Origin of continents and oceans (Grade 7). Origin of continents and oceans: hypothesis, description and history

The earth is a cosmic body that is part of the solar system. Considering the origin of continents and oceans, it is worth mentioning the origin of the planet.

How our planet was formed

The origin of continents and oceans is a matter of the second. The first is to explain the causes and way of the formation of the Earth. His decision was also occupied by the learned men of antiquity. Many hypotheses have been advanced 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, in which it is asserted that our planet originated from a cold cloud of gas and dust. The particles in its composition, during rotation around the sun, were in contact with each other. They coalesced, and the resulting clump increased in size, its density increased, the structure changed.

There are other hypotheses explaining the appearance of planets. Some of them suggest that the cosmic bodies, including the Earth, are the result of explosions in outer space of high power, to which led the decay of stellar matter. Many scientists are still searching for the truth about the origin of the planet.

The structure of the earth's crust under the continents and oceans

Studying the origin of the continents and the oceans of the 7th grade of secondary school. Even students know that the upper layer of the lithosphere is called the earth's crust. It is like a "cape" covering the turbulent depths 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 depressions of the oceans, which 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 consist of three layers (bottom-up): basaltic, granite and sedimentary. The oceanic plates are devoid of the last two, so their thickness is much smaller.

Differences in the structure of plates

The question that geography studies (Grade 7) is the origin of continents and oceans, as well as the distinctive features of their structure. According to the overwhelming majority of scientists, on the Earth initially there were only oceanic plates. Under the influence of processes occurring in the earth's interior, the surface became folded, mountains appeared. The bark became thicker, and protrusions began to appear, which later became continents.

The further transformation of continents and oceanic depressions is not so unambiguous. The opinions of scientists on this issue were divided. According to one hypothesis, the continents do not move, on the other - they constantly move.

Recently, another hypothesis of the structure of the earth's crust was justified. The basis for it was the theory of the displacement of continents, the author of which was A. Wegener at the beginning of the 20th century. At one time, he was unable to answer legitimate questions about the forces that make the continents drift.

Lithospheric plates

The upper layer of the mantle, together with the earth's crust, is the lithosphere. The origin of continents and oceans is closely connected with the theory of plates, which are able to move, and not constrained 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.

The joints of the plates coincide with the oceanic ridges passing in the middle of the oceans. They look like huge trees. The border can be in the form of gorges, passing along the bottom of the ocean. Cracks exist on the territory of the continents, they pass along mountain ranges (the Himalayas, the Urals, etc.). It can be said that these are old scars on the body of the Earth. There are also relatively fresh faults, these include clefts in the east of Africa.

Found 7 huge blocks and dozens of small areas. The main number of plates is captured by the oceans and continents.

Movement of plates of the lithosphere

Under the plates is a soft enough and plastic mantle, which makes possible their drift. The hypothesis of the origin of continents and oceans says that the blocks are set in motion by 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 fault on the continents, but most of them are in the zone of mid-ocean ridges under the oceanic water column. At this point the earth's crust is much thinner. Substances in the molten state rise from the depth of the mantle and, having shoveled 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 ridges on the ocean floor to the gutters. The speed of their movement is 1-6 cm / year. The figures are obtained due to satellite images taken in different years. The adjoining plates move towards, along or diverge. Their movement along the upper layer of the mantle resembles ice floes on the water.

When two plates move towards each other (oceanic and continental), the first one, making a bend, leaves under the second one. The result is deep gutters, archipelagos, mountain massifs. Examples: the islands of Japan, the Andes, the Kuril Trench.

When the continental plates collide, folding is formed as a result of crushing of the edges containing sedimentary layers. So the Himalayan mountains appeared at the junction of the Indo-Australian and Eurasian plates.

Evolution of continents

Why is the geography of the origin of the continents and the oceans studying? Because understanding these processes is necessary for the perception of the rest of the information related to this science. The theory of lithospheric plates says that on the planet first there was only one continent, the rest of the Earth's surface was occupied by the World Ocean. The deep crustal debris that has appeared has led to its division into two continents. In the northern hemisphere, Laurasia is located, and in the southern hemisphere - Gondwana.

All the new cracks appeared in the earth's crust, they led to the division of these continents. There are continents existing now, as well as the oceans: the Indian and the Atlantic. The basis of modern continents are platforms - aligned, very ancient and stable areas of the crust. In other words, these are slabs that have been formed by geological standards for a long time.

In places where parts of the earth's crust collided, the mountains turned out. On separate continents, traces of contact of several plates are visible. The area of their surface gradually increased. Similarly, the Eurasian continent emerged.

Forecast of plate movement

The theory of lithospheric plates assumes calculations of their future displacement. The calculations, which were made by scientists, say that:

• The Indian and Atlantic oceans will increase.
• The African continent will be displaced towards the northern hemisphere.
• The Pacific Ocean will be less.
• The Australian mainland will cross the equator and join the Eurasian one.

According to forecasts, this will not happen before 50 million years. However, these results need to be clarified. The origin of continents and oceans, as well as their movement, is a very slow process.

In the mid-oceanic ridges, new lithospheric plates are formed. The crust of the oceanic type that emerges smoothly diverges from the fault. After 15 or 20 million years, these blocks will reach the mainland and go under it into the mantle that created them. The cycle of lithospheric plates closes on this.

Seismic belts

Studying the origin of the continents and the oceans of the 7th grade of the general education school. Knowing the basics will help students understand the more complex issues in the subject. The joints between the plates of the lithosphere have received the name of 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 continents and oceans must be known for predicting natural disasters and searching for minerals. There is an assumption that in the places of plate contact, as a result of magma entering the crust, different ores are formed.