The Earth is a cosmic body that is part of the solar system. Considering the origin of continents and oceans, it is worth touching on the question of the emergence of the planet.
How our planet was formed
Происхождение материков и океанов – вопрос второй.The first is to explain the causes and way of the formation of the Earth. His decision was still engaged in scholars 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 has arisen from a cold cloud of gas and dust. Particles in its composition, during rotation around the sun 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 explaining the appearanceplanets Some of them suggest that cosmic bodies, including the Earth, are the result of explosions in high-power space, to which the decay of stellar matter led. The search for the truth in the question of the origin of the planet is still engaged in many scientists.
The structure of the earth's crust under the continents and oceans
Studies the origin of continents and oceans Grade 7high school. Even students know that the upper layer of the lithosphere is called the crust. It is similar to the “cape” that covers the raging bowels of the planet. If you compare it with other layers of the Earth, it will seem like the thinnest film. Its average thickness is only 0.6% of the radius of the planet.
The origin of the continents and depressions of the oceans,determine the appearance of the Earth, it will become clearer if you first study the structure of the lithosphere. The crust consists of continental and oceanic plates. The first consists of three layers (bottom-up): basalt, granite and sedimentary. Oceanic plates are devoid of the last two, so their thickness is substantially less.
Differences in plate structure
Question that studies geography (Grade 7) -the origin of the continents and oceans, as well as the distinctive features of their structure. According to the overwhelming 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.
The further transformation of the continents and oceanicdepressions are not so straightforward. The opinions of scientists on this issue are divided. According to one hypothesis, the continents do not move, on the other - they are constantly moving.
Recently another hypothesis was substantiated.structure of the earth's crust. It was based on the theory of the movement of continents, the author of which was A. Wegener at the beginning of the 20th century. He was not able to answer the legitimate questions about the forces that make the continents drift.
Lithospheric plates
The upper layer of the mantle in conjunction with the crust- this is the lithosphere. The origin of the continents and oceans is closely related to the theory of plates, which are capable of moving, and not monolithic constrained. The crust has many cracks reaching the mantle. They break the lithosphere into huge areas, having a thickness of 60-100 km.
The joints of the plates coincide with the oceanic ridges,passing in the middle of the oceans. They look like huge shafts. The border may be in the form of gorges, passing along the bottom of the ocean. Cracks exist on the territory of the continents, pass through the mountain ranges (Himalayas, Urals, etc.). We can say that these are old scars on the body of the Earth. There are relatively fresh rifts, these include crevices in eastern Africa.
Found 7 huge blocks and dozens with small areas. Most of the plates capture the oceans and continents.
Plate movement of the lithosphere
Under the slabs is quite soft andplastic mantle that makes them drift possible. The hypothesis of the origin of continents and oceans says that the blocks are driven by the 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 breaks in the lithosphere. You can see this type of faults on the continents, but most of them are located in the zone of the mid-ocean ridges under the ocean waters. In this place the bark of the earth is much thinner. Substances in the molten state rise from the depth of the mantle and, pushing the plates, increase the thickness of the lithosphere. And the edges of the plates move in opposite directions.
Parts of the crust move from the ridges at the bottomoceans to the gutters. The speed of their movement is 1-6 cm / year. These figures were obtained thanks to satellite images taken in different years. The adjoining plates move towards, along or diverge. Their movement on the upper layer of the mantle resembles ice floes on the water.
When two plates move towards each other(oceanic and mainland), then the first, making a bend, goes under the second. The result is deep troughs, archipelagoes, mountain ranges. Examples: islands of Japan, Andes, Kuril Trench.
In the collision of continental plates, folding is formed as a result of creasing edges containing sedimentary layers. Thus, the Himalayan mountains appeared at the junction of the Indo-Australian and Eurasian plates.
Continent evolution
Why is the geography the origin of the continents andoceans exploring? Because the understanding of these processes is necessary for the perception of the rest of the information relating to this science. The theory of lithospheric plates suggests that a single continent first appeared on the planet, the rest of the Earth’s surface was occupied by the World Ocean. The emerged deep faults 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.
Все новые трещины появлялись в земной коре, они led to the division of these continents. There are continents that exist now, as well as the oceans: Indian and Atlantic. The basis of modern continents are the platforms - leveled, very ancient and stable areas of the crust. In other words, these are plates that were formed by geological standards for a long time.
В местах, где участки земной коры сталкивались, turned out the mountains. Traces of contact of several plates are visible on separate continents. The area of their surface gradually increased. Similarly, the Eurasian continent arose.
Plate motion forecast
The theory of lithospheric plates suggests calculations of their future movement. Calculations that were made by scientists say that:
- Indian and Atlantic oceans will increase.
- The African continent will be shifted towards the northern hemisphere.
- The Pacific Ocean will be smaller.
- The Australian mainland will overcome the equator and join the Eurasian.
According to forecasts, this will happen no sooner 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 occursthe formation of new lithospheric plates. The oceanic type crust that arises gradually diverges to the sides of the fracture. After 15 or 20 million years, these blocks will reach the mainland and go under it to the mantle, which created them. The circulation of lithospheric plates on this closes.
Seismic belts
Studies the origin of continents and oceans Grade 7secondary school. Knowledge of the basics will help students understand more complex issues in the subject. The junctions between the plates of the lithosphere were called seismic belts. These places clearly demonstrate the processes occurring at the plate boundary. The vast majority of volcanic eruptions, earthquakes are confined to these areas. Now there are about 800 volcanoes on the planet.
The origin of the continents and oceans is necessaryknow to predict natural disasters and search for 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.
