The most important morphological feature of the modern surface of the Earth is the uneven distribution of land and sea on the earth's surface with a decisive predominance of water space.
The ratio of land and water areas on the earth's surface is 1: 2.43. V.I. Vernadsky believed that in the geological past this ratio could vary from 1.93 to 7.79. From the indicated change in the ratio of land and sea, it is assumed that during geological time the volume of waters of the World Ocean remained unchanged. At present this assumption is implausible. Changes in the geological past of the volume of water in the hydrosphere, along with geotectonic development, determined the constant change in the relationship between land and sea.
According to N.M. Strakhov, as we moved further into the geological past, the area of the seas on the platforms decreased due to the increasing distribution of deep geosynclinal seas. Regarding the early stages of geological history, it is known that shallow seas predominated in Precambrian and Lower Paleozoic times. A. B. Ronov provides data on the areas occupied by geosynclinal and platform seas from the Lower Devonian to the Lower Jurassic. The data obtained by Ronov are in good agreement with information about changes in the relationship between land and sea in the geological past, obtained by another method. Comparison of them shows that in the Triassic the land occupied the largest surface area, but later it began to give way to an expanding area of marine spaces. The predominance of sea basin areas, which increased sharply starting from the Jurassic period, can be related to the expansion and deepening of the oceans that began at that time. We can talk about a directional change in the ratio of land and sea area on the earth's surface, which was determined by the tectonic development of the earth.
The idea of the heterogeneous distribution of land and water over the earth's surface, of its division into continental and water hemispheres, developed back in the 18th century. On the continental hemisphere c. Currently, land occupies 39.3% of its surface, and water 60.7%; in the oceanic hemisphere, water accounts for 80.9% and land for 19.1%. The relationship between the average depths of the oceans in these hemispheres is interesting. In the continental hemisphere, the average depth is 3320 m, in the oceanic hemisphere 4070 m. Comparing the average height of land with the average depth of the ocean for the continental and oceanic hemispheres, we find that it is significantly different, the difference in the average height of the continents for both hemispheres is 450 m. Even greater the difference between the average height of the land and the average depth of the oceans. This value gives an idea of the amplitude of the dismemberment of the earth's surface. For the continental hemisphere, this difference is 570 m, and for the oceanic hemisphere 3270 m. Note that, according to Cossipa, the average level of the earth's crust in the continental hemisphere is 1420 m, and in the oceanic hemisphere 2346 m. Consequently, the masses of the earth's crust in the continental hemisphere are raised, and in the oceanic lowered relative to the average level (2440 m) of the earth's crust.
It is remarkable that the indicated difference for the continental and oceanic hemispheres is equivalent and amounts to 1020 m. Consequently, the distribution of masses of the earth's crust and the associated distribution of land and water in the continental and oceanic hemispheres do not represent a surface phenomenon on the Earth, but reflect the state of isostatic equilibrium between the masses of the earth bark. This is clearly confirmed by V.I. Vernadsky, who drew attention to the fact that the current ratio of land and water areas on Earth (2.4-2.5) corresponds to the ratio of the specific gravities of continents and oceans (taken to the average depth of the World Ocean). This circumstance emphasizes the isostatic equilibrium in the distribution of continental and oceanic areas on the earth's surface. In the state of modern isostatic equilibrium of continental masses and oceans, researchers saw an expression of the fundamental difference in their geological nature. They believed that the continents were lighter, formed from sialic material, in comparison with the bottom of the oceans, which was composed of denser simatic masses.
It is assumed that such a difference in the structure of continents and the bottom of the oceans is due to the antiquity of the oceans and the existing isostatic equilibrium is a state that has long been established. This opinion is contradicted by the ratio of land and sea that has repeatedly changed in the geological past. It was determined by the tectonic development of the Earth and was accompanied by a significant movement of masses of the earth's crust. Under these conditions, it seems completely impossible for the isostatic equilibrium of the continents and oceans to remain unchanged. There is no doubt that in the course of geological time this balance was disturbed and its current state was determined by the youngest - neotectonic and modern tectonic movements. This means that the relationship between land and oceans, corresponding to a certain stage of development of structure and relief, is not a long-lasting phenomenon.
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Water is a resource, water is an energy carrier, water is a transport system, water is the basis of life. Therefore, water reserves have been calculated for a long time. Methods have been developed to determine the area and depth of water bodies, and instruments have been created to measure flow speed and other physical and chemical characteristics. All this allows us to estimate the water reserves on our planet.
It is believed that 70.8% of the earth's surface is covered with water. Therefore, our Earth can be called the Planet of Water, or the Planet of the Ocean. Indeed, the ocean occupies 360 million km2 with the total size of the planet's surface being 510 million km2. But in reality the hydrosphere is much larger. Thus, glaciers cover 16.3 million km2, or 11% of the land. Lakes and watercourses on land occupy a significantly smaller area - 2.3 million km2, or 1.7% of the land, swamps and wetlands - 3 million km2, or 2% of the land. Therefore, on Earth, not 360, but 380 million km2 of the surface, or 75%, are constantly covered with water. So, it is more correct to assume that 3/4 of the globe is constantly covered with water. However, we must not forget about winter. The largest area on land in winter is occupied by snow cover in the Northern Hemisphere - 59 million km2. During this period of the year, the area occupied is 439 million km2, or 86% of the entire surface of the globe. Snow covers paths, roads, sidewalks, and people are forced to put up with the whims and whims of nature.
In order to accurately determine the areas covered by water on Earth, it was necessary to construct accurate maps of the entire planet, especially the ocean. Back in the 18th and early 19th centuries. no such maps existed. Therefore, many scientists believed that the ocean occupies only half of the surface of the globe. Only in the 20th century. learned to determine the area of water bodies. But to estimate water volumes, you need to have a depth map, and to determine river flow, you need to be able to measure water flow rates. Even during the first flights into space, science knew more about it than about the bottom topography and the depths of the ocean. And only in the second half of the 20th century. scientists were able to answer many questions that arose before us when studying. If the ocean is a single mass of water, then on land the hydrosphere consists of many separate water bodies, both on the surface and underground. There are tens of millions of them. Therefore, observations and measurements are carried out only for fairly large objects; as a result, the accuracy of data on the volumes of water bodies on land is lower than for the ocean. Over the entire existence of the Earth, according to the estimates of the Russian scientist O. G. Sorokhtin, 2.17 billion km3 of water were degassed from its depths. But not all of this water entered the hydrosphere. Part of it went to form the earth's crust. And the remaining water formed the planet’s hydrosphere with a volume of 1.5 billion km3. The bulk of the water is in. It contains 1370 million km3 of water. But this water is of little use for farming, since each liter contains an average of 35 g of salts. Glaciers contain 28 million m3 of water (the volume of ice is converted into the volume of water, since ice is lighter than liquid water). About 100 million km3, but this is not an exact figure, since it is impossible to take into account all groundwater. The remaining water bodies can be called small compared to the ocean. Among them, the largest are lakes. The total volume of water in lakes is estimated differently, depending on whether the Aral Sea is also classified as lakes. The difficulty of estimation also lies in the huge number of lakes on Earth, the total volume of water of which has never been measured. The soil contains about 10 thousand km3 of water, and swamps contain about the same amount. At any given moment, river beds contain only 2 thousand km3 of water, and
What is land? This is that part of the earth's surface that is not hidden by water bodies, from the world's oceans to lakes, rivers and reservoirs. Thus, land can be understood as any part of a continent or island that is not flooded with water.
What is the percentage of land on our planet? A little less than a third of it is given to forests (approximately 27%), even less (21%) - to natural pastures, a little less than 10% is occupied by arable land and the same amount - by irrationally used land.
Another 11% each falls on deserts and glaciers. Most of the latter lies, as you might guess, in Antarctica. Cities occupy in total no more than 1% of the entire landmass of the Earth.
How much land area on Earth is according to scientists? The vast majority of the surface of our home planet is devoted to a body of water called the world ocean. And only 29% of it is occupied by continents, which in numerical terms equals approximately 149 million square kilometers. They are based on the earth's crust, its thickness varies in different places from 25 kilometers or more. Modern geography recognizes continents as 6 main and largest areas into which the landmass of planet Earth is divided: Africa, Eurasia, South and North America, as well as relatively small Australia and Antarctica.
The championship in size, as is known from a school geography course, belongs to Eurasia, stretching with its intricately broken coastline from Cape Roca in the west to Cape Dezhnev in the east for the entire 16,000 kilometers. Its territory is more than 50 million square meters. km. And this is the only continent, standing on the coast of which, you can admire the view of one of any four world oceans.
Africa confidently holds second place in the ranking of “The largest landmass on the planet”. Its midline (about half the distance between the extreme northern and southern points) is located almost exactly on the equator. From the north, the mainland is connected to the aforementioned champion Eurasia only by the narrow Isthmus of Suez.
North America is in third place. It lies entirely in the northern hemisphere and occupies just over 24 million square meters. km from the territory that represents the entire landmass of the planet. Three oceans (Atlantic, Pacific and Arctic) wash its shores. The Bering Strait, which serves as a natural border between it and Eurasia, as scientists think, did not exist in ancient times: in its place there was an isthmus that connected the continents.
The other America (South) is located mainly in tropical and equatorial latitudes. Its coastline is less indented, and the area of the mainland washed by the Atlantic and Pacific oceans (and from the north - the Caribbean Sea), together with all the islands, is about 17.8 million square meters. kilometers. It is the fourth largest landmass on the planet.
Who is the outsider in this ranking? The smallest of the continents is Australia (only 7.6 million square kilometers). Its territory is located completely below the equator line. There are no land connections between this small green continent and the rest, from which Australia is significantly removed.
Antarctica stands somewhat apart from its fellow continents. This is the most sparsely populated of all the parts into which the planet's land is divided. And it is not surprising, because its entire territory (which is about 14 million square kilometers) lies completely below the Antarctic Circle, and the geographical center of the continent practically falls on the South Pole. The entire area of the continent is completely hidden under an impenetrable layer of ice and snow.
What do we know about the oceans? Of the 4 water giants that our planet has, the leadership in size and depth, of course, belongs to the Quiet. Its total volume is over 1300 million cubic kilometers, and its area with all the seas is more than 170 million square kilometers. km. If its average depth is approximately 4000 meters, then the maximum is more than 11000 meters. On its territory there is also the largest concentration of islands.
The smallest of the oceans is the Arctic Ocean; only 4% of the Earth's water surface is allocated for it. It is 3 times smaller than the other three giant oceans. Moreover, it is the most difficult to reach. This is due to a multi-year ice layer more than 4 meters thick. A path called the Northern Sea Route has been laid through it; along it you can get from the European part of our native country to the Far East.
Since school, each of us knows in every detail the outlines of the continents and the largest islands. But they weren't always like this. Scientists have long proven that the Earth's lithosphere is made up of tectonic plates, whose destiny is to move through the mantle lying underneath them.
The age of our globe, according to scientists, is approximately four and a half billion years. Already in the Archean era (the oldest in earthly history), the Earth consisted of oceans and continents, the outlines of which, however, were far from modern ones. Both then and today, the continental crust was and is being formed from rocks melted in the depths of the earth’s interior and brought to the surface.
The entire lithosphere is represented by tectonic plates that can approach, diverge, and collide with each other. During these collisions, any of them can go deeper, plunging under the neighboring one. In areas of such dives, active volcanoes and deep ditches are formed.
Where plates diverge, deep cracks cross the earth's crust. The rocks melt to form basalt, which rises up, filling these cracks, and hardens in the upper layers of the Earth's crust. In place of the ocean, when plates diverge, an ocean floor with underwater ridges is formed.
In the past, most of the modern southern continents existed together in the form of a giant continent, called Gondwana by scientists. The joining of ancient continents occurred during the Paleozoic era, which began at a time mark about half a billion years ago from the present, and lasted for about 300 million years.
At the end of this period, the movement of tectonic plates led to the connection of Gondwana with other continents. The result was a huge landmass that united almost all the ancient continents.
Scientists geologists gave this single continent a name - it was Pangea, it was located from the North to the South Pole. The mountain systems that currently exist in North America, Asia, and Australia are the result of the convergence of tectonic plates.
The division of the single continent of Pangea into separate continents began hundreds of millions of years later. As a result, the planet's land (continents) and oceans in their outlines gradually approached those that we are accustomed to seeing on modern geographical maps.
For many years, geologists doubted the plausibility of the theory of continental drift, that is, the ability of continents to move closer and further away. But scientific data collected in the sixties of the last century dispelled these doubts.
The outer shell of the earth (lithosphere), being solid and extending deep into the globe up to one hundred kilometers, consists of tectonic plates. These plates can move because deep in the lithosphere, the Earth's mantle is a much more liquid, high-temperature substance that supplies energy for the movement of tectonic plates.
Now the number of large and medium-sized lithospheric plates is about 10. These include the Eurasian, African, Pacific and others. They move at a speed of several centimeters annually. This is how the process of separation of America, Europe and Africa began about 180 million years ago. At the same time, an ocean formed between them, now called the Atlantic.
Looking at a modern world map, you can see that the coastal contours of the continents separated by the Atlantic Ocean coincide quite accurately. Of course, such a coincidence is not the only argument in favor of the theory of continental divergence. Scientists have collected evidence using the latest scientific research in the fields of geology and oceanography.
Water - a necessary substance that is needed for the basis of life. Scientists believe that water appeared on Earth after the formation of the planet. Some theories say that this liquid came to us thanks to meteorites that were covered with ice.
It is believed that water occupies 70.8% of the Earth's surface. For this reason, our Earth is called the “Planet of Water” or “Planet of the Ocean”. The total size of the planet's surface is 510 million km2, and the ocean occupies 360 million km2. Also, do not forget about the glaciers, which cover 16.3 million km2. Swamps, land, lakes, watercourses and other wetlands now occupy about 5 million km2. Therefore, we can say that about 75% of the surface of the globe is covered with water (3/4 of the Earth is occupied by water).
Also be aware of winter snow cover. The snow cover of the Northern Hemisphere covers the largest area in winter - 59 million km2. During this period of the year, the area occupied by the hydrosphere is about 440 million km2, or more than 85% of the surface of our planet. In winter, snow falls and covers vast areas - roads, highways, streets, paths, sidewalks.
In 2002, Japanese scientists conducted an experiment in which they suggested that under the Earth, in its lower mantle, there is 5 times more water than on the surface.
Seas, oceans, rivers and lakes make up more than 70% of the Earth's area, the rest is land. The deepest ocean on the planet is the Pacific. The maximum depth of this giant is 11.8 km. On average, the depth of the oceans is 3800 meters.
All living things on the planet need water. Fresh water makes up only 3% of all water reserves on Earth, and 97% is salty. Today the largest fresh lakes are Onega, Baikal, Ladonezh, and Caspian. Also, precipitation is the main supplier of fresh water for the Earth.
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