Earth is a cosmic body that is part of the solar system. Considering the origin of the continents and oceans, it is worth touching on the issue of the origin of the planet.
How our planet was formed
The origin of the continents and oceans is a second question. The first is to explain the causes and method of Earth formation. His decision was still dealt with by the pundits of antiquity. Many hypotheses have been put forward explaining the origin of the Earth. Their consideration is the prerogative of astronomy. One of the most common is the hypothesis of O.Yu. Schmidt, which claims that our planet arose from a cold cloud of gas and dust. The particles included in its composition, during rotation around the Sun, were in contact with each other. They stuck together, and the resulting lump increased in size, its density increased, the structure changed.
There are other hypotheses that explain the appearance of planets. Some of them suggest that cosmic bodies, including the Earth, are the result of explosions in outer space of high power, which resulted in the decay of stellar matter. Many scientists are still engaged in the search for truth in the question of the origin of the planet.
The structure of the earth's crust under the continents and oceans
Studying the origin of the continents and oceans 7th grade high school. Even students know that the upper layer of the lithosphere is called the earth's crust. It is like a “cape” covering the seething bowels of the planet. If you compare it with other layers of the Earth, then it will seem the thinnest film. Its average thickness is only 0.6% of the radius of the planet.
The origin of the continents and troughs of the oceans that determine the appearance of the Earth will become clearer if we first study the structure of the lithosphere. The earth's crust consists of continental and oceanic plates. The first consists of three layers (bottom-up): basalt, granite and sedimentary. Oceanic plates are deprived of the last two, so their thickness is significantly less.
Differences in plate structure
The question that geography studies (grade 7) is the origin of the continents and oceans, as well as the distinguishing features of their structure. According to the vast majority of scientists, only oceanic plates originally appeared on Earth. Under the influence of processes occurring in the earth's interior, the surface became folded, mountains appeared. The bark became thicker, ledges began to appear, which later turned into continents.
Further transformation of the continents and oceanic depressions is not so clear. The opinions of scientists on this issue were divided. According to one hypothesis, continents do not move, according to another - they constantly move.
Recently, another hypothesis of the structure of the earth's crust has been substantiated. The basis for it was the theory of the movement of continents, the author of which was A. Wegener at the beginning of the 20th century. He at one time was not able to answer the legitimate questions about the forces that make the continents drift.
Lithosphere plates
The upper layer of the mantle in conjunction with the earth's crust is the lithosphere. The origin of the continents and oceans is closely related to the theory of plates that are able to move, and not shackled monolithically. The earth's crust has many cracks reaching the mantle. They break the lithosphere into huge areas having a thickness of 60-100 km.
Joints of plates coincide with ocean ridges passing in the middle of the oceans. They look like huge ramparts. The border may be in the form of gorges passing along the ocean floor. Cracks exist on the territory of the continents, pass through mountain ranges (Himalayas, Urals, etc.). We can say that these are old scars on the body of the Earth. Relatively fresh faults also exist, including crevices in eastern Africa.
Found 7 huge blocks and dozens having small areas. The main number of plates is captured by oceans and continents.
The movement of plates of the lithosphere
Under the plates there is a fairly soft and plastic mantle, which makes their drift possible. The hypothesis of the origin of continents and oceans states that the blocks are set in motion due to forces arising from the movement of the substance in the upper part of the mantle.
Strong currents directed from the center of the Earth cause discontinuities in the lithosphere. This type of fault can be seen on the continents, but most of them are in the zone of mid-ocean ridges under the thickness of ocean waters. At this point, the crust of the earth is much thinner. Substances in the molten state rise from the depth of the mantle and, having pushed the plates, increase the thickness of the lithosphere. And the edges of the plates are moved in opposite directions.
Parts of the earth's crust move from the ridges at the bottom of the oceans to the gutters. The speed of their movement is 1-6 cm / year. These figures are obtained thanks to satellite images taken in different years. The contacting plates move towards, along or diverge. Their movement along the upper layer of the mantle resembles ice floes on water.
When two plates move towards each other (oceanic and continental), the first, after bending, goes under the second. The result is deep gutters, archipelagos, mountain ranges. Examples: Islands of Japan, Andes, Kuril Trench.
When mainland plates collide, folding occurs as a result of creasing of the edges containing sedimentary layers. So the Himalayan mountains appeared at the junction of the Indo-Australian and Eurasian plates.
Continent evolution
Why is geography studying the origin of continents and oceans? Because an understanding of these processes is necessary for the perception of other information related to this science. The theory of lithospheric plates suggests that only one mainland first appeared on the planet, the rest of the Earth’s surface was occupied by the oceans. The appearing deep fractures of the crust led to its division into two continents. Laurasia is located in the northern hemisphere, and Gondwana is located in the southern hemisphere.
All new cracks appeared in the earth's crust, they led to the division of these continents. There were continents that exist now, as well as oceans: Indian and Atlantic. The basis of modern continents are platforms - aligned, very ancient and stable areas of the crust. In other words, these are plates that were formed by geological standards for a long time.
In places where parts of the earth's crust collided, mountains turned out. On some continents, traces of the contact of several plates are visible. Their surface area gradually increased. In a similar way the Eurasian continent arose.
Plate motion forecast
The theory of lithospheric plates suggests calculations of their future movement. Calculations made by scientists indicate that:
- Indian and Atlantic oceans will increase.
- The African continent will be shifted towards the northern hemisphere.
- The Pacific Ocean will become smaller.
- The Australian mainland will overcome the equator and join the Eurasian.
According to forecasts, this will happen no earlier than in 50 million years. However, these results need to be clarified. The origin of the continents and oceans, as well as their movement, is a very slow process.
In the mid-ocean ridges, the formation of new lithospheric plates. The oceanic crust that has arisen smoothly diverges away from the fault. After 15 or 20 million years, these blocks will reach the mainland and go under it into the mantle, which created them. The cycle of lithospheric plates at this closes.
Seismic belts
Studies the origin of the continents and oceans of the 7th grade of a comprehensive school. Knowing the basics will help students understand more complex subjects. The joints between the plates of the lithosphere are called seismic belts. These places clearly demonstrate the processes occurring at the border of the plates. The vast majority of volcanic eruptions and earthquakes are confined to these areas. Now there are about 800 volcanoes on the planet.
The origin of the continents and oceans needs to be known for predicting natural disasters and finding minerals. There is an assumption that in the places of contact of the plates as a result of the ingress of magma into the crust, different ores are formed.