All continents of the earth on a map with names. Geographical location and size of continents. How many parts of the world are there now?
Our planet is more than 4.5 billion years old. And initially there was only one continent on Earth - Kenorland. Due to numerous tectonic movements, this giant continent was repeatedly divided and reassembled, changing its appearance and names. Until the last supercontinent Pangea split into several separate parts. He was the progenitor of modern continents.
A continent (continent) is a huge part of land, surrounded on all sides by the waters of the World Ocean. They are very well isolated from each other and together they occupy a total area of 139 million km2. Currently, there are six continents: Eurasia, Australia, Africa, Antarctica, South America, North America. And although they originated from the same supercontinent, each of them is unique.
Eurasia. It rightfully ranks first on the list. This is the largest continent, its size is more than 53 million km2. The largest country in terms of area, Russia, is located on the territory of Eurasia. The mainland is home to 70% of the world's population, most of whom are from China. The vast expanses of Eurasia combine two parts of the world - Europe and Asia. But this is not the only thing that sets it apart from other continents. This is the only continent washed by four oceans - the Pacific, Atlantic, Indian and Arctic. Eurasia has the deepest lake and the highest mountains, and is rich in a variety of minerals. The continent is famous for its climatic zones and zones, from polar in the north to equatorial in the south. Australia is the smallest continent, its area is about 7.7 million km2. Throughout its entire territory there is only one state with the same name. Most of the surface is occupied by plains. Due to the rare occurrence of mountains and ranges, there are no active volcanoes and earthquakes on the mainland. The fauna is 70% represented by animals that live only in Australia - kangaroos, Tasmanian devils, koalas, platypus.
Planet Earth is very interesting and has not yet been fully explored. Every corner deserves careful treatment and close attention. And then the beauty and uniqueness of our planet will continue to delight its inhabitants.
They differ in geographical location, size and shape, which affects the characteristics of their nature.
Geographical location and size of continents
Continents are distributed unevenly on the Earth's surface. In the Northern Hemisphere they occupy 39% of the surface, and in the Southern Hemisphere they occupy only 19%. For this reason, the Northern Hemisphere of the Earth is called continental, and the Southern Hemisphere is called oceanic.
Based on their position relative to the equator, continents are divided into a group of southern and a group of northern continents.
Since the continents are located at different latitudes, they receive unequal amounts of light and heat from the Sun. In shaping the nature of a continent, its area plays an important role: the larger the continent, the more areas it contains that are remote from the oceans and not affected by them. The relative position of the continents is of great geographical importance.
Geographical location and size of the oceans
The continents that separate them differ from each other in size, water properties, current systems, and features of the organic world.
And they have a similar geographical location: they stretch from the Arctic Circle to. almost entirely in the Southern Hemisphere. It has a special geographical location - it is located around the North Pole within the Arctic Circle, covered with sea ice and isolated from other oceans.
The border between continents and oceans runs along the coastline. It can be straight or rugged, that is, having many protrusions. The rugged coastlines have many seas and bays. Protruding deep into the land, they have a significant impact on the nature of the continents.
Interaction of continents and oceans
Land and water have different properties, but they are constantly in close interaction. The oceans greatly influence the natural processes on the continents, but the continents also take part in shaping the characteristics of the nature of the oceans.
Scientists believe that the Earth has existed for 4.5 billion years. At the same time, life began to emerge on it approximately 4.2 billion years ago. The formation of the Earth's ozone layer and its magnetic field helped protect and preserve developing life on the planet to this day.
Our planet is located third (after Mercury and Venus) from the Sun, which helps it maintain the necessary conditions for life on the planet. The distance from the Earth to the Sun is about 150 million kilometers, or this distance is also called 1 astronomical unit. The air temperature on the planet in the coldest place reaches - 85 degrees Celsius in Antarctica and + 70 degrees Celsius in the hottest part of the planet - the Sahara Desert.
Planet Earth rotates around its own axis and makes one revolution around its axis in 24 Earth hours, which are called days. In one day we have time to see the sunrise, its gradual approach to the horizon, the sunset and the absence of the Sun in the sky, which is again replaced by the sunrise on the horizon. The Earth also revolves around the Sun, and it makes one revolution around the Sun in 365 days or 1 calendar year, as is commonly believed. Over the course of 1 year, the seasons on the planet change, and the changes occur differently in different parts of the planet.
The only natural satellite of the Earth throughout its history has been and remains the Moon. The Moon always faces the Earth with one side, and the other always looks into space. Today, more than 8,000 artificial satellites, sent into space by people, orbit the Earth.
In its shape, planet Earth is similar to an oblate ellipsoid. The planet's diameter is 12,742 km and its circumference is 40,000 km. Given its size, the Earth's surface is covered by 70.8% water and only about 29.2% of the planet's surface is land. The highest point of land on our planet is Mount Everest (8,848 km above sea level). And the deepest point on our planet goes 10.994 km below sea level and is called the Mariana Trench.
Oceans and continents of planet Earth
On planet Earth, at one time there were 6 continents (Eurasia, Africa, North America, South America, Australia and Antarctica) and 6 parts of the world (Australia, Asia, America, Antarctica, Africa and Europe), which differ in their borders from each other . All continents and parts of the world are washed by 5 oceans of the planet: the Pacific Ocean, the Indian Ocean, the Atlantic Ocean and the Arctic Ocean. Since 2000, a fifth ocean of the planet has been added - the Southern Ocean, which is essentially the southern part of all oceans except the Arctic and washes the shores of the continent of Antarctica.
The structure of planet Earth
In the center of the planet there is a core whose size reaches 7000 km in width. The average radius of the core is 3500 km, of which the inner part of the core is solid (1300 km), consists mainly of metal and nickel, and the outer part of the core (2200 km) is in a liquid state. It is the movement of the outer part of the core that forms the Earth's magnetic field, which protects all living things from cosmic radiation.
The core is followed by the mantle (which goes 2800 km deep into the Earth) - it is partially in a liquid state. Scientists have divided the mantle into the Lower and Upper Mantle. The lower mantle reaches a depth of up to 600 km from the surface of the planet. And the Lower Mantle ends at a depth of 2800 km from the Earth's surface.
And above the mantle is the earth's crust, which we know as the top layer of the earth. Its thickness reaches from 10 to 70 km. The earth's crust consists of huge plates that can move and collide with each other, resulting in the formation of mountains and powerful earthquakes.
The atmosphere of planet Earth consists of 77% nitrogen, 22% oxygen and 1% gases. This ratio of substances in the atmosphere turned out to be ideal for all living creatures that live on the planet and plants.
Today, the planet is inhabited by millions of different forms of life (animals, plants, birds, insects, fish, etc.), including people, whose number in 2011 exceeded the threshold of 7 billion people and continues to grow. Our planet is rich in beautiful and amazing places that fascinate with their beauty and mystery. And also has its own records!
Over the years of its existence, humanity has made great progress in terms of technology development, but has caused enormous damage to the planet itself. I would like to believe that soon people will begin to correct their mistakes and save the planet from their harmful effects. Otherwise, no one will survive on this beautiful planet.
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In this article you will learn how many continents are there on earth and all the detailed information about them.
About 71% of the earth's surface is occupied by the World Ocean, and the remaining land surface is distributed between continents.
By definition, a continent is a large massif of the earth's crust rising above the level of the World Ocean. Oddly enough, the number of continents is not generally accepted, ranging from 4 to 7 in different countries. In the post-Soviet space, there are 6 continents with the following area of million km 2:
- Eurasia – 54;
- Africa – 30;
- Antarctica – 14;
- Australia – 9.5;
- North America –24;
- South America -18.
The largest continent, Eurasia, includes two parts of the world - Europe and Asia. The two American continents, on the contrary, make up one part of the world - America. The remaining continents coincide with the parts of the world of the same name.
Mainland - Eurasia
Eurasia accounts for a third of the entire earth's landmass, where ¾ of the total population is concentrated. Here are the largest countries in the world in terms of territory and population. Russia occupies over 17 million km2, and the population of China at the beginning of 2016 was 1 billion 375 million people.
The territory of Asia occupies 80% of the entire Eurasian continent. With an average altitude of 830 m above sea level, this continent is the highest.
Eurasia owns several more geographical records:
- Chomolungma (Everest) is the highest mountain on the planet (8848 m);
- Baikal is the deepest lake on Earth (1642 m), and the Caspian Sea is the largest;
- The Mariana Trench of the Dead Sea is the deepest ocean floor (about 11 km);
- the shallowest is the Sea of Azov, and the largest is the Mediterranean.
Continent - Africa (how many continents are there on earth)
The African continent has the largest number of states - 53. Africa is home to the largest diamond deposits and the highest level of diamond mining, often illegal.
This fact has virtually no effect on the material standard of living, which here, with rare exceptions, is very low.
Africa is home to the largest desert on earth, the Sahara. Africa stands out for its richness of animal life, among which the cheetah is the fastest animal on the planet.
Everyone knows the Egyptian pyramids. But few people know that there are many more pyramids in the largest African country - Sudan. It’s hard to believe, but in Africa, in Morocco, there is a good ski resort called Ifrane, located at an altitude of 1600 m.
Continent - Antarctica (how many continents are there on earth)
The ice of Antarctica makes up 90% of all the earth's ice and contains 70% of all the earth's fresh water reserves. The average ice thickness exceeds 2 m. The largest iceberg discovered was 300 km long and 37 km wide.
Surprisingly, it is Antarctica, and not Africa, that is the driest continent on earth. Only 10 cm of precipitation per year is recorded here - less than in African deserts.
Antarctica belongs to no one. There are no time zones here either. No one lives permanently on the mainland, and the temporary population consists of participants in scientific expeditions.
The climate of Antarctica is too harsh even for polar bears, which are not there, contrary to popular belief. Most of the continent is inhabited by penguins.
Continent - Australia (how many continents are there on earth)
The smallest continent on earth consists of a single state - the Commonwealth of Australia. A third of the continent is desert, making Australia the driest inhabited continent.
At the same time, the Australian Snowy Mountains receive more snow than the Swiss Alps.
Tasmania, one of 6 Australian states, has the cleanest air in the world, and the country as a whole is famous for its ideal ecology.
The longest road in the world in the Nullarbor Desert is 146 km long, and the Great Barrier Coral Reef stretches for 2600 km.
There are a lot of kangaroos, sheep, and especially rabbits in Australia. It was to protect sheep pastures from rabbits and dingoes that the longest fence in the world, 8.5 thousand km, was built.
Continent - North America (how many continents are there on earth)
The border between the United States and Canada, which is almost 9 thousand km, is not guarded. Partially it passes through residential buildings. The island of Greenland, geographically belonging to the North American continent, belongs to the European state of Denmark.
The Bay of Fundy on the east coast of Canada is home to the highest tides in the world's oceans, reaching 18 m. Under the influence of a tidal wave, the waterfall located here reverses its direction of movement.
North America recorded the highest temperatures on Earth. In 1913, it was 57 0 C in Death Valley, California.
Sequoia grows on the North American continent - the most ancient representative of the earth's flora. These trees reach 150 m in height and 20 m in width.
Continent - South America (how many continents are there on earth)
Many people know that Colombia is named after the Spanish navigator. The name Venezuela also has European roots. Amerigo Vespucci (who gave the name to the entire continent), having studied the features of the development of Venezuela, found similarities with Venice.
And the Panama hat was invented not in the country of the same name, but in Ecuador, named after the word “equator”.
This continent holds several geographical records:
- The Amazon, with a length of about 7 thousand km, is the largest river on earth;
- the height of the Venezuelan Angel Falls exceeds a kilometer;
- the highest capital in the world is Bolivian La Paz, whose height reaches 4 km;
- in the Atacama Desert in northern Chile there has been no precipitation for centuries (!).
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THEME CONTINENTS AND OCEANS
Continents and parts of the world
Two qualitatively different types of the earth's crust - continental and oceanic - correspond to two main levels of planetary relief - the surface of the continents and the bed of the oceans.
Structural-tectonic principle of separation of continents. The fundamentally qualitative difference between the continental and oceanic crust, as well as some significant differences in the structure of the upper mantle under the continents and oceans, oblige us to distinguish continents not according to their apparent surroundings by oceans, but according to the structural-tectonic principle. The structural-tectonic principle states that, firstly, the continent includes a continental shelf (shelf) and a continental slope; secondly, at the base of every continent there is a core or ancient platform; thirdly, each continental block is isostatically balanced in the upper mantle.
From the point of view of the structural-tectonic principle, a continent is an isostatically balanced massif of the continental crust, which has a structural core in the form of an ancient platform, to which younger folded structures are adjacent.
There are six continents in total on Earth: Eurasia, Africa, North America, South America, Antarctica and Australia. Each continent contains one platform, and at the base of Eurasia alone there are six of them: Eastern European, Siberian, Chinese, Tarim (Western China, Taklamakan Desert), Arabian and Hindustan. The Arabian and Hindu platforms are parts of ancient Gondwana, adjacent to Eurasia. Thus, Eurasia is a heterogeneous anomalous continent.
The boundaries between the continents are quite obvious. The border between North America and South America runs along the Panama Canal. The border between Eurasia and Africa is drawn along the Suez Canal. The Bering Strait separates Eurasia from North America.
Two rows of continents . In modern geography, the following two series of continents are distinguished: 1. Equatorial series of continents (Africa, Australia and South America).
2. Northern series of continents (Eurasia and North America).
Antarctica, the southernmost and coldest continent, remains outside these ranks.
The modern location of the continents reflects the long history of the development of the continental lithosphere. The southern continents (Africa, South America, Australia and Antarctica) are parts (“fragments”) of the single Paleozoic megacontinent Gondwana. The northern continents at that time were united into another megacontinent - Laurasia. Between Laurasia and Gondwana in the Paleozoic and Mesozoic there was a system of vast marine basins called the Tethys Ocean. The Tethys Ocean stretched from North Africa, through southern Europe, the Caucasus, Western Asia, the Himalayas to Indochina and Indonesia. In the Neogene (about 20 million years ago), an Alpine fold belt arose in the place of this geosyncline.
Corresponding to its large size, the supercontinent Gondwana. According to the law of isostasy, it had a thick (up to 50 km) crust, which sank deeply into the mantle. Beneath them, in the asthenosphere, convection currents were especially intense and the softened substance of the mantle was moving actively. This led first to the formation of a bulge in the middle of the continent, and then to its split into separate blocks, which, under the influence of the same convection currents, began to move horizontally. As proven mathematically (L. Euler), the movement of a contour on the surface of a sphere is always accompanied by its rotation. Consequently, parts of Gondwana not only moved, but also unfolded in geographical space.
The first breakup of Gondwana occurred at the Triassic-Jurassic boundary (about 190-195 million years ago); Afro-America seceded. Then, at the Jurassic-Cretaceous boundary (about 135-140 million years ago), South America separated from Africa. At the border of the Mesozoic and Cenozoic (about 65-70 million years ago), the Hindustan block collided with Asia and Antarctica moved away from Australia. In the present geological era, the lithosphere, according to neomobilists, is divided into six plate blocks that continue to move.
The breakup of Gondwana successfully explains the shape of the continents, their geological similarity, as well as the history of the vegetation and animal world of the southern continents.
The history of the split of Laurasia has not been studied as thoroughly as Gondwana.
The concept of parts of the world . In addition to the geologically determined division of land into continents, there is also a division of the earth's surface into separate parts of the world that has developed in the process of cultural and historical development of mankind. There are six parts of the world in total: Europe, Asia, Africa, America, Australia and Oceania, Antarctica. On one continent of Eurasia there are two parts of the world (Europe and Asia), and two continents of the Western Hemisphere (North America and South America) form one part of the world - America.
The border between Europe and Asia is very arbitrary and is drawn along the watershed line of the Ural ridge, the Ural River, the northern part of the Caspian Sea and the Kuma-Manych depression. Deep fault lines that separate Europe from Asia run through the Urals and the Caucasus.
Area of continents and oceans. Land area is calculated within the modern coastline. The surface area of the globe is approximately 510.2 million km 2. About 361.06 million km 2 is occupied by the World Ocean, which is approximately 70.8% of the total surface of the Earth. The land area accounts for approximately 149.02 million km2, which is about 29.2% of the surface of our planet.
Area of modern continents characterized by the following values: Eurasia - 53.45 km 2, including Asia - 43.45 million km 2, Europe - 10.0 million km 2; Africa - 30, 30 million km 2; North America - 24, 25 million km 2; South America - 18.28 million km 2; Antarctica - 13.97 million km 2; Australia - 7.70 million km 2; Australia with Oceania - 8.89 km 2. Modern oceans have an area : Pacific Ocean - 179.68 million km 2; Atlantic Ocean - 93.36 million km 2; Indian Ocean - 74.92 million km 2; Arctic Ocean - 13.10 million km 2.
Between the northern and southern continents, in accordance with their different origins and development, there is a significant difference in area and character of the surface. The main geographical differences between the northern and southern continents are as follows:
1. Eurasia is incomparable in size with other continents, concentrating more than 30% of the planet’s landmass. 2.The northern continents have a significant shelf area. The shelf is especially significant in the Arctic Ocean and the Atlantic Ocean, as well as in the Yellow, Chinese and Bering Seas of the Pacific Ocean. The southern continents, with the exception of the underwater continuation of Australia in the Arafura Sea, are almost devoid of a shelf. 3. Most of the southern continents lie on ancient platforms. In North America and Eurasia, ancient platforms occupy a smaller part of the total area, and most of them occur in areas formed by Paleozoic and Mesozoic orogeny. In Africa, 96% of its territory is in platform areas and only 4% is in mountains of Paleozoic and Mesozoic age. In Asia, only 27% is on ancient platforms and 77% on mountains of various ages. 4. The coastline of the southern continents, formed mostly by rifts, is relatively straight; There are few peninsulas and mainland islands. The northern continents are characterized by an exceptionally winding coastline, an abundance of islands, peninsulas, often extending far into the ocean. Of the total area, islands and peninsulas account for about 39% in Europe, North America - 25%, Asia - 24%, Africa - 2.1%, South America - 1.1% and Australia (excluding Oceania) - 1.1% .
Vertical dissection of land
Each of the main planetary levels - the surface of the continents and the ocean floor - breaks down into a number of minor levels. The formation of both major and minor levels occurred during the long-term development of the earth's crust and continues to this day. Let us dwell on the modern division of the continental crust into high-altitude levels. The steps are counted from sea level.
1.Depression - areas of land that lie below sea level. The largest depression on Earth is the southern part of the Caspian lowland with a minimum elevation of 28 m. Inside Central Asia there is a dry Turfan depression with a depth of about 154 m. The deepest depression on Earth is the Dead Sea basin; The shores of the Dead Sea lie 392 m below sea level. Depressions occupied by water, the levels of which lie above ocean level, are called cryptodepression. Typical examples of cryptodepression are Lake Baikal and Lake Ladoga. The Caspian Sea and Dead Sea are not cryptodepressions because their water levels do not reach ocean levels. The area occupied by depressions (without cryptodepressions) is relatively small and amounts to about 800 thousand km 2.
2. Lowlands (low plains ) – areas of land lying at an altitude of 0 to 200 m above sea level. Lowlands are numerous on every continent (with the exception of Africa) and occupy a significantly larger area than any other level of land. The total area of all the lowland plains of the globe is about 48.2 million km 2.
3. Hills and plateaus lie at an altitude of 2001 to 500 m and differ from each other in the prevailing forms of relief: on the hills the relief is rugged, on the plateau it is relatively flat; the hills rise over the lowlands gradually, and the plateaus rise with a noticeable ledge. They also differ from each other and from their geological structure. The area occupied by hills and plateaus is about 33 million km 2.
Above 500 m there are mountains. They can be of different origins and ages. By height, mountains are divided into low, medium and high.
4.Low mountains they rise no higher than 1,000 m. Typically, low mountains are either ancient destroyed mountains or the foothills of modern mountain systems. Low mountains occupy about 27 million km 2.
5.Middle Mountains have a height of 1,000 to 2,000 m. Examples of medium-altitude mountains are: the Urals, the Carpathians, Transbaikalia, some ranges of Eastern Siberia and many other mountainous countries. The area occupied by medium-sized mountains is about 24 million km 2.
6.High (alpine) mountains rise above 2,000 m. The term “alpine mountains” is often applied only to mountains of Cenozoic age lying at an altitude of more than 3,000 m. The high mountains account for about 16 million km 2.
Below ocean level, the continental lowland continues, flooded with water - the shelf, or continental shoal. Until recently, according to the same conventional account as the stages of land, the shelf was called underwater plains with depths of up to 200 m. Now the shelf boundary is drawn not along a formally chosen isobath, but along the line of the actual, geologically determined end of the continental surface and its transition to the continental slope . Therefore, the shelf continues into the ocean to different depths in each sea, often exceeding 200 m and reaching 700 and even 1,500 m.
At the outer edge of the relatively flat shelf there is a sharp break in the surface towards the continental slope and continental foot. The shelf, slope and foot together form the underwater margin of the continents. It continues to an average depth of 2,450 m.
Continents, including their underwater margins, occupy about 40% of the Earth's surface, while the land area is about 29.2% of the total earth's surface.
Each continent is isostatically balanced in the asthenosphere. There is a direct relationship between the area of the continents, the heights of their relief and the depth of immersion in the mantle. The larger the area of the continent, the greater its average height and thickness of the lithosphere. The average height of the land is 870 m. The average height of Asia is 950 m, Europe – 300 m, Australia – 350 m.
The concept of a hypsometric (bathygraphic) curve. A generalized profile of the earth's surface is presented hypsometric curve . The part of it related to the ocean is called bathygraphic curve . The curve is constructed as follows. The dimensions of areas lying at various heights and depths are taken from hypsometric and bathygraphic maps and plotted in a system of coordinate axes: heights are plotted along the ordinate line from 0 up, and depths downwards, and areas in millions of square kilometers are plotted along the abscissa line.
Relief and structure of the ocean floor
The average depth of the World Ocean is 3,794 m.
The bottom of the World Ocean consists of the following four planetary morphosculptural relief forms:
underwater continental margins,
transition zones,
ocean bed,
mid-ocean ridges.
The underwater margin of continents consists of a shelf, a continental slope, and a continental foot. It descends to a depth of 2,450 m. The earth's crust here is of a continental type. The total area of the underwater continental margins is about 81.5 million km 2. The continental slope plunges into the ocean relatively steeply; the slopes average about 4 0, but sometimes reach 40 0. Structurally, the continental foot is a trough at the boundary of the continental and oceanic crust. Morphologically, it is an accumulative plain formed by sediments carried down from the continental slope.
Mid-ocean ridges are a single and continuous system spanning all oceans. Special geophysical studies reveal increased tectonic activity of mid-ocean ridges. They are huge mountain structures, reaching a width of 1-2 thousand km and rising above the ocean floor by 3-4 thousand km. Sometimes mid-ocean ridges rise above ocean level and form numerous islands (Iceland, Azores, Seychelles, etc.). In terms of grandeur, they significantly surpass the mountainous countries of the continents and are comparable to the continents. For example, the Mid-Atlantic Ridge is several times larger than the largest land-based mountain system, the Cordillera and Andes. However, the name “ridge” is only conditionally applicable to mid-ocean formations.
The system of mid-ocean ridges includes the following structures: - Mid-Atlantic Ridge (stretches from Iceland along the entire ocean to the island of Tristan da Cunha);
Mid-Indian Ridge, the peaks of which are expressed by the Seychelles Islands); - East Pacific Rise running south of the California Peninsula.
According to the relief and characteristics of tectonic activity, mid-ocean ridges are: 1) rift and 2) non-rift.
Rift ridges (for example, the Mid-Atlantic) are characterized by the presence of a “rift” valley - a deep and narrow gorge with steep slopes that runs along the crest of the ridge along its axis. The width of the rift valley is 20-30 km, and the depth of the fault can be located below the ocean floor up to 7,400 m (Romanche Trench). The relief of rift ridges is complex and rugged: rift valleys, narrow mountain ranges, giant transverse faults, intermontane depressions, volcanic cones, underwater volcanoes, islands. All rift ridges are characterized by high seismic activity.
Non-rift ridges (for example, the East Pacific Rise) are characterized by the absence of a “rift” valley and have a less complex topography. Seismic activity is not typical for non-rift ridges. However, they share a common feature of all mid-ocean ridges - the presence of enormous transverse faults.
The most important geophysical features of mid-ocean ridges are as follows:
Increased heat flow from the Earth's interior,
The specific structure of the earth's crust,
Magnetic field anomalies,
Volcanism. -seismic activity.
The distribution of sediments that make up the upper layer of the earth's crust in mid-ocean ridges obeys the following pattern: on the ridge itself, sediments are thin or absent altogether; As one moves away from the ridge, the thickness of the sediments increases (up to several kilometers) and their age. If the lava in the cleft itself is 13 thousand years old, then 60 km away it is already 8 million years old. Rocks older than 160 million years have not been found on the ocean floor. These facts indicate the constant renewal of the ridges.
Mechanisms of formation of mid-ocean ridges . The formation of mid-ocean ridges is associated with upper magma. The upper magma is a huge convection system. The rise of molten material causes the formation of mid-ocean ridges. Along rift valleys, lava flows out and forms a basalt layer. By joining the old crust, new portions of lava cause horizontal displacement of lithospheric blocks and expansion of the ocean floor. The speed of horizontal movements in different places of the Earth ranges from 1 to 12 cm per year: in the Atlantic Ocean - about 4 cm/year; in the Indian Ocean - about 6 cm/year, in the Pacific Ocean - up to 12 cm/year. These insignificant values, multiplied by millions of years, give enormous distances: in the 150 million years that have passed since the split of South America and Africa, they have diverged by 5 thousand km. North America separated from Europe 80 million years ago. And 40 million years ago, Hindustan collided with Asia and the formation of the Himalayas began. As a result of the expansion of the ocean floor in the zone of mid-ocean ridges, there is no increase in earthly matter at all, but only its flow and transformation. The basaltic crust, growing along the mid-ocean ridges and spreading horizontally from them, travels thousands of kilometers over the course of millions of years and, at some edges of the continents, descends again into the bowels of the Earth, taking with it ocean sediments. At the same time, it causes continental drift. This explains the different ages of rocks on the crests of ridges and in other parts of the oceans.
Transition zones include deep-sea trenches, island arcs and basins of marginal seas. In transition zones, areas of continental and oceanic crust are complexly combined.
Deep ocean trenches are found in the following four regions of the Earth: - in the Pacific Ocean along the coasts of East Asia and Oceania: Aleutian Trench, Kuril-Kamchatka Trench, Japan Trench, Philippine Trench, Mariana Trench (with a maximum depth of 11,022 m for the Earth), West Melanesian Trench , Tonga;
In the Indian Ocean - Java Trench;
In the Atlantic Ocean - the Puerto Rican Trench;
In the Southern Ocean - South Sandwich.
The ocean floor, which accounts for about 73% of its total area, is occupied by deep-sea (from 2,450 to 6,000 m) plains. In general, these deep-sea plains correspond to oceanic platforms. Between the plains there are mid-ocean ridges, as well as hills and uplifts of other origins. These rises divide the ocean floor into separate basins. For example, from the North Atlantic Ridge to the west is the North American Basin, and to the east are the Western European and Canary Basins. There are numerous volcanic cones at the bottom of the World Ocean.
Patterns of continental arrangement
1. Most of the land is located in the Northern Hemisphere. The Northern Hemisphere is continental, although here only 39% is land and about 61% is ocean. 2. The northern continents are located quite compactly. The southern continents are located very scattered and disconnected.
3. The planet's topography is anti-semitic. The continents are located in such a way that each of them on the opposite side of the Earth certainly corresponds to an Ocean. This is most obvious in the comparison of the Arctic ocean and Antarctic land. But if the globe is installed so that any of the continents is at one of the poles, then there will definitely be an ocean at the other pole. There is only one minor exception: the end of South America antipodal to Southeast Asia. Antipodality, since it has almost no exceptions, cannot be a random phenomenon. It is based on the balance of all parts of the surface of the rotating Earth.
THEME: ISLANDS
In the process of development of the earth's crust and its interaction with the World Ocean, large and small islands were formed. The total number of islands is constantly changing. Some islands appear, others disappear. For example, delta islands are formed and eroded, ice massifs taken for islands (“lands”) melt, sea spits acquire an island character and, conversely, islands join the land and turn into peninsulas. Therefore, the area of the islands is calculated only approximately. It is about 9.9 million km 2. About 79% of the entire island landmass is located on 28 large islands. Of these, the largest is Greenland (2.2 million km 2).
The 28 largest islands on the globe include the following: 1. Greenland 2. New Guinea
3.Kalimantan (Borneo)
4.Madagascar 5.Baffin Island
6.Sumatra 7.Great Britain 8.Honshu 9.Victoria (Canadian Arctic Archipelago)
10.Ellesmere Land (Canadian Arctic Archipelago)
11.Sulawesi (Celebes)
12.South Island of New Zealand
13.Java 14.North Island of New Zealand
15.Newfoundland 16.Cuba 17.Luzon 18.Iceland 19.Mindanao 20.Novaya Zemlya
21.Haiti 22.Sakhalin 23.Ireland 24.Tasmania 25.Banks (Canadian Arctic Archipelago)
26.Sri Lanka 27.Hokkaido 28.Devon
Both large and small islands are located either singly or in groups. Groups of islands are called archipelagos. Archipelagos can be compact (for example, Franz Josef Land, Spitsbergen, Greater Sunda Islands) or elongated (for example, Japanese, Philippine, Greater and Lesser Antilles). Elongated archipelagos are sometimes called ridges (for example, the Kuril ridge, the Aleutian ridge). Archipelagos of small islands scattered across the expanses of the Pacific Ocean are united into the following three large groups: Melanesia, Micronesia (Caroline Islands, Mariana Islands, Marshall Islands), Polynesia.
By origin, all islands can be grouped as follows:
I. Mainland Islands:
1) platform islands,
2) islands of the continental slope,
3) orogenic islands,
4) island arcs,
5) coastal islands: a) skerries, b) Dalmatian, c) fjord, d) spits and arrows, e) delta.
II. Independent islands:
volcanic islands, including a) fissure lava outpouring, b) central lava outpouring - shield and conical;
coral islands: a) coastal reefs, b) barrier reefs, c) atolls.
Mainland Islands are genetically connected with the continents, but these connections are of a different nature, which affects the nature and age of the islands, their flora and fauna.
Platform Islands lie on a continental shelf and geologically represent a continuation of the mainland. Platform islands are separated from the main landmass by shallow straits or straits. Examples of platform islands are the following: British Isles, Spitsbergen Archipelago, Franz Josef Land, Severnaya Zemlya, New Siberian Islands, Canadian Arctic Archipelago.
The formation of straits and the transformation of part of the continents into islands date back to recent geological time; therefore, the nature of the island land differs little from the mainland.
Islands of the continental slope are also parts of continents, but their separation occurred earlier. These islands are separated from the adjacent continents not by a gentle trough, but by a deep tectonic fault. Moreover, the straits are of an oceanic nature. The flora and fauna of the islands of the continental slope is very different from the mainland and is generally island in nature. Examples of continental slope islands are the following: Madagascar, Greenland, etc.
Orogenic islands represent a continuation of the mountain folds of the continents. So, for example, Sakhalin is one of the folds of the Far Eastern mountainous country, New Zealand is a continuation of the Urals, Tasmania is the Australian Alps, the islands of the Mediterranean Sea are branches of the Alpine folds. The New Zealand archipelago is also of orogenic origin.
Island arcs garlands border East Asia, America and Antarctica. The largest region of island arcs is located off the coast of East Asia: the Aleutian ridge, the Kuril ridge, the Japanese ridge, the Ryukyu ridge, the Philippine ridge, etc. The second region of island arcs is located off the coast of America: the Greater Antilles, the Lesser Antilles. The Tritium region is an island arc located between South America and Antarctica: the Tierra del Fuego archipelago, the Falkland Islands, etc. Tectonically, all island arcs are confined to modern geosynclines.
Mainland offshore islands have different origins and represent different types of coastline.
Independent islands have never been parts of continents and in most cases were formed independently of them. The largest group of independent islands are volcanic.
There are volcanic islands in all oceans, especially in areas of mid-ocean ridges. The size and features of volcanic islands are determined by the nature of the eruption. Fissure lava outpourings create large islands, not inferior in size to platform islands. The largest island of volcanic origin on Earth is Iceland (103 thousand km 2).
The main mass of volcanic islands is formed by eruptions of the central type. Naturally, these islands cannot be very large. Their area depends on the nature of the lava. The main lava spreads over long distances and forms shield volcanoes (for example, the Hawaiian Islands). An eruption of acidic lava forms a sharp cone of a small area.
Coral islands are the waste products of coral polyps, diatoms, foraminifera and other organisms. Coral polyps are quite demanding in terms of living conditions. They can live only in warm waters with a temperature not lower than 20 0 C, therefore coral structures are common only in tropical latitudes and extend beyond them only in one place - the Bermuda Islands, washed by the Gulf Stream.
Depending on their location in relation to modern land, coral islands are divided into the following three groups:
coastal reefs,
barrier reefs,
Coastal reefs they begin directly off the coast of the mainland or island at low tide and border it in the form of a wide terrace. Near river mouths and near mangroves, they are interrupted due to low salinity of the water.
