indicates the position of the Magnetic Pole taking the earth to be a homogeneous magnet; it is thus a theoretical definition use to analyze the variation in the earth’s magnetic field.It is located at 78º05’S,111ºE.
The Pole of Relative Inaccessibility is the innermost point of the continent and thus the most distant from any coast.It is located at 82º06’S,54º58’E.
The Antarctic Ocean covers a total area of approximately 36,000,000 km2,almost 10 % of the world’s seas.Its southern limit coincides with the antarctic coast,while its northern boundary is defined by an imaginary line running between 50ºS and 60ºS,known as the Antarctic Convergence.
Apart from being an oceanographical limit,the Antarctic Convergence is also a biological frontier; to its south,all forms of life are adapted for survival in a very specialized environment,forming a well defined and separate marine ecosystem.
In the area surrounding the Antarctic Convergence there are a great number of small islands and archipelagos,scattered at the limits of the Pacific,Atlantic and Indian Oceans.
Unlike the antarctic region,this circumpolar zone is usually referred to as the subantarctic area,indicating that particular climate,biological and oceanic features make it a separate ecosystem.
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