Geography. The origin of the continents and oceans
Our Earth was probably formed 4.5 billion years ago as a result of the Big Bang. Like other planets in our solar system. The history of its development still worries scientists. We get acquainted with the origin of the continents and oceans in the 7th grade. However, these generally accepted theories, alas, are not always true. In addition, the geophysicists themselves doubt them. Because research history of our planet continues today.
So, our Earth was formed from a protoplanetary disk, dust and gases. Initially, its surface was heated due to frequent collisions with other space bodies.
But soon the bombing stopped. This gave the planet the opportunity to form a hard crust. Subsequently, water appeared on Earth (the theory of its origin will be discussed below).
Was or was not
At the beginning of the 20th century, scientists believed that our Earth did not undergo significant changes throughout its existence.The continents have not changed for billions of years. However, soon another hypothesis was proposed for the origin of continents and oceans.
Alfred Wegener noticed that the continents have similar outlines along the coastline. This suggests that once they were one. A German geophysicist in his research claimed that 250 million years ago all the continents were part of the same supercontinent. And the first supercontinent Wegener considered Pangea. But today there are suggestions that before it there were other super continents.
There is a theory that initially only one continent existed on Earth - Rodinia, which washed the ocean of Mirovia. In class 7 geography, the origin of the continents and oceans is not mentioned in Rodinia. This is because it is a hypothetical supercontinent whose existence cannot be confirmed or refuted.
Both names are taken from the Russian language (race and world). Rodinia is the oldest supercontinent known to us today. Recently on the island of Mauritius, in the Indian Ocean, zircon was discovered in the sand. It is believed that this may indirectly confirm the existence of Rodinia.
However, its position and form still cause controversy among scientists. Geophysicists believe that other supercontinents could exist before it. Later Rodinia fell to continents. Then they merged again. And they broke up again. These processes took millions of years, but they were repeated with surprising regularity. It is assumed that in the future all of our continents will come together again. It will happen in 200-250 million years. Alas, this information is not found on the origin of the continents and oceans in the 7th grade. The GEF, however, requires students to know this theory.
Super Continent Pangea
After this, the mainland Pangea was formed (from Lat.all earth). That's what Alfred Wegener called her. Pangea was washed by the ocean Tethys. Today, Tethys particles are deep-water parts of the Mediterranean, Caspian and Black Seas.
Laurasia and Gondwana
Pangea split into 2 parts - Laurasia and Gondwana. Parts of Gondwana became the basis of the continents, which gradually moved away from each other. In the end, each of them took the current position. Thus she became the mother of the following continents - Africa, Australia, Antarctica, South America.
Laurasia divided into North American and Eurasian plate. By the way, Eurasia is a unique continent, which was formed from three lithospheric plates - Eurasian (part of Laurasia), Arabian and Indostan (parts of Gondwana). The lithospheric plates, coming closer together, literally destroyed the ocean of Tethys. The rapprochement was also accompanied by the formation of mountains - the Caucasus and the Armenian Highlands.
Only about 65,000 years ago, the continents occupied their present position.
Today, satellites record the movement of lithospheric plates, which is imperceptible to the human eye. Just a few centimeters per year. However, over the course of millions of years, these plates have changed their location beyond recognition. Scientists believe that the cause of the plate movements is the circulation of the mantle inside the Earth. And this movement will continue until it is completely cooled.
This is what the future Super Continent Pangea Ultima will look like.
Origin of the continents
According to geophysicists, those materials that were originally in the depths of the Earth, but soon came to the surface, are part of the Earth’s crust. The fact is that the heaviest metals descend into our core, while the lighter ones rise to the surface. The composition of the earth's crust is dominated by silicon, oxygen, aluminum, iron.
With varying intensity over billions of years, the formation of the lithosphere occurred. Every student knows about the origin of the continents and oceans in Grade 7, but the details of this formation are not known to everyone. Scientists say that these processes occur continuously. At the same time, epochs of magmatic and tectonic activity were replaced by periods of rest
Scientists believe that active volcanism occurred 3.5 billion years ago. He was accompanied by a volumetric emission of gases. Thus began the era of the Archean. Lithospheric plates, which today became the cores of our continents, gradually increased their mass. On the outskirts of ancient platforms, active mountain-building processes took place as a result of their collisions. Thus arose the most massive mountain systems - the Ural Mountains, Tibet, Karakorum and others. In the same period young plates were formed - Scythian, Western, Turan.
Where on earth water
Finding out the origin of the continents and oceans, scientists have been asking themselves for decades where the water came from on Earth. This is the most mysterious and unexplored substance. At first glance, it seems to be a simple combination of hydrogen and oxygen, but it is not.It is an indicator of heat and cold.
Almost of the surface of the planet is occupied by seas, oceans, rivers and lakes. 20% of the land is covered with ice. And our climate depends on water. For example, the course of the Gulf Stream forms the weather in Norway and even in the north of the Crimea.
Our planet would have long ago become a piece of solid, lifeless stone, if not for water resources.
The following version is generally accepted in Class 7 geography on the origin of continents and oceans. Oxygen and hydrogen are very common substances in space. Scientists were convinced that water came to Earth thanks to cosmic bodies, which were especially actively bombarding the planet in the first billion years of its life. Probably, when the planet was still in the embryo stage, celestial bodies fell on it, which were formed at the far boundaries of the planet. A large amount of ice could be present in the composition of comets and asteroids.
For example, white dwarfs (large stars) tend to absorb matter and distribute it over their surface. One such star can provide water for a third of our oceans.
However, recent studies have disproved the theory of the extraterrestrial origin of water on Earth. Geophysicists conducted an experiment, the results of which became known in January 2017.Most likely, the water on the planet appeared due to chemical reactions occurring in its depths.
For the experiment, the conditions typical for the depths of our planet were simulated on a computer - temperatures up to 1,400 ° C and pressures 20 times higher than atmospheric.
In such conditions, silicon dioxide, which is part of the mantle, reacts with hydrogen. This leads to the formation of liquid water. At the same time during its release to the surface of the Earth can shake from powerful earthquakes.
Today, scientists are trying to find out if this experiment explains the appearance of the oceans on the planet. Or is there still a theory about the extraterrestrial origin of water.
Names of continents and oceans
So, let's discuss the origin of the names of the continents and oceans. Where did they come from and what do they mean?
Modern names were given to continents and oceans not so long ago. Since the scholars of antiquity did not have enough information, the names given by them were not correct. For example, the Atlantic Ocean, many Greek scientists in their treatises called the Western, and the Arab geographers and the Sea of Darkness. The Pacific Ocean was originally the South Sea.But later Magellan, who had not met a single storm during the voyage, called him Silent. In fact, it is the Pacific Ocean that is the most hectic
The modern names of the continents and oceans were mostly given by the navigators who discovered them. So, Australia (australius - south) Flinders dubbed it so because it is located in the southern hemisphere.
Africa got its name from the Afri tribes that its discoverers faced. America is named after Amerigo Vespucci, whose expedition was the first to reach the New World.